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.

  Dennis in Lititz PA

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

"The Master Cylinder"

Enjoying life at the beach in SOCAL

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...

NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

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.

  Dennis in Lititz PA

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.

  Dennis in Lititz PA

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.

John - "The Hoosier Hurricane"

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.

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

What?

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.

NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

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?