|
By davecole - 13 Years Ago
|
I was having problems with the engine idling sporadically on my 292 with 2 bbl autolite and fordomatic transmission.
I bought a used carb from a 352, soaked it in carb cleaner overnight and rebuilt it. The jets in the 352 carb were 55 and the jets in the 292 carb were 46 so I swapped them when I rebuilt it. After soaking the carb, I ran a wire through each passage and sprayed each passage with spray carb cleaner and then compressed air. I put the carb on the engine and it fired up nicely, it has a rough idle, but runs great other than that. I tried adjusting the idle after the engine warmed up and the choke was wide open.
The driver side adjustment can be adjusted all the way in. It still runs, but not as good, and sounds different. The passenger side screw can be adjusted all the way in with no change at all. I can also adjust both screws way out past 1.5 turns with no change. I sprayed wd 40 all around the base with no change. I also sprayed it around the throttle shafts with no change in idle. The transmission shifts fine.
Does anyone have any ideas of why my idle screws don't seem to have much affect on the idle? Thanks.
|
|
By charliemccraney - 13 Years Ago
|
|
On a Holley, it can indicate a bad power valve. Do Autolites have power valves?
|
|
By davecole - 13 Years Ago
|
|
Yes, it has a new power valve that came in the carb kit. The carb kit is the same for a 352 carb and a 292 carb, so it is the correct power valve also.
|
|
By charliemccraney - 13 Years Ago
|
New does not always equal good. It wouldn't hurt to check it.
Another thought, because the carb was originally for another application, maybe the throttle plate is open too far in order to get the desired idle rpm and activating the main circuit, in which case the idle screws will do little.
|
|
By davecole - 13 Years Ago
|
|
How do I test the power valve?
|
|
By gekko13 - 13 Years Ago
|
|
Dave, there are several iterations of the Autolite 2 bbl so randomly swapping applications may cause some problems. I have also found some kits are not very good. I recommend only NAPA/Echlin or Standard Hygrade kits. There may be other good kits but those are the ones I have had satisfactory results with. It does sound like the power valve is either blown, not installed properly or the wrong vacuum value. There are about 6 commonly available power valves. Each has a number stamped into it that identifies the vacuum at which it opens. Examp. "65" = 6.5 inches of Hg (mercury). A number 65 is stock in most applications. Check the float level. Hopefully the float valve in your kit is Viton tipped. The plain tipped ones often leak. A good fuel filter is also essential. Be sure that there are no vacuum leaks elsewhere. Good luck and let us know what you find.
|
|
By davecole - 13 Years Ago
|
|
I decided to rebuild the original 292 carb (for the third time), and use the best parts from both carbs with the exception of the jets and venturi assembly, which I used from the original carb. I thoroughly checked every circuit to make sure they were all clear. I also sprayed carb cleaner through every circuit and every air bleed, etc. I made sure the throttle and choke plates were closing correctly, by loosening the screws that hold them in place and wiggling them while closing them, and then tightening them in place. They all close nice and flush. I made sure the float level was correct. I used the power valve from the 292 carb which had a new power valve put in a few months ago. I put everything back together and the car runs great. It has a fairly nice idle and and no hesitation when punched. But, when I went to adjust the idle, I can screw both idle mixture screws in all the way, and when I do the engine speeds up and appears to smooth out a little more. When I adjust them back out some it runs rougher but not bad at all. When I continue to adjust them out further than 1.5 turns, all the way to 3.5 turns, it doesn't get any worse... just stays the same. I don't know why adjusting the idle mixture isn't doing what it is expected to do, or if I should even do anything about it because the engine runs so good as it is. Any ideas?
|
|
By oldcarmark - 13 Years Ago
|
|
If you can seat both idle mixture screws and it keeps running the carb is drawing fuel from another circuit.Possibly you have a vacuum leak somewhere.After doing the carb twice with no improvement you need to look again for another problem.Try squirting some quick start around the intake and carb mounting.If the idle speed increases you have a vacuum leak.If the idle speed screw is holding the throttle plate open more than about 1-1 1/4 turns after the screw contacts the throttle plate lever you are drawing fuel from the transition circuit which comes in after you leave idle.When you start drawing fuel from the transition circuit the idle mixture screws have no effect.Excessive throttle plate opening is another indication of a possible vacuum leak.
|
|
By gekko13 - 13 Years Ago
|
|
It sounds as though the engine is "idling" on the main circuit. Note that if the throttle blades are too far open the idle ports will not be exposed to enough manifold vacuum to function properly. Fuel will flow from the boosters and circumvent the idle system. Also, the booster venturi has a fixed idle air bleed orifice built into it which is application specific. You changed that and altered another parameter. If possible, verify manifold vacuum at idle with a guage. If it is low, < 10" of Hg, you will need to determine why and correct that before you can proceed with the carb.
|
|
By lowrider - 13 Years Ago
|
|
Just a thought on the power valves. Sometime people will install a power valve from a Holley in an Autolite carb. While it will screw in ok, it may only work for a short time if at all. The difference between the 2 is the Holley has a recess where the gasket seats and the Autolite is flat. In the end the gasket doesnt seal & it leaks fuel like a blown power valve.
|
|
By Ted - 13 Years Ago
|
|
As has been mentioned, checking for vacuum leaks is at the top of the list. As a general rule, always go with the jets that come in a given carb as a baseline. Jets sizing is more of a function of carb size and air bleeds and not so much as based on the cubic inch. The venturi assemblies in the Autolite carbs are notorious for becoming warped due to over-tightening. Because the air bleeds for the idle mixture is at the outside edges of the venturi assemblies, the idle mixture adjustment ends up being compromised when warpage is present. If you do check that for straightness and find the gasket surface is less than straight, then the simple fix for this is to put a double gasket under the assy.
|
|
By peeeot - 13 Years Ago
|
A note about checking power valves that I didn't see anyone else mention: when you remove the power valve cover it should be bone dry with no evidence of fuel having been present. If fuel moisture is present it means leakage past the power valve gasket or diaphragm. I have used GP sorensen gasket kits almost exclusively and I know there were a couple of power valve gaskets included; not all of them would work properly with the actual valve included.
Perhaps you covered this when you say you sprayed carb cleaner through every opening, but when rebuilding I like to spray water through the paths air and fuel should take. If I don't see a nice stream of water coming out of anyplace it should, I don't move forward until I do. Following that up with compressed air is a good idea of course. One time I had an air bleed on a 4100 that I had to remove the top plug to clear up.
Ted: wouldn't double-gasketing a booster assembly effectively raise the location of the fuel holes relative to the level in the bowls, and thus affect the desired float setting? Or is it not that sensitive?
|
|
By davecole - 13 Years Ago
|
Thanks for all the tips. I would like to clear up a few things. The original carb that I am using has the original venturi assembly and original jets. I have two power valves from two different kits and neither solved the problem. From the description I was given regarding how the gasket sits on it, it is not a Holley power valve. The power valve is dry under the cover. The idle speed adjuster screw was turned less than one turn after contact with the throttle shaft lever. The car idle rpms are very low, probably at the correct setting or even a little lower. When I come to a stop, I can barely tell the engine is running except for the slight roughness. The float level is set perfect, but I still need to check the gas level in the bowl. I have checked for leaks by spraying wd 40 around the carb base and the throttle shafts, but will try it again with starting fluid. I am positive that all the circuits are not clogged.
So now I will recheck for a vacuum leak by using starting fluid instead of wd40. To keep the mist from entering the carb through the top, I will put the air cleaner housing on and then spray the base. I will also check the manifold vacuum. I have a gauge. Where is a good place to take the reading. This is a 62 292 engine if that helps. Could burnt valves cause bad vacuum? I don't know the condition of the valves. I'll check to see if the venturi assembly is not warped. I will also check the timing, dwell, and set the idle rpm to factory specs. Does anyone know what that is?
It might be a few days before I get all this done because of my job, but I will do these things. Even though it is running pretty good the way it is, I want it to be right. I am learning a lot with your help, but what I don't get is what does the power valve have to do with the idle? I thought it only was used during acceleration. Also, if there was a vacuum leak, would it affect the transmission? The transmission shifts perfectly and the kickdown also works perfectly. The car has manual brakes, so I think there is nothing else using vacuum.
Thanks for all your help.
|
|
By oldcarmark - 13 Years Ago
|
|
A vacuum gauge is a great tool for diagnosing engine condition.If you still have the printed instructions there should be examples of various readings on the gauge.Sounds like you have the idle speed screw in the correct range.
|
|
By rmk57 - 13 Years Ago
|
|
It may be too much of the idle transfer slot is exposed. Take the carb off and close off the idle screw so the transfer slot is square with the throttle blade. Install carb again and try adjusting mixture screws.
|
|
By peeeot - 13 Years Ago
|
According to carnut.com, your initial advance should be set at 12* with the automatic transmission for a '62 292. Dwell angle is 26-28* (point gap of 0.015"). I would assume the idle speed to be approximately 500 rpm with the trans in drive.
As for your question about the power valve, it is not an idle control device, but since one side of the diaphragm is exposed to manifold vacuum, the potential exists for unmetered fuel to be drawn through a leaky diaphragm or gasket. Such a leak would enrich the mixture at idle, perhaps enough so that no additional fuel is needed from the actual idle circuit, which could explain why the engine is able to run with the mixture screws closed. It would not run as smoothly as it should in that case, however, because the idle circuit bleeds air into the fuel stream and mixes it a bit before it ever gets to the mixture screws. A leaky power valve would not provide that "pre-mix" so the mixture uniformity would suffer as would idle quality.
Have you verified that the mixture screws are in fact fully seating?
Assuming your trans has a vacuum modulator, the transmission shift qualities probably wouldn't be affected by the kind of vacuum leak we're talking about here, but if the modulator is leaky, THAT could affect the carb adjustments. It'd be worth plugging the modulator vacuum line just to check whether it's a factor.
|
|
By Ted - 13 Years Ago
|
|
peeeot (12/17/2012)
....... Ted: wouldn't double-gasketing a booster assembly effectively raise the location of the fuel holes relative to the level in the bowls, and thus affect the desired float setting? Or is it not that sensitive?The air bleeds are not that sensitive to height changes and even if they were, the float level could be adjusted in which to compensate. A single gasket for the venturi assembly is only marginally thick (0.025”?) so double gasketting in this case is not an issue.
|
|
By davecole - 13 Years Ago
|
|
rmk57 (12/17/2012)
It may be too much of the idle transfer slot is exposed. Take the carb off and close off the idle screw so the transfer slot is square with the throttle blade. Install carb again and try adjusting mixture screws.
I don't know what the transfer slot is. I also don't know what you mean by closing off the idle screw. If I can figure out what that means, I will surely try it.
|
|
By davecole - 13 Years Ago
|
|
peeeot (12/17/2012)
According to carnut.com, your initial advance should be set at 12* with the automatic transmission for a '62 292. Dwell angle is 26-28* (point gap of 0.015"). I would assume the idle speed to be approximately 500 rpm with the trans in drive.
Thanks for the info. I will check them.
As for your question about the power valve, it is not an idle control device, but since one side of the diaphragm is exposed to manifold vacuum, the potential exists for unmetered fuel to be drawn through a leaky diaphragm or gasket. Such a leak would enrich the mixture at idle, perhaps enough so that no additional fuel is needed from the actual idle circuit, which could explain why the engine is able to run with the mixture screws closed. It would not run as smoothly as it should in that case, however, because the idle circuit bleeds air into the fuel stream and mixes it a bit before it ever gets to the mixture screws. A leaky power valve would not provide that "pre-mix" so the mixture uniformity would suffer as would idle quality.
Is there a way to test the power valve?
Have you verified that the mixture screws are in fact fully seating?
It is possible that the springs were completely compressed before the idle screw fully seated. I will check to make sure.
Assuming your trans has a vacuum modulator, the transmission shift qualities probably wouldn't be affected by the kind of vacuum leak we're talking about here, but if the modulator is leaky, THAT could affect the carb adjustments. It'd be worth plugging the modulator vacuum line just to check whether it's a factor.
I will add that to my list of things to test. I probably could also hook my vacuum gauge to wherever the transmission vacuum line goes into the motor for my vacuum test.
Thanks for all the tips and information.
|
|
By Ted - 13 Years Ago
|
|
davecole (12/18/2012)
.... Is there a way to test the power valve?Yes. While peeeot has already mentioned that any evidence of gasoline or wetness present on the vacuum side of the diaphragm is a good indicator of either a leaky gasket or ruptured diaphragm, there are testers available that will test the power valve for both diaphragm leakage and what the actual Hg opening point actually is. Here’s a picture of the power valve tester I use.
|