My new project: 1964 USMC M38a1

wilfreeman · Post by **wilfreeman** » Thu Apr 12, 2018 6:28 pm

This morning I stopped at O'Reilly Auto Parts and picked up 8' of 7/32" vacuum line and a couple of 5/16" fuel line fittings (I have extra 5/16" fuel line at home). When I got to the shop, I replaced all of my vacuum hose - only needed about 7' of it. Started the engine and - NOTHING - they didn't even try to move. I sprayed a little WD40 in the air inlets and worked them a little - no change. Oh well, at least it has new hoses now - I guess it needs more vacuum! I looked at my other Jeep and noticed I had put 1/4" hose on it - maybe that's why those wipers don't work so well with all new components? I will be changing those hoses out at a later date.

Next, I made up a new short hard fuel line to go between the fuel shutoff and the flex hose, but I could never could get it to stop leaking where the flex hose threaded on the new short hard line. I am guessing the flex hose threads are messed up - I ran out of patience (and time) with it. It doesn't leak until you stop the engine - pretty sure it is pulling air from there. I will probably go back to the setup I had before I bought the new flex hose (rubber fuel line hose clamped to the short hard line and a nipple in the fuel pump fitting) for the time being. I'll order a hose and install it if it gets here in time.

After I made the new hard line and installed it, I went for a drive - started acting up when it warmed up, so I reached down and took the gas cap off - didn't help, but that was before I knew I still had a gas leak.

Got back to the shop and checked the timing - about 12 BTDC, so I adjusted that to about 7 or 8. Idled like it is missing - adjusting the mixture screw on the carb didn't help and had to adjust the idle screw a LOT to get it to idle.

With that said, I am thinking that my valves are too tight, causing it to start missing as it warms up. I only have about 8-10" vacuum also. This engine is VERY quiet compared to my other one - can hardly hear ANY valve noise! What do you think? This will probably be my first area to check.

Mike_B · Post by **Mike_B** » Thu Apr 12, 2018 8:15 pm

If your fuel leak is after the pump it can't be sucking air as that's the high pressure side, all it can do is leak out...that's not your problem...

Sounds like you need to check valve clearance, you should hear a little ticking as the valves close...

My .02 cents

Mike B

wilfreeman · Post by **wilfreeman** » Thu Apr 12, 2018 8:43 pm

The leak is between the shutoff valve and the flex line - before the pump.

Yeah, check/adjust the valves are the first order of business Saturday morning - not looking forward to pulling the dude valve cover!

mdainsd · Post by **mdainsd** » Fri Apr 13, 2018 8:41 am

8 to 10" of vacuum is not very good.

Both of my M38s and my M37 run 20 to 21"

There should be a little bit of valve noise, I liken it to a nicely oiled and running sewing machine.

wilfreeman · Post by **wilfreeman** » Fri Apr 13, 2018 9:17 am

I knew it wasn't good - figured tight valves might be causing the low vacuum. Mine is as quiet as a new OHC engine. Actually as quiet as all of my vehicles. I'll be pulling the covers to check tomorrow - I just have a feeling.

Mike_B · Post by **Mike_B** » Fri Apr 13, 2018 1:44 pm

Fuel leak before the pump WILL suck air...put Permatex II on the threads to seal then up.

There's a good valve adjusting on YouTube...should be an easy job...once the covers are off!

Mike B

wilfreeman · Post by **wilfreeman** » Sun Apr 15, 2018 8:50 am

Update from yesterday's work on the Jeep.

I adjusted the valves to .016" exhaust and a "loose" .016" intake. Took a test drive and once again, after it warmed up it started missing, running rough and a slow idle that you had to throttle it to keep it running.

While I had the side cover off, I cleaned and painted the cover, bell, fording valve and PCV valve. After the test drive I noticed a fairly loud hiss which turned out to be multiple vacuum leaks. I tightened up the fording valve/PCV valve (which loosened the nipple to tee connection right after the PCV valve). These connections haven't been loosened in MANY years, so you can imagine what a PITA they were to break loose without stripping! I 2 more leaks at the vacuum port elbows (bottom of the pump) - I removed the elbows and added Teflon tape so that I could get them to a point that they were tight and at the angle I needed. This fixed my vacuum leaks, which helped the idle. While I was down there, I removed the flex fuel line (that I couldn't get to stop leaking), installed a nipple on the fuel pump inlet elbow and installed a rubber fuel line and hose clamps - definitely not sucking air there anymore.

I took another drive - same result after it warmed back up.

I was running out of time, so I decided to put the original distributor back in. This one has the breakerless ignition module in it, so I could rule out the condenser. Once installed, I set the air gap with the provided plastic feeler gauge. I installed the distributor adaptor to connect a dwell meter and connected a timing light. I fired it up and adjusted the timing to 5deg BTDC and idle to 700rpm. I adjusted the carb for the smoothest running. The dwell showed 30. Correct me if I'm wrong, but the dwell angle only matters with points, correct? It was showing 38 with the other distributor installed - it is supposed to be around 45 with points, right?

I took another test drive and although it ran better, once it warmed up it started doing the same thing! It runs fine as long as I keep the rpms up, but once you slow down to a crawl it starts surging and wants to cut off.

I am running out of ideas on this Jeep. I didn't try disconnecting the fuel line before the pump to try pulling gas from a gas can to rule out sucking air from the rest of the line. Nor did I try re installing my "redneck" gas tank to gravity feed the carb to rule out fuel pump problems. I checked all of my coils last year, and they show in spec.

Post by **wesk** » Sun Apr 15, 2018 9:23 am

Assuming you are 100% good on coils and air leaks.

Check compressions hot versus cold. You may have a piston fit issue. Or with the engine cold apply tension to the belts and turn the engine over by hand. Then run it till hot and try turning it by hand again.

If you can get your hands on a thermal radiation style heat meter compare head temp at base of carb to head temp at the thermostat and again to block temp. If you have a wide spread in temps with some quite high you may have clogged water passages getting the head too hot.

4x4M38 · Post by **4x4M38** » Sun Apr 15, 2018 1:30 pm

Your heat riser valve is operating correctly, right?

wilfreeman · Post by **wilfreeman** » Sun Apr 15, 2018 8:01 pm

Good idea - I'll check temps when I get off on Friday. I also want to check the air flow across the coil to make sure it's not overheating.

No heat riser on the a1 Brian.

m3a1 · Post by **m3a1** » Sun Apr 15, 2018 8:28 pm

Sounds like it might be getting air into the mixture after the carb from somewhere, creating a lean condition. Have you explored that possibility?

wilfreeman · Post by **wilfreeman** » Mon Apr 16, 2018 9:31 am

The other week I found a MAJOR leak in the carb - manifold gasket. It would hardly run. I replaced the gasket and it runs a LOT better - until it gets hot. I didn't check the carb base while I had it off - I guess I could check that and check the mounting nuts again.

wilfreeman · Post by **wilfreeman** » Fri Apr 20, 2018 2:08 pm

This afternoon I checked all of the vacuum line connections and tightened a few a little. Also made sure the distributor line was clear and had the oriface in the tee end. Then I got the wild idea to check the fuel pressure. I hooked in at the hard line before the filter before the carb (I know it should be checked at the pump, but I don't have a 1/4" barb fitting - figured this would be just as good since it is a hard line). I cranked it over and only got 2 - 2.25# of pressure.

Here's a link to a video of it not running right:

https://youtu.be/UMKJHTWWNrk

Post by **wesk** » Fri Apr 20, 2018 4:13 pm

Does your pump have the spacer between it and your block?

wilfreeman · Post by **wilfreeman** » Fri Apr 20, 2018 4:15 pm

It has the 1/2" spacer on it Wes. I'm leaning toward a worn out fuel pump lobe. I might pull the pump tomorrow to check that.