Backfire on deceleration

[29spcoupe]

Lately, when I take the Coupe out for a spin, I get backfire on deceleration. It will backfire if I turn the key off too soon. If I let it idle a little before turning the key off, it does not backfire. Thinking that I might be a little rich, I lean it out-no change. Tried to richen the mixture- no change. Checked the points, they are correct. What could be the reason for this. It has only done this for the last couple of outings.

[Chris in CT]

Hi 29,

You are running too lean. You may need to clean out your main and/or cap jets. Happy Motoring!

[Jon]

Check your exhaust gasket.

[Dave in MN]

I had a car backfiring that I spent a whole day trying to stop and it turned out to be a pin hole in the bottom of the muffler. Same symptoms as you describe...When enough air entered the muffler through this little hole to create the correct combustion mixture it would explode. I installed a new muffler and the backfiring stopped. There are other causes and I expect others to add to them shortly but this one is not often mentioned. Hope you solve the problem quickly.
Good Day!

[Tom Wesenberg]

Try turning the fuel off about 30 seconds before you turn off the key. I turn my fuel off at the entrance to my driveway, then when I get in the garage the carb is quite low.

My original Cub Cadet used to let out a shotgun blast about 5 seconds after the engine stopped. It did this for years, then all of a sudden quit doing it a couple years ago.

[George Miller]

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Originally Posted by 29spcoupe

Lately, when I take the Coupe out for a spin, I get backfire on deceleration. It will backfire if I turn the key off too soon. If I let it idle a little before turning the key off, it does not backfire. Thinking that I might be a little rich, I lean it out-no change. Tried to richen the mixture- no change. Checked the points, they are correct. What could be the reason for this. It has only done this for the last couple of outings.

Vacuum leak. It is to lean a mixture.

[Brianfrench65]

Happened to me, turns out it was a bad condenser. Measured 2.4 microfarad. I changed the condenser, and I am all set now.

[emf]

I think we are mis-reading the original post. He said HE backfires on deceleration. Quite a different problem to solve...

Just sayin..

Frank

[29spcoupe]

Other than the suggestion from EMF, who just happens to be my brother, I will check all these things, one at a time and will get back to you. Thanks

[Lycoming-8]

When using my '29 b-coupe as a daily driver a number of years ago, it would backfire quite often when decelerating or even coasting downhill at a steady speed. Years later I realized that it had been running lean and should have opened the enrichener knob a bit. Oh well, it gave my Dad a good laugh when he rode to work with me.

[100IH]

Also, air leaks into the exhaust stream at the flanged connection of the exhaust downpipe of the muffler that connects to the manifold. The flanges frequently need to be reworked and made wider for a better seal.

[BILL WILLIAMSON]

On full throttle, Chief would turn the key off for a couple of seconds, turn it back on & KABOOOOM !----Momma would get FURIOUS!!!
He also had as many HORNS as he could stuff under the hood.
Bill W.

[burner31]

I've been getting some backfiring myself, I will be checking into all these great "simple" fixes.
Some of these causes of back firing I've never heard of before...and would never have thought of myself.

[DJ S]

Originally Posted by burner31

I've been getting some backfiring myself, I will be checking into all these great "simple" fixes.
Some of these causes of back firing I've never heard of before...and would never have thought of myself.

Definitely check for exhaust leaks at the muffler, at the manifold, and at the flange. My Tudor would backfire going down hills and at deceleration but after I had my manifold planed and fixed the leak at the flange, all backfiring has stopped.

[burner31]

I blew out my exhaust manifold gasket back in the summer, I checked it for flatness with a straight edge and it looked good, I should take it and have it milled flat, may do my head this winter also.

[29spcoupe]

Originally Posted by 29spcoupe

I will check all these things, one at a time and will get back to you. Thanks

I turned the GAV richer and the backfire on deceleration is gone. Thanks guys. John

[uk woodie]

enricher knob, where or what is that please

[Y-Blockhead]

Originally Posted by 29spcoupe

I turned the GAV richer and the backfire on deceleration is gone. Thanks guys. John

Originally Posted by uk woodie

enricher knob, where or what is that please

The GAV (enricher knob) is on the lower right under the tank, same knob as the choke. You turn it CCW to enrichen.

If I have my GAV turned in too far I get a little Furt when letting off to shift gears

[700rpm]

Originally Posted by Y-Blockhead

The GAV (enricher knob) is on the lower right under the tank, same knob as the choke. You turn it CCW to enrichen.

Is that the location on RH drive cars as well?

[Y-Blockhead]

Originally Posted by 700rpm

Is that the location on RH drive cars as well?

Good question, I don't know. Carb is on the same side...