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By pintoplumber - 12 Years Ago
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I wanted to keep this a secret, but I must let the cat out of the bag. I rebuilt the 239 this summer. Put in a 312 crank, 272 standard pistons with the skirts cut, and G heads. I kept the same cam and lifters in, Isky E4.
My problem is I'm only good up to about 2500 rpm's under load then it stumbles, misses, looses power. I pulled the timing cover off this weekend, and my machinist came over to check if I have the cam timed right.
I'm in the 2 degree retarded slot which if I did it right, gives me 3 degrees advance. Do I need to go back to the stock cam position or must I fatten up the jets? Does the G heads flow that much more that I'm running lean? It seems to me that when the outer 2 carbs come in that's when it stumbles.
I forgot to mention I have an edelbrock 354 3x2 intake.
Any thoughts appreciated.
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By The Master Cylinder - 12 Years Ago
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Dennis that should make for an interesting engine (sleeper?).
The first thought I have (and I am probably way off base) is does the 354 manifold seal OK around the ports on the "G" heads? I know that the later 573 manifold does not seal correctly to the earlier heads. Manifold leak would cause a lean mixture.
Also on my 3X2 I had a bad accelerator pump in on of the secondaries (I'm running 97's) that caused a BIG bog and was a beeauch to find when they opened. Don't know what carbies you have but you might check your pumps and power valves.
Another Dennis
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By NoShortcuts - 12 Years Ago
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Is this the first you've used the 3x2 set-up, Dennis, or had you used it prior to the rebuild?
The way it's dying on you, I'm wondering about the ignition system. Same ignition coil as before the rebuild?
And then there's the fuel pump diaphragm. The ethanol can cause problems with these...
The above said, you're indicating that you're suspicious that the problem is occurring as the front and rear carbs are beginning to open...
With the 272 bore and the 312 crank, it sounds like you've got 283 cubic inches. Interesting combination...
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By pintoplumber - 12 Years Ago
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The Master Cylinder (8/11/2013)
Dennis that should make for an interesting engine (sleeper?).
The first thought I have (and I am probably way off base) is does the 354 manifold seal OK around the ports on the "G" heads? I know that the later 573 manifold does not seal correctly to the earlier heads. Manifold leak would cause a lean mixture.
Also on my 3X2 I had a bad accelerator pump in on of the secondaries (I'm running 97's) that caused a BIG bog and was a beeauch when the opened. Don't know what carbies you have but you might check your pumps and power valves.
Another Dennis
I've got the mismatch sealed good. Sprayed starting fluid around the intake base, no increase in rpm's
I've got the ford/holly 94's power valve plugs in the end carbs. I've been running the 3x2's for 10 years now. The engine was running great prior to the rebuild.
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By pintoplumber - 12 Years Ago
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NoShortcuts (8/11/2013)
Is this the first you've used the 3x2 set-up, Dennis, or had you used it prior to the rebuild?
The way it's dying on you, I'm wondering about the ignition system. Same ignition coil as before the rebuild?
And then there's the fuel pump diaphragm. The ethanol can cause problems with these...
The above said, you're indicating that you're suspicious that the problem is occurring as the front and rear carbs are beginning to open...
With the 272 bore and the 312 crank, it sounds like you've got 283 cubic inches. Interesting combination...
I've been running the set up for 10 years, that's why it's such a puzzle. I've increased the stroke and have bigger heads.
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By Hoosier Hurricane - 12 Years Ago
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Dennis:
Maybe you should disconnect the linkage to the end carbs and see if it still sputters and misses above 2500. That would help steer you in the right direction. I wonder if the 354 manifold will flow enough air to satisfy your new engine, but it should not cause it to miss and stumble. It would just get lazy at high rpm from lack of air flow.
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By The Horvaths - 12 Years Ago
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Try running disconnecting secondaries. That may help to clear up any major timing/ignition issues. Then, if that goes well, try running only one secondary at a time?
Edit - Did you actually check cam timing or just verify which slot the key is in? If it doesn't behave on the primary carb alone, verify the timing curve. If that's reasonable, you might want to actually measure cam timing.
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By 312T85Bird - 12 Years Ago
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Ethanol???? Every one should be writing and calling there Congressman and senators and getting a stop put to Ethanol period !!!!! Why should we suffer so the Farm Lobbists and corn Farmers should prosper?? We have enough challenges keeping our old Horses on the road with out paying for fuel that hurts them.
312T85Bird
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By NoShortcuts - 12 Years Ago
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I agree with you. My understanding is that the use of the ethanol may be extending petroleum product, but the burning of the ethanol is actually producing more environmental pollution. I've also heard from others that some European countries are actually moving AWAY from ethanol use because of pollution issues they've measured.
I've heard that the EPA proposed move to a 15% ethanol mixture here in the U.S. may be catastrophic for some existing internal combustion engines. Everyone I've talked to who is dealing with small gas engines is negative about the use of ethanol in what they're working on or with.
Unfortunately, I have no sources to sight for the above second or third hand information. 
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By Dobie Gillis - 12 Years Ago
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NoShortcuts (8/12/2013)
I agree with you. My understanding is that the use of the ethanol may be extending petroleum product, but the burning of the ethanol is actually producing more environmental pollution. I've also heard from others that some European countries are actually moving AWAY from ethanol use because of pollution issues they've measured. I've heard that the EPA proposed move to a 15% ethanol mixture here in the U.S. may be catastrophic for some existing internal combustion engines. Everyone I've talked to who is dealing with small gas engines is negative about the use of ethanol in what they're working on or with. Unfortunately, I have no sources to sight for the above second or third hand information.
Not only that; while it has been touted as a pollution reduction measure, it has also been "sold" to us as a fuel supply extender despite the fact that it's use reults in a reduction of gas mileage in virtually every vehicle. Follow the money. Whose cronies and donors are getting fat selling ethanol? 
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By charliemccraney - 12 Years Ago
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I have yet to experience anything negative related to ethanol.
Regardless, he's been running the same carbs for years so it's probably not related to ethanol in the fuel as it would be nothing new.
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By pegleg - 12 Years Ago
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Charlie, Maybe, but the ethanol seems to be hard on accel. piston rubber and Viton needles. So i'm wondering Dennis if you've checked fuel pressure and for sticking needle. I run brass ones in mine just because, and I have had trouble with the needles and pistons getting soft and sticking.
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By speedpro56 - 12 Years Ago
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Frank, I've had the same problem with ethanol making the needle seat stick. I suppose that's why ford dealerships offer ethanol treatment products now as well as auto parts stores.
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By pintoplumber - 12 Years Ago
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I got the timing cover back on tonight. Cam was timed right. Should be able to finish tomorrow and start it.
The carbs all have fuel, I loosened the linkage and tried each carb separately and the motor rev'ed.
I'll try it on the center carb only tomorrow. The ford race at Maple Grove is this weekend, I hope I can get it running.
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By The Horvaths - 12 Years Ago
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Do yourself a favor and break out the ignition timing light before you tear into the carbs.
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By DANIEL TINDER - 12 Years Ago
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[quote]pegleg (8/12/2013)
Charlie, Maybe, but the ethanol seems to be hard on accel. piston rubber and Viton needles.
For what it's worth, I haven't had any needle or accel. pump issues since I quit using Sta-bil (tip I got from a Pony Carb. tech). There are usually enough dry days over the winter to allow cycling of old gas, and topping off with fresh.
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By The Master Cylinder - 12 Years Ago
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DANIEL TINDER (8/13/2013)
There are usually enough dry days over the winter to allow cycling of old gas, and topping off with fresh.
Which bring up a point. Dennis, how old is the gas in your tank? The "New and Improved" gas of today with ethenol likes to absorb moisture and doesn't 'stay fresh' as gas of the past. just trying to think outside the box...
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By glrbird - 12 Years Ago
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Dennis
Pegleg is on the right track, put a fuel preasure gauge on it if you dont have one. check the preasure when the engine starts to have problems. Weak fuel preasure can cause a lot of problems.
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By NoShortcuts - 12 Years Ago
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'The Master Cylinder' makes a good point regarding the nature of ethanol to absorb moisture over time. Another issue that can occur with vehicles that sit for a period of time between uses (fire trucks) is phase separation.
I was interested in the comment from Daniel regarding the use of Sta-Bil fuel additive. Unfortunate that Pony Carburetors has closed...
I'm with Gary B. and Frank regarding problems with Viton needle and seats, and the possibility of problems with accelerator pump pistons with the 3x2 set-ups. I've had friends that have had other rubber (neoprene) parts [hoses, diaphragms] softened by ethanol, too. -Some of the advertisers of carburetor and fuel pump rebuild kits are now hyping that their components are ethanol compatible.
As Gary Ryan suggested, I also would recommend checking fuel pressure. With the 3x2 set-up, you likely have a pressure regulator and gauge immediately adjacent to the carbs. -Probably set for about 3 p.s.i.? It might be good to disconnect the fuel line from the output side of the fuel pump and check fuel flow rate and output pressure. Again, ethanol can damage the pump diaphragm.
'The Horvaths' suggestion regarding using a timing light to check initial timing and timing advance is a good one, too. I know everything ran okay before the rebuild, but IF the timing curve is malfunctioning for any reason, it could torpedo engine performance as badly as a faulty ignition coil which I mentioned previously.
Best wishes, Dennis...
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By pintoplumber - 12 Years Ago
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Some more facts.
I don't think it's a float sticking problem, I could rev the engine using the front or back carb with the linkage loose.
When I removed the engine, some of the plug wires got pinched between the firewall and bellhousing. I got new plug wires and had to put new ends on one end. I had the stumble at this point.That was the first time I started the engine. I replaced points,condenser, and distributor cap. Plugs are new with rebuild. Autolite 46.
10 degrees initial, 26 total centrifugal advance. I don't remember total advance before engine change, but I have paint marks on the timing pulley at 10 20 30 and 40. I seem to remember seeing it between 30 and 40 before.
I forgot to mention, when I go downhill and let off the gas, it backfires out the exhaust.
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By pintoplumber - 12 Years Ago
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I took it for a spin around the block this evening running on just the center carb. Still stumbles above 2500.
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By MoonShadow - 12 Years Ago
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Most engines will free rev better than under power pulls. Just reading here I'm suspicious of your fuel delivery system. Have you change your filters lately? Do you have an electric booster pump on it? Kind of sounds like not enough fuel getting to the carbs. I have to run a booster pump on my 56 with the McCullouch. Anytime I make a hard run, even with a 427 hipo mechanical pump, it would run out of fuel in second. I expect your new engine is demanding more fuel that before. Anyway thats my thoughts. Hope you get it cured soon. If not I bet it can get fixed in Columbus! Chuck
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By Klaus M - 12 Years Ago
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I have just put an rebuild 272 in my 55 F100, with an IskyE-4 cam (installed 3º advanced),large valve G-heads and running one Holley 94.I have used the original pulley from the 239 engine but under first test run I forgot that the timing mark on the pulley don’t mark TDC but 10º advance, so on my first run my initial timing was in fact around 24º advance. Just thinking if the distributor set in its advance it will get much to much advance and probably run very bad! I have tried to run the 239 distributor but that don’t work very well. I have read that the engine vacuum can change quit a lot with the cam, so now I have modified the vacuum port on the Holley and running MSD-8383 distributor. Just my experience with the E-4 cam and timing. 
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By Hoosier Hurricane - 12 Years Ago
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Dennis:
You have changed heads. What valve springs are you using? Is it possible that the valve springs are "soft"? Are they shimmed as required?
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By pintoplumber - 12 Years Ago
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John, I got the police package springs from Schuman. The timing pulley has marks at 0 and 10, my total advance is 26. Is that enough?
A couple of years ago when it was really hot at Columbus, I was running out of fuel at 3/4 track. That felt different. Now all 3 carb bowls would be full for my initial hit of the throttle.
I had gotten valves and springs from Schuman.
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By Y block Billy - 12 Years Ago
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Hi Dennis,
I think most run upwards of 36* total timing and backfiring out the exhaust when you let off is normally a retarded condition. Did you check your timing with No 1 cyl to TDC with the new crank? maybe the relation of No 1 at TDC is slightly different than the 239 crank was and your marks may be off.
Just a thought!
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By The Master Cylinder - 12 Years Ago
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Just an early morning thought. You mention you replaced the plug wires and cap. You also mentioned it backfires when coasting. Are you sure you have the right wire going to the right plug. Maybe you have two crossed and it doesn't show up until you put a load on it.
Just another 1¢ worth.
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By pegleg - 12 Years Ago
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Dennis,
Obviously you thought about this, but backfiring on the "over-run" is ty[pically a lean condition.
Could be intake (underneath) or a dist Vacuum can, or a carb gasket/ internal leak. Have you checked plugs to try to isolate it? Master could right too, a weak spark could possibly act like that.
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By The Horvaths - 12 Years Ago
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Or the ubiquitous "slipped damper ring" could indicate incorrect initial timing.
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By Hoosier Hurricane - 12 Years Ago
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Dennis:
Can you stand one more thought from me? I assume you have a hand choke on your center carb, I can't remember for sure. If so, while running on the center carb, pull the choke out a little and see if it helps, at least until it needs more air. That would at least tell you if you are lean.
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By pintoplumber - 12 Years Ago
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Y block Billy (8/14/2013)
Hi Dennis,I think most run upwards of 36* total timing and backfiring out the exhaust when you let off is normally a retarded condition. Did you check your timing with No 1 cyl to TDC with the new crank? maybe the relation of No 1 at TDC is slightly different than the 239 crank was and your marks may be off. Just a thought!
Billy, the crank is timed right with the camshaft. My machinist came over sunday to look at it since I had the timing cover off. I have another 292 crank sitting here to look at. He had a hard time believing the crank keyway wouldn't be straight up for timing it.
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By pintoplumber - 12 Years Ago
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The Master Cylinder (8/14/2013)
Just an early morning thought. You mention you replaced the plug wires and cap. You also mentioned it backfires when coasting. Are you sure you have the right wire going to the right plug. Maybe you have two crossed and it doesn't show up until you put a load on it.
Just another 1¢ worth.
We're wired up right. A couple of years ago I had 7 and 8 reversed at the engine, boy does the exhaust really crack loud that way.
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By pintoplumber - 12 Years Ago
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pegleg (8/14/2013)
Dennis,
Obviously you thought about this, but backfiring on the "over-run" is ty[pically a lean condition.
Could be intake (underneath) or a dist Vacuum can, or a carb gasket/ internal leak. Have you checked plugs to try to isolate it? Master could right too, a weak spark could possibly act like that.
Frank,I too thought the backfiring comes from a lean condition. Could the G heads be flowing that much better that I'm running lean? I'm thinking I need to increase jet sizes. I have .53 in the center and .51's on the outer ones.
I'm sure the intake isn't leaking at the heads, I've sprayed starting fluid around the base using the little straw that comes with a can of carb cleaner.
I'm running centrifugal advance only.
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By pintoplumber - 12 Years Ago
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The Horvaths (8/14/2013)
Or the ubiquitous "slipped damper ring" could indicate incorrect initial timing.
The 239's don't have a damper, just a pulley with timing marks on it. I'm sure it's timed right.
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By charliemccraney - 12 Years Ago
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Are you determining that it is timed right with a degree wheel?
During my second build of the engine, the cam was almost 10 degrees retarded in the straight up position. That was with the same cam and timing set. Unfortunately, I never checked the previous build so I can't know if it is the crank or cam or timing set that is so far off.
If you're going based on where it was with the old crank, you're probably not timed the same because of manufacturing tolerances. And if you changed the cam or timing set, I can almost guarantee that you are not. I don't know if that could make it bad enough to cause problems, though.
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By MoonShadow - 12 Years Ago
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Try setting the timing by ear. I'm assuming you know how. Mark the current timing advance point. Then see how close the sweet spot and the timing mark are. Its a quick check. I mentioned earlier that with the increase in cubic inches and other changes you could be running lean. Does it act sort of like a fuel pump going bad? Misses and backfires under load? Chuck
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By pintoplumber - 12 Years Ago
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Hoosier Hurricane (8/14/2013)
Dennis:
Can you stand one more thought from me? I assume you have a hand choke on your center carb, I can't remember for sure. If so, while running on the center carb, pull the choke out a little and see if it helps, at least until it needs more air. That would at least tell you if you are lean.
I think I can try that. The engine is running faster at idle now since the spring tension from the other 2 carbs isn't holding the butterfly shut tight.
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By pintoplumber - 12 Years Ago
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charliemccraney (8/14/2013)
Are you determining that it is timed right with a degree wheel?
During my second build of the engine, the cam was almost 10 degrees retarded in the straight up position. That was with the same cam and timing set. Unfortunately, I never checked the previous build so I can't know if it is the crank or cam or timing set that is so far off.
If you're going based on where it was with the old crank, you're probably not timed the same because of manufacturing tolerances. And if you changed the cam or timing set, I can almost guarantee that you are not. I don't know if that could make it bad enough to cause problems, though.
Charlie, I used a degree wheel. It took me a long time to understand what I was doing. Every time I did it I'd come up with a different number. I walked away from it for 2 weeks. Then I was getting consistent numbers. I talked with Ted and I ended up using the 2 degree retarded keyway which gives me 3 degrees advance.
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By pintoplumber - 12 Years Ago
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MoonShadow (8/14/2013)
Try setting the timing by ear. I'm assuming you know how. Mark the current timing advance point. Then see how close the sweet spot and the timing mark are. Its a quick check. I mentioned earlier that with the increase in cubic inches and other changes you could be running lean. Does it act sort of like a fuel pump going bad? Misses and backfires under load? Chuck
Chuck, the exhaust is too loud to hear pinging. I only ever heard some pinging when I was towing the camper last year. I don't have the blackness on the plugs like when I'd have to change them to race. I must have 8 sets of plugs for the old heads.
I've got through a tank of gas since the end of june, that should have showed up on the plugs.
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By Pete 55Tbird - 12 Years Ago
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Try a Google search of backfire vs afterfire ( popping in the exhaust system) this is caused by a RICH fuel condition from unburned gas in the exhaust. Check the ignition and ignition timing. How do the plugs look? Pete
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By pegleg - 12 Years Ago
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Pete, Yup. OR a misfire which dumps unburned fuel into the exhaust where it fires. Been there, done that.
Dennis, I don't think so. Bigger ports might just make it Lazy down low, but they should (obviously) work better higher up. Maybe the Advance can leaks? You read plugs yet? could be Jetting, but that's pretty severe. usually they'll surge when they're too lean on the mains, or the floats are set too low.
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By PF Arcand - 12 Years Ago
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Dennis: I have no idea why your having the current problem..but an issue to look at later, is that you state that your new engine is like the old 239, it has no crank damper. Might want to get some expert advice (from someone like Ted?) on that point, especially since you race your truck. Ford put dampers on the later engines for a reason..
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By NoShortcuts - 12 Years Ago
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Well, Dennis, you've got us all scratching our heads. Based upon all that has been discussed to date, consider going at this in a different way. Locate a vacuum gauge. Hopefully, you’ve got enough running time on the engine that you’re comfortable dropping the engine idle speed down to ‘normal’. The numerical ‘normal’ vacuum gauge reading on your engine will likely be lower than an everyday grocery-getter because of the Isky E-4 cam you’re running. -Your cam probably has about 40 degrees of valve overlap. Sooo… In doing vacuum gauge readings, the action of the gauge needle will generally be more telling than the numerical gauge reading.
Run your engine until it is at operating temperature. Connect the vacuum gauge to the intake manifold.
At engine idle speed, what is the movement of the needle indicator? -is the vacuum gauge needle steady?
-does the needle drop 1-7 inches at regular intervals?
-is there a sharp, intermittent drop of the needle? -does the needle drift either side of your 'normal' reading? -if the needle does drift either side of your ‘normal’, how many inches does it drift each way? -what is the numerical reading of the vacuum gauge at idle? -what is your idle speed?
At a steady engine operating speed of 2000 rpm, what is the movement of the needle indicator?-does the needle fluctuate rapidly at this engine speed? -if the needle does fluctuate rapidly, what numbers does it fluctuate between? -if there is such a fluctuation, does the fluctuation amount increase as the engine speed is increased?
I’m in hopes that this test will tell us something we don’t know. 
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By charliemccraney - 12 Years Ago
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Do you have a bigger intake to try just to rule it out?
I wonder if the secondary carbs need to open sooner. Using an online airflow calculator, your 283 requires about 164cfm @2500rpm. Everything else being the same, that's about 10% more than before, and 20% more than the 239. I think when Ted was doing the 3-2 dyno testing, he said they flow about 150cfm each. If I'm remembering that correctly, then you may be exceeding the limits of a single carb which is why you have the stumble with only one carb and all 3, if the other 2 have not yet begun to open.
I can bring my B intake and an Edelbrock 600 to Columbus for you to try if you like. I can also bring my points distributor, but aren't you running the 239 drive gear?
The Edelbrock didn't like my engine combo, the air valve wasn't right for it but that doesn't mean it wouldn't work for you. I would get a stumble with it but it was at a much higher rpm.
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By pintoplumber - 12 Years Ago
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NoShortcuts (8/15/2013)
Well, Dennis, you've got us all scratching our heads. Based upon all that has been discussed to date, consider going at this in a different way. Locate a vacuum gauge. Hopefully, you’ve got enough running time on the engine that you’re comfortable dropping the engine idle speed down to ‘normal’. The numerical ‘normal’ vacuum gauge reading on your engine will likely be lower than an everyday grocery-getter because of the Isky E-4 cam you’re running. -Your cam probably has about 40 degrees of valve overlap. Sooo… In doing vacuum gauge readings, the action of the gauge needle will generally be more telling than the numerical gauge reading.
Run your engine until it is at operating temperature. Connect the vacuum gauge to the intake manifold.
At engine idle speed, what is the movement of the needle indicator? -is the vacuum gauge needle steady?
-does the needle drop 1-7 inches at regular intervals?
-is there a sharp, intermittent drop of the needle? -does the needle drift either side of your 'normal' reading? -if the needle does drift either side of your ‘normal’, how many inches does it drift each way? -what is the numerical reading of the vacuum gauge at idle? -what is your idle speed?
At a steady engine operating speed of 2000 rpm, what is the movement of the needle indicator? -does the needle fluctuate rapidly at this engine speed? -if the needle does fluctuate rapidly, what numbers does it fluctuate between? -if there is such a fluctuation, does the fluctuation amount increase as the engine speed is increased?
I’m in hopes that this test will tell us something we don’t know.
I'll put a gauge on it when I get a chance. Had a viewing last night, model rr club tonight, another viewing friday night and the funeral sat.
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By pintoplumber - 12 Years Ago
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charliemccraney (8/15/2013)
Do you have a bigger intake to try just to rule it out?
I wonder if the secondary carbs need to open sooner. Using an online airflow calculator, your 283 requires about 164cfm @2500rpm. Everything else being the same, that's about 10% more than before, and 20% more than the 239. I think when Ted was doing the 3-2 dyno testing, he said they flow about 150cfm each. If I'm remembering that correctly, then you may be exceeding the limits of a single carb which is why you have the stumble with only one carb and all 3, if the other 2 have not yet begun to open.
I can bring my B intake and an Edelbrock 600 to Columbus for you to try if you like. I can also bring my points distributor, but aren't you running the 239 drive gear?
The Edelbrock didn't like my engine combo, the air valve wasn't right for it but that doesn't mean it wouldn't work for you. I would get a stumble with it but it was at a much higher rpm.
Charlie,
I have 3 B intakes, but no carbs. I also have an offy 3x2 with big ports, but Ted suggested using the edelbrock.
Yeah, I have the 13 tooth gear on mine.
I have a spare 292 that still has the distributor in it, and a complete 239 that I could use the gear and make up another distributor combo.
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By pintoplumber - 12 Years Ago
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I got a chance to get a vacuum reading. At 500 rpm it would bounce between 11-12. At 750 rpm 13-14. At 1200 16 and steady. At 2000 17 and steady. When I would blip the throttle it would just touch the outer carb butterflies a hair. It would dip down to 5 and up to 22 when it snapped shut.
I'm thinking more and more it's carbs. The intake sat on the shelf for 4 months.
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By charliemccraney - 12 Years Ago
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I think your vacuum is low. I get 15 at about 750rpm, with a little bigger cam. Do you know what it was with the previous build?
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By pintoplumber - 12 Years Ago
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I seem to remember 13 and 17 from the old engine.
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By pintoplumber - 12 Years Ago
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Progress! I talked to a retired mechanic at the funeral today. He suggested changing one jet in each carb.
I had .53 in the center carb and .51 in the front and rear. I put one .57 in the front and one .57 in the rear.
I still had a stumble sometimes around 2500 but when I got over that it was pulling nicely in 3rd gear up a long hill. I let off at 3500, felt I was going fast enough. I think I'll try putting the other two .57 jets in and try again.
Like it is, I should be able to go to the ford race at Maple Grove tomorrow.
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By pegleg - 12 Years Ago
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Good, glad to hear it
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By pintoplumber - 12 Years Ago
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Well two .57's front and rear were too much. I have to go back to .57 and .51 front and rear.
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By NoShortcuts - 12 Years Ago
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Hi Dennis, Slow on my reply to your supplied info. From your most recent posts, I’m scratching my head that all of this is about carburetor jetting…
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In suggesting that you take engine vacuum gauge readings, my first questions were about the movement of the needle indicator at engine idle speed. Based upon what you have observed and reported at your ‘normal’ idle speed of 500 rpm, I would rule out: -leaking valves (would see the needle periodically drop 1 to 7 inches at regular intervals if leaking) -sticking valves / valve guide problem (would see rapid,intermittent drop of needle each time a valve was supposed to close) -excessive valve guide clearances (would see a low reading and needle fluctuations of up to 3 inches either side of your engine’s ‘normal’ reading) -too rich an air fuel mixture at idle (would see needle indicator drift back and forth) -too lean an air fuel mixture at idle (would see an irregular drop of the needle) Comments: -I’m surprised that your engine vacuum reading is 11 at an idle of 500. To me, with what I believe an Isky E-4 camshaft grind to be like, this seems LOW. Because of the valve overlap interval of this cam, I would expect the engine vacuum reading to be at least 14 inches at 600 rpm. Without a damper on the vacuum gauge, the 1 inch swing of the needle that you report with the E-4 cam is probably normal. However, the 11 you’re getting at idle makes my eyes squint and my face wrinkle in skepticism.I’m of the thinking that the steady but low vacuum reading you are reporting is attributable to: -late ignition timing -valve stem to rockerarm clearance settings being too small (I’m sure that in your case this is not a consideration) -late valve timing SUGGESTED FOLLOW-UP TEST – Try advancing the ignition timing with the engine at idle. IF the vacuum gauge reading does not increase to a higher number, I believe the valve timing (camshaft installation) to be incorrect. ___________________________ My second set of questions was about engine vacuum when the engine was held at a steady operating speed of 2000 rpm. Based upon the steady vacuum reading of 17 that you reported at 2000 rpm, I would rule out: -valve spring retainer heights being excessive or not uniform (vacuum readings would fluctuate rapidly if retainer heights were incorrect or different from each other. Reasoning: spring pressures would vary if assembled heights were different, just as if you had weak valve springs. Again, your springs are new and spring values are not in question.) I’m surprised that your engine vacuum is only 17 at 2000 rpm. Again, this seems low to me. Once again, I question ignition timing or valve timing (camshaft sync to the crankshaft) Not reported: -You did not indicate if the vacuum reading remained steady at 17 or if the needle fluctuated as you increased engine speed above 2000 rpm. ___________________________ I did not suggest your closing the throttle quickly at 2000 rpm because I expected that your piston rings are not seated yet. The reading you got when you did this indicates that while your piston rings may not be fully seated, they’re doing their job just fine anyway.
___________________________ I hope someone else will share their thoughts on your engine’s idle speed vacuum reading of 11 and 17 at 2000 rpm. I see Charlie's questioning your low rpm vacuum readings, too.
I’ll be interested to hear how this finally shakes out. Regards,
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By Ted - 12 Years Ago
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Gut feel says fuel demand went up with the increase in cubic inches. Where the 239 may have been on the verge of being over-carburetted, the new combination is now requiring more cfm thus needing larger jets to get back to that ideal air/fuel ratio. This is a catch twenty-two when it comes to jetting though as adding carbs that were originally designed to be used singularly has those carbs being reduced in cfm which in turn requires smaller jetting. As a general rule, when power valves are blocked off, larger jets are required in which to compensate. It’s still important that the end carbs be jetted the same though without a difference in jetting between the front and rear carbs. You might consider the jetting on the center carb also.
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By pintoplumber - 12 Years Ago
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We got rained out at Maple Grove today. On the way back on the 4 lane highway I ran it from 2000 up to 4000. A little bit of hesitation around 2500, but ran good up to 4000. Sounds like I should increase the center carb jets too.
Next sunday is the ford race at Mason Dixon.
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By NoShortcuts - 12 Years Ago
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pintoplumber (8/17/2013)
Progress! I talked to a retired mechanic today. He suggested changing one jet in each carb.
I had 53s in the center carb and 51s in the front and rear. I put one 57 in the front and one 57 in the rear.
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pintoplumber (8/18/2013)
Well two 57's front and rear were too much. I have to go back to one 57 and one 51 front and rear.
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Dennis, both high speed jets need to be the same in each front and rear carburetor. Each high speed jet feeds a different set of cylinders.
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By pintoplumber - 12 Years Ago
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I have a limited number of jets on hand, I think I'm going to get 3 pairs of .54's.
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By yalincoln - 12 Years Ago
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find someone to bore the carb out to 1&3/16 like they did in the old days and jet them up!!! good luck.
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By pintoplumber - 12 Years Ago
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I drilled out two pairs of .48's and one pair of .51's to .54 so I have three sets of .54's. Put them in today and they ran worse. I have to drive about two miles to get home after getting on it before I can check the plugs. 1 and 5 looked the blackest - not the porcelain but inside the plug. I have some .53's and .52's to try next.
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By pintoplumber - 12 Years Ago
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Well, all the wise men in Columbus helped me get the truck running without missing. It wasn't the jets. Rotor and points. I'll post a picture when I get home. I'm doing this with a kindle and am limited.
I need to go back to smaller jets tomorrow.
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By The Horvaths - 12 Years Ago
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Did a timing light tell the story?
Great to hear that it's back to good health.
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By pintoplumber - 12 Years Ago
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Harry noticed the distributor cap moving at idle. When we pulled the cap off, the top tab on the rotor was burned off. Put the old one back on and he said it fit too loose. Put some masking tape on the shaft and then put the rotor on. Closed the point gap a little.
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By NoShortcuts - 12 Years Ago
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GooD GrieF, Dennis! I don't recall your mentioning an ignition miss, too. After your previous reports of how the engine was running with your jetting efforts, I'm surprised that you were able to make the trip.
Anyway, from the peanut gallery, I'm still scratching my head regarding the low vacuum readings that you reported at idle speed and as you increased the engine rpm up to 2,000.
You are in the company of a large contingent of wise men at Columbus. Certainly individuals like Ted Eaton, Jerry Christenson, and Harry Hutton, to name only a few, should have a sense of what is to be expected with the cam profile that you're running and the camshaft timing orientation you have effected. I have never messed with advancing or retarding the camshaft event in relation to the crank.
Thanks for the update on getting the tuning of your new build sorted out.
Best Wishes...
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By pintoplumber - 12 Years Ago
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I ran an 18.05 against Ted , hitting the brakes at the finish line because I beat him to the finish line. Only thing is I dialed an 18.70. I'm sure I'm in the 17's now it's running great.
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By pintoplumber - 12 Years Ago
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NoShortcuts (8/31/2013)
GooD GrieF, Dennis! I don't recall your mentioning an ignition miss, too. After your previous reports of how the engine was running with your jetting efforts, I'm surprised that you were able to make the trip.
Anyway, from the peanut gallery, I'm still scratching my head regarding the low vacuum readings that you reported at idle speed and as you increased the engine rpm up to 2,000.
You are in the company of a large contingent of wise men at Columbus. Certainly individuals like Ted Eaton, Jerry Christenson, and Harry Hutton, to name only a few, should have a sense of what is to be expected with the cam profile that you're running and the camshaft timing orientation you have effected. I have never messed with advancing or retarding the camshaft event in relation to the crank.
Thanks for the update on getting the tuning of your new build sorted out.
Best Wishes...
I didn't know I had an ignition problem. It ran fine up to 2500 rpm's. It missed or died after that and I figured it was when the outside carbs came in.
The truck gets trailered if the race is far away.
Billy's brother Dan, when he heard me get on it said you'd better check the points. Between that and the rotor problem I think most of the problem was electrical. I put the smaller jets back in this morning.
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By Klaus M - 12 Years Ago
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hi, iam stating to put together 3x2 setup for my 272 and i have a few questions ,what jets size are you running now? How about the power valve in the center carb??
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By pintoplumber - 12 Years Ago
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Klaus, I have .53 jets in the center carb. In the end carbs I have a .51 and .52 . I have plugs in the end carbs power valve holes. A 6.5 power valve in the center carb.
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