Motor shuts down

[Lenny Bruce]

Hello everyone! My question today is…What would cause my Model A to shut down for a second or two and then fire back up and backfire? I’ve checked the gas flow to the carburetor and it seems nice and strong. The car seems to be under powered at times and then out of the blue it will cut out and then reignite
And Boom!!! Can it be a stuck valve? Any input would be greatly appreciated.
1930 Sport coupe. Thank you

[MilwaukeeMike]

Is your timing set correctly? Some form of vapor-lock?

[Bob C]

Point gap closing up?

[Gary WA]

Originally Posted by Lenny Bruce

Hello everyone! My question today is…What would cause my Model A to shut down for a second or two and then fire back up and backfire? I’ve checked the gas flow to the carburetor and it seems nice and strong. The car seems to be under powered at times and then out of the blue it will cut out and then reignite
And Boom!!! Can it be a stuck valve? Any input would be greatly appreciated.
1930 Sport coupe. Thank you

Valves or air leak manifold!

[Big hammer]

Intermittent ignition switch, does it turn on and off with a snap or sloppy is bad
Mine was intermittent when I first got it, soon after I needed a muffler, working the switch helped mine

[ronn]

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And Boom!!! Can it be a stuck valve?


yes it can be.


In that case, add some Marvel Mystery oil to your gas and run it run it run it.


we too often let our cars sit and then many diff things can happen.

[Ray64]

Wire in the distributer under point plate shorting out, bad condenser, bad coil just to name a few.

[Rob Doe]

Is the boom coming from the carb or the tail pipe? Sticking float? Boom from the carb is lean, (air leak), tail pipe is rich, (likely some black smoke).

Watch the ammeter, if it flickers, likely its in the primary ignition circuit. As said above, low quality point sets cam followers will wear quickly and allow a short to the cam from the point arm. When our coupe did this, it was a 'stumble' or 'buck', but we had no backfire / after fire.

Our coupe recently set for 90 days while I worked on the drive train. After, when I first attempted to start the car, it would not fire off and run. I quickly ran sandpaper through the points, expecting it to take off. Nope. A closer look, revealed a burned and pitted point set, WOW! I had to use a magnifier to get a good look. A new points set and condenser resolved the issue.

[Bob Bidonde]

My guess is you have an intermittent ignition caused by a short circuit, a loose terminal connection, faulty ignition switch, or ????????????
Look for the easy things first. Good luck!

[ArtimusGordon]

Your condenser MIGHT be going BAD. Also check the POINT GAP!

[Lenny Bruce]

I replaced the original type points and condenser with modern style. I will surely make a checklist of all the things mentioned in your responses.. The backfire comes out of the tail pipe. Thanks everyone!!

[BillCNC]

Mine did that at it was the ignition armored cable. The insulation inside the cable became old and dry and was breaking off in three different places. The wire inside was shorting out to the outer cable. I replaced the armored cable and all was good. I left the cable clamp off of the cable since I had no intention of wanting to break a seal on the head just to remove the distributor.

Regards
Bill

[Lenny Bruce]

Good to know Bill thank you I will check that as well!

[Smokedtires]

Ignition coil can short out when hot, not sure if there is a way to test it.

[nkaminar]

The unburnt gas/air in the muffler will ignite causing the boom.

To test to see if the the coil is failing when hot, use the cool spray that is used in the electronic field to test for heat related component failure, or ice.

As the other responses have said, it is likely an intermittent connection or short somewhere in the ignition system.

[Rob Doe]

Lenny, now that you have the modern upper plate, you can temporarily bypass the switch, the heavy cable and the infamous black wire from the bottom plate. Unhook the coil to switch wire and tape the end, run a jumper from the coil to the top plate direct via the spark adjustment opening. Tape the end of the wire from the lower plate, too. Tie wrap the jumper wire to the spark arm of the upper plate. Use your pos + ground cable at the battery, the safety fuse or the fuel shutoff to kill the engine.

[Lenny Bruce]

Wow thank you all so much! Getting all this much appreciated advice really helps motivate
And boost confidence in finding the problem. I love learning more and more about these fun little cars!

[1crosscut]

See if you can borrow a known good distributor from someone else and run that for a while to see if the problem goes away. Will narrow things down a bit.

[Mulletwagon]

Had a similar problem on a boat. Turned out to be a bad wire connection that lost continuity when the connection warmed up. Try shaking all the connections while the engine is running. Good Luck.

[Roxo]

I just had a similar problem yesterday. My truck would miss here and there. I notice the engine stumble at times, then suddenly die. Turns out my wire connectors to the ignition switch would short out to the gas tank. I bent them down a bit and taped them up. Problem solved.