M38A1 Trouble Starting

Madriver1968 · Post by **Madriver1968** » Sat Sep 28, 2019 4:16 pm

Hi gents,

I am having a devil of a time starting my freshly refurbished M38A1. Over the course of the refurbishment, I've replaced the distributor (replacing a jury-rigged 12 volt distributor installed by the prior owner), the fuel pump and the carburetor. I’ve got a 24 volt system.

I've got fuel at the carb, and spark at each spark plug. When trying to start it, the engine has caught once or twice, but that's it.

Any advice would be most welcome.

Thanks!

bamaj · Post by **bamaj** » Sat Sep 28, 2019 5:38 pm

Sounds like you have the basis covered. The other thing I think of is timing. Spark is necessary but it needs to be at the right time.

zeke57 · Post by **zeke57** » Sat Sep 28, 2019 8:34 pm

I had the same problem trying to get my f134 running. I had spark and fuel and it would fire but not stay running turned out I had a major vacuum leak. After correcting the problem it fired right over and ran good.

Post by **wesk** » Sat Sep 28, 2019 8:57 pm

Have you run the troubleshooting checklist in TM 9-8014?

Sect IV paragraph 80 starting on page 79. If you do not already own this manual you can download a copy in PDF free here on our downloads page.

Shotgun (hit & miss) troubleshooting by responding to one suggestion at a time is a huge waste of time and money. It is best to take a detailed step by step approach while keeping good notes.

jnissen · Post by **jnissen** » Sat Sep 28, 2019 10:39 pm

Use good gas!

Madriver1968 · Post by **Madriver1968** » Sun Sep 29, 2019 9:44 am

Thanks all - I'll start working on the checklist.

In the meantime, since I've installed a new carb, what should the idle screw be adjusted to? I know how to adjust it once it's up and running, but what's a good starting point for a carb when it's first installed?

Thanks again!

Post by **wesk** » Sun Sep 29, 2019 12:23 pm

The general rule is screw it full in gently then back it out 1 1/2 turns for a reasonable starting point.

Madriver1968 · Post by **Madriver1968** » Sun Sep 29, 2019 1:24 pm

Thanks Wes.

Here's where I am. I've located TDC using the method Wes previously outlined on this site. I've adjusted the dizzy so that at TDC, the points are just starting to open. I've confirmed that I have spark at all plugs - 1 and 4 are very bright white, though the spark at 2 and 3 are a tiny bit yellow.

I have tested the fuel pump by removing the fuel line from the carb and cranking the engine, and I'm getting fuel nicely. I checked the plugs again and they were wet, so I turned in the idle screw in a half turn.

I've gone through the check lists identified by Wes above, and to best of my abilities, everything seems ok. I don't have the ability to check fuel line pressure, but as noted above, when I tested it by removing the line from the carb and positioning a jar there, I am getting nice spritzes of fuel out of the line when the engine is cranked.

The engine caught for a second or two, but won't run.

Perhaps the weaker spark at 2 and 3 is the issue?

Post by **wesk** » Sun Sep 29, 2019 1:33 pm

The weaker spark on the two could cause your issue so have you rechecked their gaps and swapped them with the other two to see if the problem moves with them or stays put indicating a lead or distributor problem?

You've establish a rough idea of fuel delivery but if you really want to roll up your sleeves and solve problems then you really need to buy the needed tools.

2 lbs too much pressure and your carb will flood even if it has the correct float setting. Which brings you to proper float setting. There is an error in the manuals that is still hotly contested by many so called OFFICIANDOS of the hobby!

Finally, wet plugs usually indicate flooding, not a lack of fuel.

Madriver1968 · Post by **Madriver1968** » Sun Oct 06, 2019 1:26 pm

Hi gents - it's been a productive week - I think I'm getting closer.

I bought a fuel pressure kit, and I've checked fuel pressure, it's consistent with the manual.

I replaced the coil, capacitor and bought new plugs. Spork at all four plugs seems good.

I've readjusted the float to 9/64"

I've double-checked the point gap and the plug gaps.

I've double checked TDC, turned it to 5 degrees before, and set the distributor points to just start opening at that point.

Double checked that the choke is closing when the cable is pulled.

When I tried to start it, it caught a bit longer than before but it sill won't run.

Any thoughts as to what I should try next would be greatly appreciated. Thanks in advance!

Bill

jnissen · Post by **jnissen** » Mon Oct 07, 2019 7:47 am

How old is the fuel? Ethanol fuel goes bad in six weeks.

Madriver1968 · Post by **Madriver1968** » Mon Oct 07, 2019 8:53 am

Fuel is new - a week or so old. I do dislike modern gas!

Post by **wesk** » Mon Oct 07, 2019 10:44 am

I bought a fuel pressure kit, and I've checked fuel pressure, it's consistent with the manual.

And that pressure was what exactly?

Have you established what your flow RATE from the fuel pump is?
This test you use a container with quantity marks on it and crank the engine with the fuel line removed from the carb and spilling into the jar.

Have you confirmed the fuel tank vents are open? Both the cap and the vent plumbing.

Have you inspected the entire induction air system for trash, dead rats and etc? Yes this means inside the intake as well.

jnissen · Post by **jnissen** » Tue Oct 08, 2019 2:15 pm

Any time the plugs are wet it’s flooded. You may have primed the motor with some raw gas poured down the carb? In a new rebuilt carb this is standard operating procedure for me otherwise your cranking forever to fill the fuel bowl. If you did prime it with raw fuel you should have the choke wide open and give it half throttle when you attempt to start it. If your choke was on or throttle closed your chances of getting the motor to pop is slim to none.

I apologize up front if this is all common knowledge for you. Just not always known what type of experience others have with rebuilding motors and restarts.

Have you verified that the carburetor fuel bowl has filled properly? Removing the top of the carb is not difficult and will give you a quick visual if the needle and seat were working. If you have fuel, Spark and compression... have you verified yours?

Madriver1968 · Post by **Madriver1968** » Sun Oct 20, 2019 1:00 pm

Ok, it's been a busy couple of weeks, but I'm back with the Jeep. I tested fuel pressure again by running a line from the fuel pump's fuel outlet to a fuel gauge. I think I was off on my reading last time because I was by myself and trying to read the gauge from the driver's seat.

I clearly didn't get a good view. Today, I had help, and at the outlet of the pump I'm getting 2psi when cranking the engine.

I'm going to remove the fuel pump and take it apart and see what's what. I rebuilt it about a year ago, but I can't recall where I purchased the kit. I've seen recommendations for Then & Now. Will be calling them tomorrow.

With regard to Wes' suggestion to look for debris, done and done. The lines are new, I cleaned the tank out myself, installed a new filter, and cleaned everything thoroughly. Both the fording vents and the tank gas cap are open.

I'll keep everyone posted! Thanks again for all of the wisdom!