M43 will not restart

[Lucky Bud]

Old guy new to steel soldiers.
have 2 m43’s that will not restart after 10 minutes of idle time.
Both have new rebuilt carbs. New wiring, brand new coils with less than 15 min. On them. Electronic ignition. New vent lines and proper fittings to the intake and to the coil. Idle great. Run great. Lots of power.just will not restart after 10 min of run time. Both have electric fuel pumps.
has to be electrical. Both have spark when trying to restart.
getting ready to shoot em both.
got some ideas?

 

[CMPPhil]

Hi Bud

Have you checked the fuel system for air leaks on the suction side? Also are you sure the tank is venting air into tank?

Cheers Phil

 

[NDT]

Does not sound like classic M37 vapor lock but check that anyway. Make sure fuel line is routed away from exhaust manifold. These trucks will do this but typically after a long hot run. Next culprit might be Chinese coil. If it's chrome it's crap.

 

[cucvmule]

Are you shutting down or is truck dying after 10 minutes? Will it start multiple times while cold?

 

[cucvmule]

I believe like NDT that the coil's are defective. Sounds just like what a coil will do, get hot may, will run while engine is on but after shutdown, heatsoak engine will not start till cools down. But what are the chances that both coils are bad?

If you have one of the old coils put on one of the trucks and see what happens.

CMPPhil and NDT also mention vapor lock as a possible culprit. Do you have the original fuel cap?
If so there is a vent and close setting, for fording.

 

[cucvmule]

M37 Forum Pg3

"Help I am burning up coils in my m43"

Read complete post hope it helps, I had same problem in a Jeep years ago. A lot of the information in the thread still applies even today.

 

[Valley Rock]

Electronic ignition, like, Pertronix ?

If yes, are you still using the ballast resistors or resistor wire in the feed to the ignition coil or the distributor ?

If so remove them, run straight feeds .

 

[Lucky Bud]

Routed fuel well away for fear of vapor lock.
cannot find any coils that are not chrome.

 

[Lucky Bud]

Vented the tank to the atmosphere with no change

 

[Lucky Bud]

Am shutting down and restarting.
it will start multiple times when cold. Never after 10 min.

 

[Lucky Bud]

Routed fuel well away from heat.
and vented fuel.
thanks

 

[Lucky Bud]

All new wiring with no ballast

 

[NDT]

Maybe flooding engine after shutdown due to too much fuel pressure or float level too high spilling raw gas into intake?

 

[CMPPhil]

Hi

A picture of the distributor and coil would help people understand the problem. I suspect you and the rest of us now know that the problem is the coils being heat sensitive. Now to prove that is the problem so you can get on to the solution.

Might suggest the following, start the engine run just long enough to know it runs, 30 seconds, then heat the coil to do this I would suggest a hair dryer. Yes a hair drier like a ProMax, unlike a normal heat gun, hair dryers have a reasonable heat limiter. Set up the hair dyer to heat the coil for 20-30 minutes then try and start the engine.

Just in passing I use a hair dryer for softening rubber connection sleeves to pull them apart, softening old under coat, etc. To make it easier to use zip tie to mount it to one of those welding triangles.

Please let us know what you find. Bad new parts, is not an uncommon or new problem.

Cheers Phil

 

[Valley Rock]

Maybe go to any parts store, or a friendly neighbors back 40 and get a regular old stock coil for a 60s 70s Ford pickup or whatever and put it on and see if problem persists, that would also answer coil heat soak question ...

 

[cucvmule]

NDT has brought up a flooding issue, when some electric fuel pumps are used and the pump puts out more than 7 lbs a fuel regulator is needed to keep the needle and seat from being over loaded, raising float level causing fuel spillover into carburetor.

Just a possible cause, you can also lower float level.

 

[just me]

If you have spark while trying to restart it isn't electrical.
Spark, fuel compression. Something isn't right.
Sounds like heat soak and flood.
Put a REAL pressure regulator on the fuel line ahead of the carb. That little round thing everyone sells ISN'T a good choice.
Holley makes a 3lb adjustable true regulator that works well for about $30.
Next time it dies, crack open the gas cap.
Push the throttle to the floor and leave it there. Do not pump it.
Switch on the ign
Crank it.
If it catches after a few seconds and pukes black smoke while being rough, it has flooded.
Also, make sure the heat riser is set to summer.

 

[Lucky Bud]

Thanks for the input.
One m43 is working. Replaced the new chrome coil and had good results.
working on the other. Good thing I’m retired.

 

[Saberr]

New chrome coils are trash. Went through six of them in less than a year when i restored my m38a1. Any little variance in heat or voltage breaks them. If you have to use them, suggest always keep two spares around per vehicle.