I have this strange issue where my tudor will idle beautifully after just a few minutes of running but once it warms up to normal operating temperatures, the idle is extremely rough to the point where you think that the car might die on you. The car however does fine driving down the road and under load but once you stop at a stoplight, the car runs terribly. I also experience a hesitation in throttle response from idle. I'm thinking it might be a cracked intake manifold that is fine when the car is cold because the crack is retracted and not letting a whole lot of air in and when the car warms up, the crack expands allowing more air in creating a lean mixture. What are your thoughts?
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Yup, sounds like a vacuum leak. Spray some MM on the intake, that will tell you if that is leaking by running good for a few seconds. -
As always make sure your basics are set to specs, points etc. What happens if you cup your hand over the air horn or using the choke plate to restrict the air flow? Does it get any better? I like to use my hand this way i can meter how much air i am letting through. By doing this it richens the mixture so if there is a vacuum leak it can sometimes help smooth it out.
Heat usually expands a crack / closes it up!3~ Tudor's & 1~ Coupe
Henry Ford said,
"It's all nuts and bolts"
"Start by doing what's necessary; then do what's possible; and suddenly you are doing the impossible."
Mitch's Auto Service ctrComment
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Ignition system was entirely overhauled 2,000 miles ago. Points are checked every 500 miles to ensure proper gap. Good and consistent spark. Again, idles great when cold and just warming up but once it's all warmed up it just will not idle smoothly. Like you said, a leak should present it self when it's cold and close up when the metal expands and closes any gaps. I'm truly stumped on this one.Originally posted by Mitch View PostComment
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I like to use an unlit propane torch to check for leaks.
BTW, I know some foreign countries call a flashlight a "torch", so then what do they call a propane torch?Comment
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After setting the basics you need to determine whether you have a spark, or a fuel issue. This can be done by using an inline spark tester, can of carb cleaner, and a fuel bowl float level tool when running. Spark and fuel are always blamed on each other and it usually turns out to be the other. How are the plugs burning?
Just some of the main things:
Running lean (vacuum leak, fuel delivery)
Running rich (weak spark, carb issue)
Weak or erratic spark ( condensor, ignition circuit issues, plate wire, or wireless plate)
Doing a diagnosis will lead you up the next trail
https://www.vintagefordforum.com/for...rmittent-spark
https://www.vintagefordforum.com/for...-and-misc-tips3~ Tudor's & 1~ Coupe
Henry Ford said,
"It's all nuts and bolts"
"Start by doing what's necessary; then do what's possible; and suddenly you are doing the impossible."
Mitch's Auto Service ctrComment
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My 56 F100 is a 272 with a Holley 4 bbl and A/T.
When the engine is cold it idles fine (900-1000 rpm).
She idles fast (1800 rpm) in Park and Neutral when it’s warmed up. But in Drive it’s normal (600-800 rpm).
Does anybody know what might cause this ?11-24-2020, 07:56 PM -
After a long drive, let's say 50 miles, my car struggles to idle well. The idle gets lopy and I have to feather it in stop and go to keep it from dying. Shorter outings it runs perfect, even at full operating temp in both scenarios. Todays temp outside hovered around 90. Car ran between 150 and 160 the entire time. Even when exhibiting these symptoms.08-06-2022, 07:22 PM -
When I make aggressive throttle increases on a stationary engine, it bogs and back fires out the tailpipe, which I attribute to a vacuum leak or running too lean, or is that incorrect? Car idles fine, does it with the GAV 1/4 through 1 turn, I haven't opened it further. Intake and exhaust manifolds (new) are surfaced and true. New copper gasket at the block, new gasket at the carb and intake. I can't...01-09-2021, 04:34 PM -
I posted in the what did you do thread a couple days ago that I tuned the idle mixture with a vacuum gauge. I set the mixture to give the highest vac reading just like working on a newer car. Driving to and from work today the engine would stall if I came to a moderately quick stop. I've been running this carb for about 3000 miles now and it's never done that (and I've had some pretty hard stops)....05-18-2023, 09:07 PM -
I have never been able to get my truck to "count off" at idle but once and it would not stay running at moderate stops like that so increased the idle a bit faster. My engine is timed with a timing light and is dead on but every 8-10 seconds at idle in the garage or at a stop light you hear a little miss. Is this normal? Seems to do this only after fully warmed up as well. When it is cool...04-24-2019, 06:37 AM -
1939 Ford Deluxe Coupe, 85 hp. V8. Holley 94 rebuilt carburetor, 59000 miles showing, but odometer is not working. Non ethanol gas is used.
Heads were removed for inspection. Engine appears to have never been overhauled based on inspection of pistons and valves. Pistons and valves heavy with dry carbon. Nothing wet around piston/valves. All pistons stamped STD and do not wiggle, do...09-13-2017, 04:52 PM -
I recently disassembled, bead blasted, cleaned, and replaced all the parts included with the Renners rebuild kit for my M-S/Sears/Allstate carb. It didn’t run very well. I discovered that screwing the idle adjusting needle completely out makes the carb run great. When I return the idle screw the engine runs poorly again. So, with the idle screw out it’s getting more air and sucking less gas, a...You do not have permission to view this gallery.
This gallery has 2 photos.05-16-2020, 01:30 AM -
I am probably going to stir up a hornets nest but here goes. There is a lot of miss information on the internet and some on this site about the idle mixture adjustment needle on a Marvel carburetor. It is NOT like a Zeneth carb. On a Marvel when you screw the needle in you make the mixture leaner. To prove this to myself I first checked my plugs. They were prefect, just a light tan. I then started...11-03-2020, 01:33 PM -
I lit my A off again today. Seems to be running great. Now, how do I set the engine idle? Not the mechanical method, but at what RPM should I set the idle screw?12-10-2019, 02:23 PM -
I have a 1931 roadster which, for the most part, starts and runs great. However, after a bit of driving when it has warmed up, it begins to "chuff" (fire, fart, huff - not sure of the correct technical term) each time I shift. It isn't horrible or loud (not a backfire), but it seems like something that is likely slightly out of adjustment or that I'm not doing right with the choke or something....10-11-2017, 10:00 AM
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