Backfire after the key is shut off

Check your timing first and make sure it's spot on. Print and follow these easy instructions and your car should run correctly if everything else is working properly.

http://www.abarnyard.com/workshop/timing.htm

It may also be vacuum, wiring, rough edges in the combustion chamber, bad muffler, carb adjustments, etc. Make sure your distributor is set up properly first before you go chasing other gremlins.
 
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Elrod said:
Check your timing first and make sure it's spot on. Print and follow these easy instructions and your car should run correctly if everything else is working properly.

http://www.abarnyard.com/workshop/timing.htm

Now, you are about to get 15 other suggestions after mine about vacuum, wiring, rough edges in the combustion chamber, bad muffler, carb adjustments, etc. Make sure your distributor is set up properly first before you go chasing other gremlins.
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ill keep quiet then go with the timing
 
I do apologize if my response sounded rude. I didn't mean it to and I'm going to go back and edit. I was just meaning what Jerry was able to say more eloquently, which was just try the simple things first before moving on to other issues. I was just thinking that sometimes when people are new to the hobby, trying to track down a problem can be confusing. I know it was to me when I got my first Model A!

Mitch is an A.S.E. Certified Master Technician and you have a lot of really seasoned Model A experts with wealths of knowledge and many miles under their belt, so I'm sure you will get some great advice to get that A back up and running like a fine tuned watch!
 
A common cause is too high an idle, and too rich a fuel mixture. It can be fun though, at a gas station.
 
I don't think it's timing, since the ign is off when the phenomenon takes place, and the still-rotating engine can charge the combustion chamber and even the exhaust system with F/A. Rich mixture, incandesent carbon build-up in the combustion chamber and open exh valve when engine stops may go kapow, unless there is enough unspent fuel in the whole exh syst and incandesent carbon in the exh manifold to do the same, or both. I love the various reactions it causes in innocent by standers.
 
Exhaust manifold leak often a cracked manifold. When you turn it off the engine dumps some unburned fuel into the exhaust. As the exhaust cools it draws fresh air in thru the leak until the mixture in the exhaust is right for the hot manifold to ignite it. If you are quick you can get far enough away to pretend it's not your car.
 
Mine did the same thing. I could almost get out of the car before it would happen. Scared the whole family. It was the timing on my car.
 
Elrod said:
Check your timing first and make sure it's spot on. ....
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I'm trying to understand why timing would do it; can you explain? Most likely too advanced or too retarded? Thanks!

Is it simply retarded timing overheating the exhaust system, or unburned fuel from that interval between when the spark should have fired and when the key was turned off being pushed out the exhaust?

Steve
 
My first model A also backfired when shutting off. Quite a number of people are intimidated by the distributor, and run first to idle mixture screws, etc. If the spark is not igniting the air / fuel mixture in it's entirety before the exhaust valve opens, that can cause a build up of explosive gas in the hot tail pipe.

And from experience, my car also did the same thing and once I timed the car properly, the backfire stopped.

You can run the car without an exhaust manifold at all. So a leaky exhaust manifold sounds strange to me. I've had plenty of exhaust leaks, and even driven for an hour with the entire tailpipe removed from the car after it kept falling off on a 300 mile road trip.

So, all I'm saying is before removing and replacing exhaust manifolds, and adjusting valve lash or rebuilding the carburetor, just check the timing, and if it's spot on, THEN start looking at the other more expensive options. These old A's are really simple beasts though, and often the simple answer gets you back on the road. That's why I love 'em!
 
I adjusted the timing, and points as your advice, and it does run a lot better. Seems to have more power. But I am not sure if it is dead on. I havnt had any backfire. It only did it the one time and I may have shut off the key before it had idled down. thanks for the help
 
Back in the olden days when I was 16 and driving my first Model A I took a very cute girl on a date to the local movie theater. When we returned to her driveway and I turned the key off, the Model A backfired really loud and embarrassed us both. Mostly me. I'm going to see her again this fall at our 50th class reunion. As you might guess our relationship went nowhere.
 
In my case it was the float being set too high. Making that adjustment and retarding the spark to its highest position and puttng the throttle in its highest position did the trick for me. Also, by waiting for a few seconds putting the "ears in the up position seems to prevent the backfire.

Jack
 
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