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Thread: My M38A1 is hard to start

  1. #1
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    My M38A1 is hard to start

    I have had my M38A1 (1953) running over the past couple of years but it has been hard to start at times both while cold or hot. Since this vehicle is at my property, I only have a chance to run it every few weeks. I am not an experienced mechanic, I learn by doing and redoing. The vehicle had a Carter YF carb on it when it was purchased. I was given a YS carb with the vehicle, rebuilt it, and installed it on the engine. The engine started ok but ran rich. My grandson and I stalled the jeep while driving and I have not been able to get it started since. I finally have time to work on it and wanted to know which carb (YS v YF) is the most consistent performer for the M38A1. I would appreciate thoughts on how to make my engine more reliable starting. I replaced spark plugs and cables and plan to clean and adjust points and install a new condenser. As far a I can tell, the fuel pump is original.

  2. #2
    Super Moderator gmwillys's Avatar
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    Welcome Col. Ken,

    The YS950S is the correct carb for your A1. It appears that you are having an issue with the float/needle and seat. Since you have had it running, (albeit running rich) it sounds like you have picked up some gunk from the fuel tank. The needle is most likely not seating properly to cut off the supply of fuel from the fuel pump. The other possibility is that the float may have developed a leak, and is not as buoyant as it should be, and allowing the float bowl to over fill. With the latter, it isn't as likely because you were running when it became flooded. A float would fail over time rather than all at once. Rust of dirt from the tank would be the most likely the culprit. Since you are probably filling the tank with a gas can, you may need to check the cleanliness of your can. Another thing to think about is the quality and grade of fuel used. Ethanol is not friendly to the internals of your fuel system. I know I have one gas station in our town that has a pump for 100% gasoline, and I have not had any issues with fuel and fuel storage. Another option would be to find some additive that neutralizes the effects of the ethanol.
    https://lucasoil.com/products/fuel-t...th-stabilizers
    Once you get the engine to run again, then it will be wise to set the air/fuel ratio to fine tune the carb. Turn the air/fuel screw all the way in, and back it back out two turns as a starting point. Turn the screw in to lean the mixture, out to richen the mixture. The screw is located on the base of the carb.
    As long as we are on the subject of fuel additives for our Willys, you may want to look into a lead additive as well. Since leaded gas is a part of history, the lead needs to be replaced to help cushion the valve train within the engine. This is important unless the engine was rebuilt using hardened valve seats, and stainless or hardened valves. Then you don't require the additive.
    Cleaning the points will be a good step to take as well, but a new condenser is a must. LarrBeard on this forum, has a good write up on the importance of the condenser. A faulty condenser will mask problems that make you think that there is other problems. Poor spark can lead you to think that the carb is set too rich, but in actuality, the spark is not hot enough to burn the supplied fuel.

  3. #3
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    Thank you! It will be a week or two before I have a chance to work on my jeep. FYI, I switched to premium gas on a recommendation from my cousin who restores cars also. Will keep you advised.

  4. #4
    Super Moderator gmwillys's Avatar
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    Sounds like a plan. In my opinion, your cousin is half correct. Many people who deal with vintage equipment will use a high octane fuel in their engines, but most of them mix regular 87 octane fuel and mix it with high octane aviation fuel. The result is not so much to boost performance, but to add lead through the avgas. The F134 was designed to run 63 octane, due to the availability of fuel on the battlefield. Do you need avgas? No, buy the lead additive and mix it in when you add fuel.

  5. #5
    Senior Member TJones's Avatar
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    I had a motor with fuel injection that ran on methanol and the linkage in the throttle body would always stick open due to lack of lead or lubricants in the fuel ”not good” and an Ole timer told me to dump a pint of castoroil in with the fuel and it would help lubricate everything.
    Just a suggestion.
    Last edited by TJones; 12-20-2018 at 07:31 PM.

  6. #6
    Super Moderator LarrBeard's Avatar
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    You asked about Carter YF vs. Carter YS carburetors.

    For the M38A1, the YS is indeed the correct unit. It has the right-angle air inlet and linkages in the right places. Both the YF and YS will deliver the correct amount of fuel in the proper proportions to the F-134 engine.

    GMWillys got to the subject first, but for an additional 1-cent’s worth I agree.

    Look at float, needle valve and seat. You mentioned that the fuel pump looks original. That’s a good observation because we have seen several cases where a new or rebuilt fuel pump will deliver higher fuel pressure that the YF or YS float and needle can regulate. Those carburetors are happy with 1-1/2 to 2 PSI fuel pressure. We had to add a fuel pressure regulator to the ’48 to get down to that. Is there a fuel filter anywhere in the line? Since I have a new, plastic, tank - mine is between the pump and carburetor, but between the tank and pump is a good idea if you have an old tank that might have crud in it.

    Since your M38 sits a lot, Seafoam or another fuel stabilizer would not be a bad idea. It doesn’t need mid-grade or premium fuel – 63 octane (try to find that!) was the specified fuel rating. Modern 88-octane is already overkill. I also agree about the lead additive. In addition to being an octane (anti-knock) additive, tetraethyl lead ended up as a coating on the exhaust valves and seats to protect them from high exhaust gas temperatures. Now, you’re not going to beat the F-134 that hard in most applications, but unless you know that the valves and seats have been upgraded for unleaded fuel, it’s just a good idea.

    A bad condenser will give you a weak spark that won’t burn fuel – so it makes it look like the carburetor is running rich. We fought this for a month on the ’48 2WD truck until the old guy told us to change the condenser.

    We objected; “But it’s a new distributor”. Old guy replied “Do you want to argue or do you want the d**n thing to run?” Since arguing wasn’t going to get us anywhere, we changed the condenser (the ground clamp wasn’t connected to the case) and it has started and run well every time over the last two years.

    The screw adjustment for mixture sets idle mixture. Once you get running, mixture is set by the metering rod and orifice inside the carburetor. Not much can go wrong here unless someone has been in there doing new and improving.

    I’d suggest that you check the needle, float and seat in the carburetor, change the condenser, recheck point gap and clean the plugs if they have any running rich time on them. Let us know how our advice works …..

  7. #7
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    Thank you all. I took my carb apart, cleaned it, put it back together and mounted it yesterday. I will add the lead additive and install the new condenser as soon as I can. My vehicle was surplussed out of the Corps of Engineers (date unknown) and passed through a few hands until I purchased it. Info from the previous owner indicated a partial rebuild on the engine but I don't know to what extent. I will add an inline fuel filter. The metal gas tank had been replaced by a plastic boat tank when I purchased the vehicle. This is my first post and you all have been very helpful! More to come I am sure. Merry Christmas and Happy New Year!!

  8. #8
    Super Moderator gmwillys's Avatar
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    Col. Ken,
    Merry Christmas to you! We look forward to seeing your progress, and giving any advice that you seek.
    Best regards,
    GM.

  9. #9
    Super Moderator LarrBeard's Avatar
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    Merry Christmas and a Happy New Year to you too!

    Quote Originally Posted by col_ken View Post
    More to come I am sure. Merry Christmas and Happy New Year!!
    Yep, an old Jeep is like a boat or an airplane - there is always something to look after or putter on.

    Well, I've got to go now - I have to get my sled ready for another couple of hundred thousand miles tonight!
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