She belches!

[Nlbloch]

How embarrassing! I finally solved my overheating problem (replaced radiator) and took the car out for a test run. But now I notice that every time I take my foot off the accelerator, the car "belches" or "burps." It is almost like a backfire, but not nearly as loud. It appears to come from somewhere under the driver's seat or father back.

Properly timed, choke closed, engine warmed up. Spark retard at proper driving location.

Any ideas on what to investigate?

[Gunmetal blue2]

When you changed the radiator did you get all the air out of the block.

[Nlbloch]

I didn't do anything special to remove the air. What would be the technique?

[darrylkmc]

Nlbloch,

As long as you do not have a thermostat involved, there should be no air in the cooling system once you fill the radiator.

Maybe you can try retarding the timing a bit and/or adjust your GAV.

When it is Belching, I assume it is not belching smoke or coolant or fire or anything.

Darryl in Fairbanks

[tbirdtbird]

open the GAV a quarter turn more.
seriously doubt air in cooling system at this point

[Tom Wesenberg]

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By "belches" do you mean a very light backfire from the exhaust? My car will sometimes do that when I slow down with my foot off the gas.

Where is the spark lever set when this happens? With the stock head, the spark lever shouldn't be less than about half way down after the engine starts. I set my spark about half to two thirds of the way down for most all my driving. Once on the open road I have the spark about 3/4 of the way down, but never all the way down.

If you have a higher compression head, then you need less spark advance. Just make sure the spark isn't too advanced and causing knocking in the engine.

[Nlbloch]

No smoke, just a sound loud enough to hear easily but not as bad as a backfire.

Tom, when you say "half way down" I assume you mean somewhere between 10 and 11 o'clock. My spark advance does not move farther down than just below 9 o'clock, and I thought that was "normal." I have been driving in town (30 mph) with the spark all the way down; perhaps that is part of the problem here altho I never had this problem before when driving with the spark advance in that position. I will try a few different adjustments to see if I can make the problem disappear.

[Tom Wesenberg]

When the timing is set correctly, the lever should move the timing from 0* to 40* BTDC on the crankshaft. The Model A with a stock head does well with about 30*, so I don't move my lever more than about 3/4 of it's travel. Much or my around town driving is with the lever about 2/3 of it's travel. I have a stock head, but with a high compression head I would use a bit less advance.

[P.S.]

Sounds like you may have an intake/exhaust manifold leak.

[Mitch//pa]

agree with tbird open the gav little more or tell us a little more about where you have the spark lever at
you dont have air in the cooling system even with a stat they have a bleed hole.

[Russell in Tulsa]

Originally Posted by Nlbloch

No smoke, just a sound loud enough to hear easily but not as bad as a backfire.

Tom, when you say "half way down" I assume you mean somewhere between 10 and 11 o'clock. My spark advance does not move farther down than just below 9 o'clock, and I thought that was "normal." I have been driving in town (30 mph) with the spark all the way down; perhaps that is part of the problem here altho I never had this problem before when driving with the spark advance in that position. I will try a few different adjustments to see if I can make the problem disappear.

You need to check the window on the dizzy, fully retard and then totally advance and see if the plate touches both edges of the window. If not loosen the clamp on the steering column and rotate until it is correct.

[Nlbloch]

Quarter turn on GAV seems to have done the trick. THANKS!

[darrylkmc]

Originally Posted by Nlbloch

Quarter turn on GAV seems to have done the trick. THANKS!

Good to hear, glad that you posted an update, and that sounded like a reasonable solution

Darryl in Fairbanks