292 engine with irregular rpm's
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292 engine with irregular rpm's
I have a 64 F-100 with a 292 that recently began to idle rough and even when warmed up, the rpm's "flicker". From what I've been told, this usually means an intake or exhaust leak somewhere, but I have not found any. Does anyone have anything they would recommend checking? It's most severe in colder weather, but even when warmed up, the rpm's "flicker" or surge. Any advice would be greatly appreciated. Thanks!
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Joined: Sep 2004
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From: Texas
Most likely Not an exaust leak unless it's severe. If it is, it will sound like a .50 cal machine gun firing under your hood. Otherwise, its probably a vacume or intake leak, or posably a bad choke
You can spray the base of the carb and along the edges of the intake manifold with starter fluid with the engine running. when the fluid finds the leak, the RPMs will either increase, or smooth out. If that doesn't find it, try plugging off the vavcume lines to the distributor, PCV, and break booster if you have one.
Someone who knows 292 carbs can better explain choke troubles.
You can spray the base of the carb and along the edges of the intake manifold with starter fluid with the engine running. when the fluid finds the leak, the RPMs will either increase, or smooth out. If that doesn't find it, try plugging off the vavcume lines to the distributor, PCV, and break booster if you have one.
Someone who knows 292 carbs can better explain choke troubles.
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Thanks. Will try again tonight. I have a standard 600 cfm manual Edelbrock carb, which has given no problems for several years. I'm betting on an intake leak as well, I just need to find it. Thanks for the advice.
Post Fiend
Joined: Sep 2004
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From: Near Fresno, California
I would not use starter fluid - it is explosive. I have used WD40 and that works, or cracked the ox valve on my torch.
It could also be a bad spark plug or wire - why not remove a wire at a time and see if you can identify a cylinder that is not firing?
It could also be a bad spark plug or wire - why not remove a wire at a time and see if you can identify a cylinder that is not firing?
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Put new intake gaskets on....same problem. Isn't flickering or surging as much once it's good and warm, however, under any heavy acceleration it bogs down and then jumps up the rpms and smooths out. I'm guessing it's carb related. I've checked the plugs and wires and all appears to be fine there. What should I look for in the carb that would cause this? It's not as bad once its warm. Could it be a bad gasket? or stuck floats? Thanks for all the advice thus far.
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Postmaster
Joined: Dec 1999
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From: Connecticut
I'd vote for a carb overhual, since you replaced the intake gaskets. Pull the carb off and remove the bottom cover under the fuel bowl and see if the economizer valve is bad. If there's fuel in there when you take the cover off, it's blown. Have you adjusted the carb at all? Try setting the 2 mixtures screws at 1-1/2 turn out and see how it runs. What condition were the plugs when you removed them? THey should a light gray-brown color. If black, then it's running too rich and the truck could be running way to rich.
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Just to add confusion, have you checked the valve adjustment? If the lash is too loose, it will stumble and sputter at low RPM and smooth out at the higher RPM's sort of like having a cam that is way oversized for your engine. I can tell you that it drove me nuts figuring that out when I had similar problems to yours with a car I used to have.
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Here's the latest....I have found no intake or exhaust leaks anywhere, but when it's running, better yet, driving under a heavy load and I let off the gas, it's sputters a little and you can hear some slight backfire(pressure). Currently, I have been into the carb (edel. 1405 model) and reset the floats, checked all the needles and valves, and everything appears good, but it's not running. It will turn over fine, but wont run. Here's the twist...when it's 60 -70 outside, nice and warm, it starts right up and has a slight flicker in rpms (maybe 100 rpms) and drives down the road fine. I checked the cap and rotor, and it had some pits/burn marks on two spots inside the cap. The spark plugs were pretty black except the ones on the back of the engine on both sides. They looked good and normal. I've been driving this truck daily for years, and this just started happening about 6 weeks ago. If anyone has any other advice, I would gladly appreciate it. Thanks for all your help thus far, it's been very useful.
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From: Texas
Originally Posted by wes64f100
The spark plugs were pretty black except the ones on the back of the engine on both sides. They looked good and normal.
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From: Owasso Oklahoma USA
When was the last time the valves were adjusted? These are solid lifters and require periodic adjustment to make up for wear in the valve train. Everything else could be good but if the valves adjustments are sloppy then you could get the symptoms you have described.