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FLEETVDO 04-09-2020 09:03 AM

1930 82b

Restoration done! It is running and runs very well!

I need a little help please.

I have a little backfire when I accelerate hard and let off the gas to shift.

I have played with the points twenty times.
Gas is good.
GAV out 3/4.
Intake and exhaust re-torqued.
Changed plugs.
I do have an air cleaner on the carburetor.

Any ideas or is it normal?


wmws 04-09-2020 09:31 AM

Re: 1930 82b

How do your plugs look. If rich you might try closing your GAV and see if that helps.

FLEETVDO 04-09-2020 09:37 AM

Re: 1930 82b

Thank for your reply.

I am running with the GAV 3/4 turn open, less and it will stall out and runs very rough.

Plugs are a little soot but changed them again.

Joe K 04-09-2020 09:38 AM

Re: 1930 82b

GAV at 3/4 is a little rich. I run 1/4 turn open. Maybe try no more than half?

Repop jets for the carb are MOST misleading.

The literature has information of carburetor jet sizes and their effect on GAV. See for Vince Falter's take on jet variations. Also scan down that page for more info on Zenith Carbs than you can absorb at one sitting.

Vince Falter has words on advance too. The Model A has about 2x the normal required advance capability. Might have been made this way to accommodate varying skill levels in Timing.


The Model A ignition uses a zero crankshaft degree (TDC) initial timing point so that the engine can be easily started by hand crank, however it should never be run under load in this "retarded" position. The advance lever should always be advanced 1/3 to 1/2 travel (13 to 20 crankshaft degrees BTDC) on the steering column quadrant after starting the engine, and should generally not be run more than 3/4 advanced on the column under any normal circumstances.
More discussion on that page comparing the Model B timing with Model A timing ranges.

Joe K

FLEETVDO 04-09-2020 09:40 AM

Re: 1930 82b

So advance the timing??

30 Closed Cab PU 04-09-2020 09:59 AM

Re: 1930 82b

Is it a backfire in the exhaust as loud as a shotgun, or just a little popping sound which is usually made by the carb?

I had a little popping sound when full deceleration and when shifting. Was running too lean on the Gav, opened the gav up at lower speeds (shifting) and when slowing down from higher speeds about another 1/3 turn counterclockwise on the GAV.

I had a loud backfire when I got my truck back from a Model A shop when turning off the motor. The idle mixture adjust screw was set way too rich.

wmws 04-09-2020 10:05 AM

Re: 1930 82b

Do you know where your timing is set now. Have you checked it with a timing light. There are a million threads here about setting timing.

Jim/GA 04-09-2020 10:09 AM

Re: 1930 82b

Take the air filter off until you figure things out.

Backfire out exhaust pipe is from unburnt fuel. You are running too rich or your spark is weak or irregular (cutting off and on).

Most reproduction carb jets that I have seen are too big, result in running with the GAV closed, not open extra. If your engine runs rough with GAV less than 3/4 open, you have another problem. That rich mixture is compensating.

Is car 12 volts or 6 volts? Positive or negative ground?

What kind of coil are you using? Does the coil have + and - markings next to the posts?

Did you wire everything related to ignition exactly as Ford originally wired a Model A? Pop-out switch? Modern or original style points and condenser?

How have you connected the lower plate inside the distributor to the upper plate? Wire? "Improved" wireless contact?

Have you done a compression test on each cylinder? Please post 3 numbers for each cylinder and they build up when cranking with starter, on warm engine if you can.

We can help you figure this out.

Steve Plucker 04-09-2020 10:17 AM

Re: 1930 82b

Try a different carburetor.


FLEETVDO 04-09-2020 10:23 AM

Re: 1930 82b

I have not used a timing light on it.
6 Volts Pos ground
Yes, coil Has + -
Small popping Exhaust
Nu-rex modern upper plate
I didn't do a compression test

Could it be Exhaust to manifold brass Muffler Clamp Exhaust Seal ?

I have ss exhaust and was told I didn't need it? I am just re-thinking this thing out could that be it?

1931 flamingo 04-09-2020 10:50 AM

Re: 1930 82b

SS exhaust won't affect anything. The GAV is made to be played with while driving, find the "sweet" spot. Set the timing, only has to be done once and you DON'T need a timing light. Go back to the orig style points. FWIW
Paul in CT

Dick M 04-09-2020 10:52 AM

Re: 1930 82b

I had the same problem. It turns out the carb was the problem. I had it rebuilt by Bert's in Denver. Problem solved. The jets needed to be replaced as they were the wrong size.....

FLEETVDO 04-09-2020 10:57 AM

Re: 1930 82b

Ok Thanks,

Brand new tillotson carb

I will play with the GAV

I think I will use the Brass Muffler Clamp Exhaust Seal

I will let you know!

30 Closed Cab PU 04-09-2020 11:17 AM

Re: 1930 82b

Welcome to the Barn, The pictures of your truck in your profile show you have a very nice truck. Is there a story/history behind it?

Let me/us know how the muffler clamp seal works out. I have tried a couple of times to get mine to seal, and I think exhaust is making its way into the carb causing a slight intermittent idle issue.

If interested there is a way to add a picture to you avatar.

FLEETVDO 04-09-2020 11:34 AM

Re: 1930 82b

Thank You.

The Truck is in very nice condition. It was a 10 year restoration project with many new parts and alot of polish.

I do have a slight intermittent idle issue.

I didn't think of that exhaust seal until I started listing what I have done on this forum.

I will let you know about the brass o ring/seal and try closing the GAV.

I don't know how to add an avatar.

Thanks for the welcome and the help. I will let you know.

30 Closed Cab PU 04-09-2020 11:45 AM

Re: 1930 82b


Originally Posted by FLEETVDO (Post 1872067)
Thank You.

The Truck is in very nice condition. It was a 10 year restoration project with many new parts and alot of polish.

I do have a slight intermittent idle issue.

I didn't think of that exhaust seal until I started listing what I have done on this forum.

I will let you know about the brass o ring/seal and try closing the GAV.

I don't know how to add an avatar.

Thanks for the welcome and the help. I will let you know.

My idle issue drove me crazy for weeks. Finally used a flexible metal dryer vent hose sealed on the carburetor air inlet, routed it hanging from a radiator support rod towards the front of the engine. Issue went away. Then noticed a very slight soot mark on the manifold/muffler joint. When running you can not hear the leak.

FLEETVDO 04-09-2020 11:56 AM

Re: 1930 82b

I will keep you posted!

ryanheacox 04-09-2020 01:13 PM

Re: 1930 82b

My car will do the exact same thing. I opened the GAV a little and the popping stopped, maybe from 1/4 to 3/8 of a turn. Sounds like a carb issue if you have to have the GAV out 3/4 turn to get decent performance although I'm not sure how a Tillotson does as far as GAV positions.

Purdy Swoft 04-09-2020 01:50 PM

Re: 1930 82b

A vacume leak will create a lean condition that can cause popping and backfire . Pot metal carburetors are known for vacume leaks, usually at the flange where the carburetor mounts to the manifold . Over tightening the bolts at the manifold flange can warp the flange on the carb . I would remove the carb and use a straight edge to check the carb flange for warpage . If the float is set just a little too low it will cause sloshing of gas in the bowl of the carb that can result in flooding and stalling when coming to a quick stop . The sloshing will flood the carb and usually cause the engine to stall . The flooded gas will enter the muffler . After the engine warms the muffler can get red hot , especially if the timing is too retarded . The hot muffler will set off the flooded gas in the muffler and cause an embarising loud backfire. .

40 Deluxe 04-09-2020 02:26 PM

Re: 1930 82b

Generally exhaust backfiring is caused by a lean mixture and retarded timing. First step is to just get everything set to factory specs. When I was in high school a classmate bragged that his friend's Model A would "pop 40 times going down a hill!". The trick to get those backfires was to throw the timing lever all the way up and close the GAV as you let off the gas at the top of the hill.

Remember, ethanol fuel has the effect of leaning the air/fuel ratio so you need to open the GAV some more to compensate if you're running that stuff.

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