M37 Mystery Problem

[copperline]

One more update and more confusion.

I had pulled all of the plugs early yesterday (around 11am). The plugs sat out overnight as did the engine. No plugs installed.

This morning just in preparation for the new coil coming in, I put all of the plugs back in. I was 100% sure she would start and she did. Started right up, pumped the throttle a bit and kept her running for 3 mins or so, pulled the throttle handle out a bit and let her high idle. I sat here and just watched. She ran for a few more minutes then it started surging and getting worse and popping and eventually shut off.

Tried to start her again and nothing. Just round and round.

I have been restoring cars all my life and this mystery really baffles me.

 

[NDT]

One more update and more confusion.

I had pulled all of the plugs early yesterday (around 11am). The plugs sat out overnight as did the engine. No plugs installed.

This morning just in preparation for the new coil coming in, I put all of the plugs back in. I was 100% sure she would start and she did. Started right up, pumped the throttle a bit and kept her running for 3 mins or so, pulled the throttle handle out a bit and let her high idle. I sat here and just watched. She ran for a few more minutes then it started surging and getting worse and popping and eventually shut off.

Tried to start her again and nothing. Just round and round.

I have been restoring cars all my life and this mystery really baffles me.

that last scenario sounds a lot like stuck carb float needle valve causing a flood.

 

[copperline]

I will certainly check that tomorrow morning.

 

[copperline]

It's not a stuck float. Checked it this morning. Either something is fouling the plugs (not fuel) or the coil just doesnt have the umph (maybe thats fouling the plugs?)

We will know soon enough, coil should be here in a few days.

 

[Floridianson]

that last scenario sounds a lot like stuck carb float needle valve causing a flood.

Or a lean condition will cause popping. Wonder if the is a fuel restriction.

 

[Squirt-Truck]

You did not say that....
Those are good units. Petronix
Are the grounds good?

 

[copperline]

Here is the latest. Brand new coil, new old stock not the chrome imports, new cap and new rotor. Got it all installed, and she started right up. Instantly. Note that the truck has sat for about 5 days without turning over.

Ran exactly like before, few minutes no problems. A little grumbly but running. Shut her off to close the hood and remove the chocks to maybe take her for a drive around the ranch. Got back in and NOTHING. Just turned over and over and over. Not even a cough.

Same as always. Runs a bit then done. It's definitely not ignition, not timing, not ground, not contaminated fuel, not wiring.

My gut is telling me that something is quickly fouling the plugs (wet plugs). Either fuel or oil.

Attached are two pictures of Cyl 2 plug. These plugs are brand new with a total of about 6 minutes of running. The other plugs look the same. Wiped them with a cloth and lots of black oily soot. The plugs do smell like gas but not overpowering gas smell.

I did check the float needle valve and that seems to be working. I disconnected the fuel intake pipe and using a rubber hose tired to blow air into the carb knowing the bowl was full. Couldnt blow any air. Drained the bowl and tried again and was able to blow air. Makes me think its not the needle valve.

So I'm at a total loss. Could i have a blown head gasket and oil is getting into the cylinders?

I have no idea and this is really starting to get frustrating (and expensive).

Any thoughts?

 

[bigdog1949]

Here is the latest. Brand new coil, new old stock not the chrome imports, new cap and new rotor. Got it all installed, and she started right up. Instantly. Note that the truck has sat for about 5 days without turning over.

Ran exactly like before, few minutes no problems. A little grumbly but running. Shut her off to close the hood and remove the chocks to maybe take her for a drive around the ranch. Got back in and NOTHING. Just turned over and over and over. Not even a cough.

Same as always. Runs a bit then done. It's definitely not ignition, not timing, not ground, not contaminated fuel, not wiring.

My gut is telling me that something is quickly fouling the plugs (wet plugs). Either fuel or oil.

Attached are two pictures of Cyl 2 plug. These plugs are brand new with a total of about 6 minutes of running. The other plugs look the same. Wiped them with a cloth and lots of black oily soot. The plugs do smell like gas but not overpowering gas smell.

I did check the float needle valve and that seems to be working. I disconnected the fuel intake pipe and using a rubber hose tired to blow air into the carb knowing the bowl was full. Couldnt blow any air. Drained the bowl and tried again and was able to blow air. Makes me think its not the needle valve.

So I'm at a total loss. Could i have a blown head gasket and oil is getting into the cylinders?

I have no idea and this is really starting to get frustrating (and expensive).

Any thoughts?

Did you try the float level ?

 

[JD4044M]

Sound like your flooding it which will kill a good set of plugs on the first try. Pull the plugs and burn out the cylinders with a match or let it set for a few hours with them out. You can bake the plugs clean with a heat gun and not have a carbon problem. Make sure your float is not stuck in the carb and just dumping fuel in it. Full open choke and make sure your manifold id not all wet too. More than once I have had a M37 go hard start new plugs would fire off then flood out. Very frustrating when it happens. Just saw your plugs and yes your flooding it as long as you have spark too. Glad you got the Rotor Seated right. That plug will not fire off now to fowled and wet. Don't us a wire brush clean them with heat. Till you get all that fuel out of the manifold and head it will keep fouling. Solve the to much fuel problem first.

 

[copperline]

Are there any good guides to checking and adjusting the float level?

 

[JD4044M]

I would have to look it up in a manual to be sure been a while but done by bending the tap over the needle valve. First take the top off the carb this takes 2 people. Lock the float hinge down so the float can work. Disconnect the Coil power plugs out and bump the engine over and watch the level in the bowl normally the float will be level when it shuts off the fuel and 1/8 to 1/4 inch from the top. Check to see if the fuel will stop filling when the bowl is full. Fuel can over fill the bowl and dump down the manifold and cause the flooding. Long as the fuel level is below the top edge and shuts off your pretty much OK. Check for junk in the bowl while your in there, also below the needle seat.

Go here and read these guys know M37s M37 Info

 

[copperline]

Ok here is the labor day update.

Pulled the top of the carb and adjusted the float level. Cleaned out the bowl and cleaned out the jets (no contamination anywhere). Turned the engine over with a camera recording the carb and once the bowl filled up the gas stopped flowing. Seems like that is good. 5/32" is what I set it at. It was a big high.

As recommended I baked the spark plugs to clean them and lit each cylinder with a long lighter. First time I do that! A few of them did make a cool whoosh.

Got the truck all back together and as I fully expected she started right up. Rough idle, fantastic at higher RPM. Ran her for a few minutes then turned her off. Tried to restart and she did (first time on second restart). Ran her a few more minutes then shut her off. 10 minutes or so later, tried again and nothing. Not even the slightest cough. Tried again another 10 minutes later and still nothing. Just turns over and over. I am 100% sure if I pulled the plugs and let it air dry for a day she would start right up again. Something is fouling the plugs (i think).

So right back to the beginning.


Any more ideas?

 

[NDT]

Any time it won't start, remove the plugs, reattach to the wires, crank it and verify you still have a hot blue spark on all 6 plugs.

 

[Squirt-Truck]

Starting to sound like a flooded crankcase.
Check th oil level and for fuel....

 

[copperline]

Here is todays update.

Got in the truck early this morning and she started right up. This is different than before where it would take weeks of sitting there or me pulling the plugs to air the cylinders out. Very rough idle. Didn't need any choke to start. Idle sounds more like a Harley than anything. Really clunky and pulsing. Higher RPM's sound great. Let her run a bit then shut her off. Tried again and she started. Oil pressure very good. Ran her a few more minutes then shut her off. Wouldnt restart the third time. Just round and round.

As suggested I pulled each plug out and checked for spark. Each plug had what seems like a decent spark. Certainly not blue but bright white with maybe a bit orange if anything.

The plugs were dry but had a lot of black dry soot on them. So much that they would leave a steak on a shop towel.

I'm wondering if i have a mixture problem and am running rich? Maybe timing?

Is there any way to adjust the mixture? FYI, the idle screw on the carb does nothing. In or out doesnt change the terrible idle.

Ready for more suggestions as this is getting old quick!!!

 

[John Mc]

Were you adjusting the idle speed screw or the idle mixture screw?

My manual has them correctly identified in one place, but has the identities reversed in another picture.

 

[copperline]

Oh I may have discovered a big problem here. I checked the oil dipstick and it was higher than the high fill line. Several months ago I noticed the same thing and drained the oil. The oil seemed very thin at the time. I put new oil and made sure I was right in between the lines on the dipstick.

Now it's higher again. I'm starting to wonder if i have gas getting into the oil. Maybe the float was bad and flooding the engine.

I just read the fuel in the oil will start to flash when the engine is warmed up causing flooding symptoms.

OR I have a stuck intake valve OR I have a hole in my fuel pump diaphragm.

Oh man this is never ending.

Any thoughts?

 

[GopherHill]

Good thought re: fuel pump diaphram. Don't remember if the military pump has a vent hole in the pump that will weep fuel if you have a ruptured diaphragm. My thought is that the truck needs to get run with the hand throttle set to run some above idle until normal operating temperature - maybe an hour. This is mechanical conditions permitting. Watch the oil pressure and temperature.
Years ago you could get fuel pump rebuild kits, don't know about now.
good luck.

 

[NDT]

Good catch on the oil level. For sure if you have an old crusty diaphragm in your fuel pump, gas will end up in the crankcase. Fix this before doing anything else. The soot on your plugs means overfueling. Stuck valve would be a horrible engine miss.

 

[Squirt-Truck]

Fuel in oil.....
Pump diaphragm.