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Old 10-11-2017, 08:40 PM   #1
amccarl
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Default 31 Roadster "chuffs" when shifting after it is warmed up

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 GAV. I'm not an experienced hand, having inherited this beauty from my father. Any suggestions are welcome. Thanks!
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Old 10-11-2017, 09:09 PM   #2
1crosscut
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Default Re: 31 Roadster "chuffs" when shifting after it is warmed up

Make sure your carburetor is tight to the manifold.
Check the torque of the 4 bolts that hold the manifold to the engine.
With the engine warmed up (since your problem occurs when warm) and running spray some engine starting fluid around all the edges of the manifold. If the engine speed changes you have an intake leak.
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Old 10-11-2017, 10:21 PM   #3
Mike Peters
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Default Re: 31 Roadster "chuffs" when shifting after it is warmed up

After starting your engine at full retard, are you advancing the spark lever?
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Old 10-11-2017, 10:51 PM   #4
Magicbox51
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Default Re: 31 Roadster "chuffs" when shifting after it is warmed up

My '29 Tudor has a small-ish backfire after fully warming up and when decelerating or in the process of shifting down. Maybe your "chuff" is the same thing I am experiencing, although mine is pretty noticeable because I think my muffler is also shot.

After tons of reading and searching this forum and others, I am convinced I have a leak perhaps in the junction where the exhaust pipe to the muffler clamps to the exhaust manifold and a lean mixture.

I can lessen the effect, but not eliminate it entirely by opening the GAV and making the mixture a little richer, so I am convinced of the "after-burner" effect going on in the muffler. Yours may be the same, but with a better muffler than I have.

Try opening the GAV. Normal operation is less than a turn counter-closkwise, but try it with it open more.
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Old 10-12-2017, 04:54 AM   #5
Chippy Minton
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Default Re: 31 Roadster "chuffs" when shifting after it is warmed up

Quote:
Originally Posted by Magicbox51 View Post
My '29 Tudor has a small-ish backfire after fully warming up and when decelerating or in the process of shifting down. Maybe your "chuff" is the same thing I am experiencing, although mine is pretty noticeable because I think my muffler is also shot.

After tons of reading and searching this forum and others, I am convinced I have a leak perhaps in the junction where the exhaust pipe to the muffler clamps to the exhaust manifold and a lean mixture.

I can lessen the effect, but not eliminate it entirely by opening the GAV and making the mixture a little richer, so I am convinced of the "after-burner" effect going on in the muffler. Yours may be the same, but with a better muffler than I have.

Try opening the GAV. Normal operation is less than a turn counter-closkwise, but try it with it open more.
I agree, a small leak in the exhaust system is a likely reason.
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Old 10-12-2017, 09:25 AM   #6
Big hammer
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Default Re: 31 Roadster "chuffs" when shifting after it is warmed up

Puzzlement?? This same thread had several replies yesterday, then the replies disappeared!
Anyway, exhaust leak at the manifold head pipe connection will make that sound, maybe your muffler is partially clogged with a mouse house!
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