M38 wont start without starting fluid

ih8pepl · Post by **ih8pepl** » Thu Jul 16, 2020 11:54 am

Ive racked my brain on this for the last week. I need help before I develop an aneurysm.

After a exhaust manifold gasket replacement I took the M38 on a leisurely 10 mile cruise - it did 100%. It would not start the next day.

Cranks, but wont even attempt to fire up. Took the crossover tube off the intake and sprayed a little starting fluid in - started right up - ran great once it burned the starting fluid and drives fine at all RPMs - but shut it off again and you will need starting fluid.

Now it chokes out as soon as the crossover tube is put back on. Fuel/Vacuum pump issue?

Compression is 85-95 psi
I have air, fuel and good spark

Ive gone through the distributor replacing the original 50s era coil and capacitor, new condenser. Wires/plugs are all good. Disassembled and cleaned the carb with a new gaskets and diaphragms. Drained the all the fuel, and put fresh gas back in - no change.

Thoughts? I know its something thats right in front of me, im just not seeing it.

RonD2 · Post by **RonD2** » Fri Jul 17, 2020 7:35 pm

Hello "I Hate People",

We're all waiting for Wes to chime in!

In the meantime, did you put a gauge on your fuel pump and see if the pressure is within spec?

By the way, I'm not people. I'm a Marine

Good luck!

Post by **wesk** » Fri Jul 17, 2020 8:13 pm

I think before I chime in can you explain what is meant by:

Now it chokes out as soon as the crossover tube is put back on.

ih8pepl · Post by **ih8pepl** » Fri Jul 17, 2020 9:00 pm

wesk wrote:I think before I chime in can you explain what is meant by:
Now it chokes out as soon as the crossover tube is put back on.

Like I said, it ran like a top one day. Tried starting it the very next day and nothing.

Curently:

With the engine cold, I remove the small crossover tube between the carb and intake. I spray a little starting fluid into the intake tube. Jeep starts right up, runs a little rough till the starting fluid is gone, then idles a little high with the crossover tube removed. Once the jeep is running, if I attempt to put the crossover tube back, the jeep immediately drops RPMs and the engine stops.

It will also start with starting fluid and the tube in place but wont fire up as easily. Takes a little more cranking.

Without starting fluid, I can crank it till the batteries are dead and I cant even get a hint of ignition.

Fuel pump pressure is just shy of 4psi

Im stumped...

ih8pepl · Post by **ih8pepl** » Fri Jul 17, 2020 9:07 pm

I will mention, that I am still learning as I go, and im not familiar enough with the dual action fuel pump. Im wondering if there is something going on with that that is causing my initial start problem...

Post by **wesk** » Sat Jul 18, 2020 12:20 am

I am hearing two different things here. Could you clarify?

if I attempt to put the crossover tube back, the jeep immediately drops RPMs and the engine stops.

This I understand clearly.

It will also start with starting fluid and the tube in place but wont fire up as easily. Takes a little more cranking.

This only tells me it will start with the tube in place. My question now is does this mean it will run with the tube installed if it is started with the tube installed?

Also is the engine and it's accessories all stock/original?

ih8pepl · Post by **ih8pepl** » Sat Jul 18, 2020 8:47 am

wesk wrote:I am hearing two different things here. Could you clarify?

if I attempt to put the crossover tube back, the jeep immediately drops RPMs and the engine stops.
This I understand clearly.

It will also start with starting fluid and the tube in place but wont fire up as easily. Takes a little more cranking.
This only tells me it will start with the tube in place. My question now is does this mean it will run with the tube installed if it is started with the tube installed?

Also is the engine and it's accessories all stock/original?

It will start with the tube installed after injecting starter fluid in the intake but requires more cranking than normal to get it to fire up and runs at a slightly lower rpm than normal but still idles nicly and runs at all RPMs.

It just will not start without help. And I just finished checking all the lines from the tank to the pump for loose fittings, kinks or bends... all is good.

4x4M38 · Post by **4x4M38** » Sat Jul 18, 2020 8:42 pm

A couple of questions.
Do you have the full factory fording ventilation system installed, and if so, the early system or late?

Did you put all of that back correctly when you put the manifolds and carb back on?

Are your fording valves open?

Post by **wesk** » Sat Jul 18, 2020 11:16 pm

While you answer Brian’s guestion on fording systems would you please answer the question I posed above:

Is your M38’s engine and fuel system completely stock.

ih8pepl · Post by **ih8pepl** » Sun Jul 19, 2020 9:45 am

Everything is mil spec - fording system is installed correctly and valves are open. Late style fording valves.

Fuel system is stock setup. No manual priming handle. I didn't do the restoration on this M38, one thing that I find interesting is that the fuel pump is "Varnished" with a sealer. Which I don't recall seeing done for rebuilds. Ive only seen similar on a Military M38 crate motor. NOS? If it is, I bet those diaphragms are getting spongy from modern gas.

Post by **wesk** » Sun Jul 19, 2020 10:41 am

More likely that is cosmoline. Military used it on everything from crated engines to no’s parts.

Back to your symptoms: the problem you describe

starts with starting fluid then run ok

tells me the fuel delivery to the carb is fine after you get her started. This means your fuel delivery to the carb is fine and pump output is adequate. So let’s not beat that system to death.

If your choke plate is working and the accelerator pump & metering rod diaphragms are working properly then this need for starting fluid is because every time you shut down & sit awhile your carb’s bowl is draining out somewhere and leaving your bowl empty when starting.

Bowls get empty after shutdown 2 ways: 1 - It leaks. 2 - It cooks off the gas or perks is another term after shutdown. This is caused by excessive heat buildup under the carb. Most common reason for this is a heat riser valve in the exhaust manifold is stuck in the heat on position. Go to my photo album and pull up my sub-album “M38 Fuel System”. Then review the tech photos of the heat riser system.

ih8pepl · Post by **ih8pepl** » Sun Jul 19, 2020 11:02 am

wesk wrote:More likely that is cosmoline. Military used it on everything from crated engines to no’s parts.

Back to your symptoms: the problem you describe
starts with starting fluid then run ok
tells me the fuel delivery to the carb is fine after you get her started. This means your fuel delivery to the carb is fine and pump output is adequate. So let’s not beat that system to death.

If your choke plate is working and the accelerator pump & metering rod diaphragms are working properly then this need for starting fluid is because every time you shut down & sit awhile your carb’s bowl is draining out somewhere and leaving your bowl empty when starting.

Bowls get empty after shutdown 2 ways: 1 - It leaks. 2 - It cooks off the gas or perks is another term after shutdown. This is caused by excessive heat buildup under the carb. Most common reason for this is a heat riser valve in the exhaust manifold is stuck in the heat on position. Go to my photo album and pull up my sub-album “M38 Fuel System”. Then review the tech photos of the heat riser system.

Its not cosmoline - its definitely some sort of brushed on varnish

The fuel level in the carb bowl is always about 3/8" or so from the top when I take the horn off. Even after sitting for a day or two. Ive checked the bowl 3 times. 1) cleaned and inspected the carb. 2) to make sure the float/valve were working and adjusted properly. 3) To drain the gas and fill the bowl with new gas. It always has plenty of fuel in the bowl.

The diaphragms I have in the carb are about a year old. I have a NOS carb that im going to try, just waiting on a set of new diaphragms for it. Hopefully that will change something.

The heat riser is working just fine... new spring. Heated it up and it opens/closes just as it should, and isnt slipping or snagging on anything. Just started the jeep with fluid and watched it open up.

Post by **wesk** » Sun Jul 19, 2020 7:37 pm

OK, then fuel availability is also not an issue.

Next we go to correct springs and spring positions in the two diaphragms in the carb and a current check of each diaphragm to insure it is functioning and not damaged or deteriorated.

ih8pepl · Post by **ih8pepl** » Sun Jul 19, 2020 8:36 pm

wesk wrote:OK, then fuel availability is also not an issue.

Next we go to correct springs and spring positions in the two diaphragms in the carb and a current check of each diaphragm to insure it is functioning and partially disolved.

Yep, I have some inbound this week. I appreciate all the suggestions!

Jeff_Lee · Post by **Jeff_Lee** » Wed Jul 22, 2020 8:29 pm

wesk wrote:... it is functioning and partially disolved.

Wes, I am missing something on the "partially disolved" statement. Are you concerned that the diaphragms are desolved by ethanol fuel?