Backfire and stop running

[Al 29Tudor]

A club members model A will start right up but then it backfires and stops running. He has set the timing and changed the condenser and has ordered another coil but doesn't have it yet. He has installed an aluminum intake manifold with new gaskets. Can this be caused by a leaky intake manifold?
Thank for your suggestions, Al

[Ernie Vitucci]

Good Afternoon...He might want to check the little wire between the lower and upper plate on the distributor...Ernie in Arizona

[jb-ob]

While he waits for new parts good time for 6 volt 'tight & bright' maintenance on all wiring connections.

[Chuck Sea/Tac]

Originally Posted by Ernie Vitucci

Good Afternoon...He might want to check the little wire between the lower and upper plate on the distributor...Ernie in Arizona

Especially if it happens when he moves the timing lever!

[nkaminar]

Backfiring can be caused by a number of things. If it happens in the intake then it is usually caused by a lean mixture. If it happens in the exhaust then ignition problems can be the cause.

Besides going through the ignition system, check the fuel flow to the carburetor and check for clogged jets in the carburetor or a clogged float valve. Taking the bolt off the bottom of the carburetor can check the fuel flow from the tank all the way through the carburetor. Do this outside with a fire extinguisher handy.

[Wick]

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If he has a ignition wire instead of a pop-out, the advance rod is probably rubbing/moving the wire grounding it out. Also with the engine running in a dark area, move things around and look for sparks.

[Al 29Tudor]

Thank you all for your suggestions. We are having a tech day today and we'll start off with your suggestions.
Al

[47topless]

My monies' on nkaminar, and his lack of fuel flow theory. A while back, I was having the same symptoms, and he suggested a "lean" mixture was the problem. Mine was due to a crap filled gas tank that resulted in a clogged fuel flow filter valve that severely restricted gas getting down to the carb. It would start, backfire and quit.
rkaminar also gave me a wonderful tutorial on the function of the GAV. Priceless!
Good luck with yours.

[1crosscut]

Originally Posted by Al 29Tudor

A club members model A will start right up but then it backfires and stops running. He has set the timing and changed the condenser and has ordered another coil but doesn't have it yet. He has installed an aluminum intake manifold with new gaskets. Can this be caused by a leaky intake manifold?
Thank for your suggestions, Al

Is this a problem that started after the aluminum intake manifold was installed?

[Gwill65074]

Hi, my 28 Leatherback has just started backfiring through the exhaust after runing great, here is a rundown I have tried to fix the 28,
1. drained and refilled the gas tank in case of bad fuel.
2. distributer points not grounded
3. distributor housing grounde4.
4. points set correctly
5. checked timing.
6. new intake and exhaust gasket and glands
7. manifolds torqued to 40 lbs
8. tried 2 additional carbs
9. compression tests;
dry wet
cyl 1 54 60
cyl 2 53 60
cyl 3 54 60
cyl 4 60 60

with all this it still backfires, if I advance the spark it quiets down

[ronn]

sticky valve?


add MMO to your gas

[Will N]

Another cause of leaning out that can cause backfires and stalling is a clogged vent in the gas tank cap. A bad vent causes a partial vacuum in the gas tank as the fuel flows to the carb, which causes the flow to slow or stop.

[Mulletwagon]

Might also check the valve lash.

[Gwill65074]

Thanks guys, I'll try anything at this point

[ThosD]

Are bushings around throttle plate shaft worn? Are needle valve seats in carb in good shape? Basically; does your carburetor need rebuilding?

[Gwill65074]

I have 3 carbs I rebuilt with new everything and I've tried all 3. Thank you.

[katy]

Originally Posted by Gwill65074

2. distributer points not grounded

if I advance the spark it quiets down

One side of points needs a good ground through the distributor.
It sounde like your problem is in the distributor

[Gwill65074]

That's what i'm thinking, but everything checks out with the distributers. I have 3 and none seem to correct the problem. Right now I'm completely stumped.

[Fullraceflathead]

I wonder if you have internal cross-fire in the distributor cap???

[katy]

Originally Posted by Gwill65074

That's what i'm thinking, but everything checks out with the distributers. I have 3 and none seem to correct the problem. Right now I'm completely stumped.

Check all electrical connections between distributor and coil and between coil and power source. Also possible ignition switch problem.

Is there a vacuum port on the intake manifold? Possible vacuum leak?