Totally stumped. M38 won't start

[qualityhardware]

M38 was running great last weekend and I have about 40 hours on the engine since rebuild.

This week, I started it up, it ran rough and felt like it was firing on one cylinder. It finally stalled out and has not started since.

If I pump the gas pedal or shoot a little ether in the carb, one of the cylinders will fire, but it won't turn over.

I pulled the spark plugs and observed spark on only one of the plugs.

Pulled the cap off the distributor, had a helper crank the engine and observed the breaker points. There was weak spark. I doubled-checked the gap at the points and reset it at .020".

Still weak spark. Checked the coil, it was good. Dropped in a fresh Auto-Lite coil as a test and had the same weak spark.

I replaced the breaker point condenser and got a much better spark.

Put the distributor cap back on and observed good spark on all four plugs.

Screwed the plugs back in and had the same result. Won't turn over, but a shot of ether and/or some gas would get fire in one cylinder, maybe two.

Checked compression (with throttle at wide open) and got the following readings:

1: 110psi
2: 105psi
3: 105psi
4: 110psi

My engine had the cylinders bored at at .060 over when rebuilt because it had already been bored out .030 over in its previous life, so I don't know if the lower compression readings are a function of a wider cylinder / piston combo, but they are still above the 100psi minimum compression allowed for the engine.

I am running a Solex carburetor and have not had any issues with it previously. (Have a Carter YS 637 S that I am rebuilding and will replace the Solex with soon).

I double checked the timing of the distributor and everything lined up correctly at 5 degrees off of TDC, breaking points included.

This Jeep was running flawlessly a week ago, and I just am not getting why this is happening.

[wesk]

Sounds like your ignition is now fine. All that backfiring may have damaged the carb. I wouldn't think those compression figures are the culprit either. Your next stop is the fuel system troubleshooting chart.

1-Is the carb bowl full of gas? (open and look)
2-If it is then do you have full fuel flow from the carb inlet line when cranking the engine?
3-If yes substitute a known good carb.
4-If no then disconnect the fuel inlet line at the pump. Connect a hose to a spare gas can with gas. Repeat #2. Do you have full flow now?
5-If yes then blow back thru line to tank with cap off and verify you can here air flow in the tank.
6-If 5 is yes find the tank vent and suck on it to determine if it is plugged up.
7-If #4 is No then remove the fuel pump, check drive cam to ensure it has been worn down. If cam is ok rebuild or replace the pump.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

[qualityhardware]

OK. Here's where I am.

Pulled the Solex carb off the manifold. There is a puddle of fuel sitting in the bottom of the manifold, right underneath where the carburetor was. Fuel bowl was plenty full as well.

Cranked the engine and observed good fuel flow from the fuel line that feeds the carburetor.

I am rebuilding the Carter YS carburetor right now and will install to see if it makes a difference.

[TomM]

How old is the fuel in your fuel tank?
You are on track with the troubleshooting and thanks for taking the time to spell that out.

I am curious why you have the puddle of fuel in the intake. Do you think its only from the pumping/flooding while you were trying to start or do you think the float needle valve is stuck open?

The reason I asked about the fuel age is that I had a problem with fuel more than 3 months old going bad and causing the needle in my GPW carb to stick. Startup was similar in that it felt like only one cylinder was firing. Upon inspection there was fuel spewing from every carb orifice. A quick cleanout solved the problem.

Let us know how it goes with the carb rebuild.

Tom

[DJ]

I had a very similar problem on my M38. Engine ran fine ,let it set for a week or so and it only fired on one cylinder. Tried everthing a you did,including swapping carbs on my other one. The carb worked fine .Then I remembered I had the same problem on myChevy pickup.It had set about two weeks and then wouldn't start,tried everything and no go. What I did in both cases ,was changed the plugs and as soon as the cylinders cleared up they ran fine. Traced the problem to _uick-_rip gas. Several people in the area have experinced fuel related problems using yhe same gas. So,my suggestion is try different plugs,it worked for me ,twice !! And be careful whose gas you use.

DJ

[qualityhardware]

ARGH.

I swapped the Solex for a Carter YS 637 S that I spent the day rebuilding. Used a kit from Midwest Mil and replaced every small part, valve, etc. after a very thorough cleaning of the disassembled carburetor.

Set the idle mixture screw one full turn backed out from closed.

With the new carb, I am having the exact issue.

Cranking with fully closed choke yields nothing. Not even the fire in the one or two cylinders.

Open the choke all the way and I get some fire in the one cylinder.

Added a little ether to the mix, same issue.

If I open the throttle mixture screw, the single cylinder fires faster or I am getting fire from two cylinders, but it won't turn over and keep running.

I removed the air filter and hose to the crossover pipe so I can see into the carb.

After cranking for 30 seconds with no results, the was a puddle of fuel in the crossover pipe from the fuel bowl vent line coming out of the carb into the crossover pipe.

I quit after that due to the fire hazard of fuel puddles appearing where they shouldn't.

Fuel is about three / four months old, but had Sta-Bil fuel stabilizer in it.

I am totally stumped now. Totally.

[DJ]

Try different plugs,I had the same problem,I had an old army/retired self employed mechanic help me ,we did everything including adjust valves and even an electric fuel pump. We were amazed,diferent plugs and it fired imediatly

DJ

[DJ]

Where are you? 12 or 24 volt military plugs? If Military I would send a set of used ones to try if you want .

[qualityhardware]

DJ,

Thanks for the offer. I ordered some fresh 24v plugs today.

My belief in Occam's Razor tells me your recommendation may be the key.

[wesk]

When you described excellant spark at each plug I assumed they were tested. Plugs will often spark at outside ambient air pressure but not under the higher pressures in the cylinder. That is why we have spark plug test sets that allow us to apply air pressure in a closed chamber to the spark plug tip and see how well it sparks. This is usually caused by allowing the gap to get too wide or as the plug ages with the heat cold cycles the internal resistance grows. Did you check the plugs for the correct gap? Not many shops use plug cleaners and testers any more. We use them religeously in the aircraft repair business where we normally clean and regap and test plugs every 100 hours of ops. If you can't find a auto shop nearby who can test them for you go to your local airport and ask their shop manager to take a look. We use the same type shielded plugs on aircraft piston engines.
_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

[qualityhardware]

Bummer.

Just dropped a fresh set of Auto-Lite 2243s into the engine and zippo. Same problem. I get fire on one cylinder when I crank and nothing anywhere else.

If I close the choke, I get no fire. If it's wide open, I get fire in one cylinder.

If I open the idle mixture screw, the RPM increase a little.

When I pump the gas, the RPM increase a little. But not enough to get it running without the starter.

However, fuel pools up in the crossover pipe because the fuel bowl is getting overfilled and the fuel goes through the vent line into the crossover pipe.

This is so odd. Literally is a case of running great on day A and pooping out on day B with no modifications made in between.

[Jim]

This is just a way-out possibility: could there be a shop
rag stuck in the manifold?

Jim in Darkest Arkansas

[wesk]

Let's see:
Ignition = A-Checked inner cap inner surface for evidence of carbon
tracking or cracks.
B-Checked distributor shaft for excessive play
C-checked point gap and condenser.
D-checked radio noise filter for short to ground.
E-Checked timing.
Fuel = Checked good supply and pressure.
Air = A-Checked and no vacuum leaks.
B-Checked and induction manifold and ducting is unobstructed. Carb
has correct size gasket at manifold. "V" shaped carb base spacer
is installed.
C-Exhaust system is clear and unobstructed. (Can only be verified
by disconnecting head pipe from muffler lead-in pipe.)( not
uncommon for the repop mufller baffles to seperate and block
exhaust flow)
Valves = A-checked cam timing. Has it jumped?
B-confirmed valve lift on each valve.

The small puddle of fuel in the intake is not uncommon when the engine fails to start. It would be less noticeable i the flow divider carb spacer was being used.


_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

[qualityhardware]

Think I found the culprit.

Went back into the distributor to check the rotor. Wouldn't you know it was in two pieces, with a chunk of Bakelite from the flat side reinforcing the spring steel broken off.

Must have been a hairline crack in it that I missed initially.

Ordered two more rotors and will update with results.

[qualityhardware]

Update. Rotor not the culprit.

Distributor cap was toast. Lots o' carbon on that thing. Can't believe I missed it.

New cap. First crank and "viola!" fired right up.

Now there is screaming coming from the bellhousing. Popped the shifter panel and bellhousing panel and it looks like my throwout bearing carrier is out of whack. Funky scoring on the pressure plate where the throwout bearing touches it.

Sheesh.

At least it's running again.