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M43 will not restart

Lucky Bud

Member
44
35
18
Location
Kerens Texas
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

Well-known member
535
373
63
Location
Temple, NH
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

Well-known member
Steel Soldiers Supporter
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113
Location
Camp Wood/LC, TX
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

collector of stuff
1,129
552
113
Location
Crystal City Mo
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.
 
Last edited:

cucvmule

collector of stuff
1,129
552
113
Location
Crystal City Mo
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

Big wheeler cat peeler
Steel Soldiers Supporter
313
503
93
Location
Rogue Valley OR
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 .
 

NDT

Well-known member
Steel Soldiers Supporter
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Maybe flooding engine after shutdown due to too much fuel pressure or float level too high spilling raw gas into intake?
 

CMPPhil

Well-known member
535
373
63
Location
Temple, NH
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

Big wheeler cat peeler
Steel Soldiers Supporter
313
503
93
Location
Rogue Valley OR
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

collector of stuff
1,129
552
113
Location
Crystal City Mo
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

Member
322
10
18
Location
phoenix,az
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.
 

Saberr

Active member
185
84
28
Location
Temecula,Ca
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.
 
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