JMP Carburetor Problems - Flooding and stalling

1941 - 1945, MB, GPW Technical questions and discussions, regarding anything related to the WWII jeep.
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JMP Carburetor Problems - Flooding and stalling

Post by pmhslight » Mon Aug 12, 2019 10:29 am

Hi

I have a 2 +/- year old JMP Carb on my 1942 Willys mb. Last week the jeep stalled as I was driving down the road at 30+MPH and I was not able to restart it. I pushed it to the side of the road and opened the hood and noticed a strong smell of gasoline. After about 1 hour, with the pedal to the floor, I was able to restart the jeep and then noticed gasoline gushing out from the carburetor. I quickly shut the jeep to avoid a fire (it was spilling onto a hot exhaust manifold) and had the jeep towed. Once home, I disconnected the fuel line to the carb, started the jeep and ran out all the fuel in the carb bowl. I hooked it back up, changed the fuel filter, and restarted the jeep. It ran fine. A few days later while driving the same thing happened and the carb flooded gasoline all over.

My question is does anyone have any ideas? I am NOT a carb expert by any means. As the carb is newish and this problem only happened recently, I am not too sure. Prior to happening, I have been driving the jeep on a fairly regular basis so it has not sat. I put lead substitute in the fuel and stabilizer when parking it for the winter.

I am thinking that the float needle or seat may be stuck / clogged / etc? Again, I have no experience with a carb so not sure where to begin in terms of dismantling it. Should I sent it out for a rebuild or purchase an original one that was rebuilt instead of the JMP (joes motor pool one) that I am currently using? I am not opposed to purchasing an original one if there was a reasonably priced one and it would solve the problem?

Any help would be very appreciated. To have the jeep stall out while under speed was quite frightening especially as I was in the midst of other moving cars.

Thank you in advance as always
Jason

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Re: JMP Carburetor Problems - Flooding and stalling

Post by dinof » Mon Aug 12, 2019 3:02 pm

Dirt or rust or debris in the fuel tank, strainer, fuel pump will always create symptoms that you might think that there is something wrong in the carb. The needle/seat in the carb can easily get held open by some foreign matter. So, clean out the carb especially in the needle / seat area AND make sure the tank & strainer are very clean. If the situation persists, than it might be good to change the needle & seat.
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Re: JMP Carburetor Problems - Flooding and stalling

Post by Joe Gopan » Mon Aug 12, 2019 4:17 pm

Which type fuel filter? Inline or OEM AC T-2?.
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Re: JMP Carburetor Problems - Flooding and stalling

Post by privatebrian » Tue Aug 13, 2019 10:23 am

I had the same problem, but it was on a W-O carb. Turned out the float had a pinhole in it and was partially filled with gas. Therefore it didn't really float and the needle valve didn't close into the seat. You could hear the fuel sloshing around inside when shaking the float. I replaced the float, didn't want to attempt soldering over the hole.
Best of luck,
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Re: JMP Carburetor Problems - Flooding and stalling

Post by Joe Gopan » Tue Aug 13, 2019 3:25 pm

After you get it running smooth, switch to Ethanol Free gasoline, your Jeep will make you smile, there is a difference. I add Lucas Fuel conditioner for added effect.
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Re: JMP Carburetor Problems - Flooding and stalling

Post by Chuck Lutz » Tue Aug 13, 2019 4:45 pm

The JMP Carbs have one slight problem; they can't be road-tested very easily and then sent from China to the USA without Homeland Security freaking out when the sea-freight container smells like an "accelerant" used for arson fires. At least I don't think they do....

However, I believe you hit on the problem in that next to last paragraph....some grit or crap is keeping the needle valve from closing and flooding the bowl and overflowing onto the manifold.

You can address this problem by removing your carb and cleaning it out but the source of the problem needs to be addressed.
1) do you use the firewall filter or an in-line aftermarket one
2) if you do...does it have the original brass strainer or a paper filter in it
3) has the gas tank ever been removed and thoroughly cleaned of any and all grit/crud/crap
4) have you ever used a jerry can to put fuel into the gas tank without checking to see if the internals are rust free
5) have the fuel lines been "blown out" (cleaned)
6) any chance your fuel pump diaphragm is failing and allowing small particles to enter the carb

The history of the jeep is important and how long a particular problem has persisted (time/miles). Any recent repairs or modifications would fall into this category.
Chuck Lutz

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Re: JMP Carburetor Problems - Flooding and stalling

Post by artificer » Tue Aug 13, 2019 5:12 pm

Flooding is caused primarily due to a carburettor needle & seat 'related' issue.
What happens when all is working properly is the float rises on top of the fuel until it closes the needle on it's seat.
This closing causes a back pressure against the diaphragm return spring & 'simplistically put' puts the fuel pump in neutral so there is no fuel delivery.
As the fuel level drops the needle & seat open, so the load is removed from the diaphragm return spring & the fuel pump goes back to pumping, until the needle closes again.

Understanding the above will help diagnose/pin point the issue/s:
1. Dirty or worn needle & seat
2. Float level set too high [or sometimes too low]
Some floats have 2 adjustment tabs high & low.
Low is to stop the float bottom wearing out & the needle coming out too far & jamming open.
3. Float ingesting fuel & sinking. Usually along a soldered joint.
4. Fuel pressure too high & not allowing the needle & seat to close off to put the fuel pump into 'neutral'.... [fuel pressure is totally governed by the strength of the diaphragm return spring].
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Re: JMP Carburetor Problems - Flooding and stalling

Post by wo2jeeper » Wed Aug 14, 2019 2:59 am

Needle and seat clogged, not only on JMP but also the ones in the repro master kit. Just clean and go. Not necessary to make an endles what caused it discussion.

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Re: JMP Carburetor Problems - Flooding and stalling

Post by CLeBlanc » Wed Aug 14, 2019 3:35 am

I recently experienced this issue as well. I believe it is due to the rubber tipped needle/seat that comes with the new rebuild kits mixing with ethanol fuel. I never had an issue until I used "regular" gas at the pump. I used to use nothing but 100LL, but the airport fenced their pumps and I can't fill up there anymore. No other ethanol free options in town either. I cleaned out the needle/ seat several times and after one good run, the carb would flood again. I switched out to an NOS Carter all metal needle/seat and have not had an issue. Take that for what it's worth.

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Re: JMP Carburetor Problems - Flooding and stalling

Post by Al Rains » Wed Aug 14, 2019 7:03 pm

Have you tried purchasing the av gas for use in your race car? That is the way I have to purchase LL100 for my Corvettes. I carry 4-5 5 gallon cans marked Race Gas Only to the local airport for my "Saturday night race car" and purchase it without an issue.
vetteman

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Re: JMP Carburetor Problems - Flooding and stalling

Post by CLeBlanc » Wed Aug 14, 2019 9:07 pm

I'll have to give that a whirl. I used to just sneak in under cover of darkness and pay at the pump using a tail number off the flight line.... :lol:
"All that is necessary for the triumph of evil is that good men do nothing" - Edmund Burke
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Re: JMP Carburetor Problems - Flooding and stalling

Post by Jeff H » Thu Aug 15, 2019 4:02 am


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Re: JMP Carburetor Problems - Flooding and stalling

Post by Chuck Lutz » Thu Aug 15, 2019 9:58 am

One of the obvious bonuses to reading about the problems someone has is the fact that not only the SOLUTION to the problem is discussed and if several are possible, they are run down for the OP to check on.....but the details of what CAUSED the problem to occur in the first place are posted and how to run them down in logical manner.

Contrary to the opinion of some, it is a teachable moment as to what causes these issues that often pop up on not only a long-running engine but on an engine with new/rebuilt parts on it like this one. We know it is a brand-new JMP carb and the posts have generally pointed to a needle/seat issue more than other possibilities but those other issues were kindly discussed as well by contributors.

Then the more detailed posts about what CAUSED this problem were included, much to the dismay of at least ONE person who obviously feels that it isn't important for you to know what CAUSED the problem, just what it most likely is.

That ain't how it usually works here though, Thank God...
Chuck Lutz

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Re: JMP Carburetor Problems - Flooding and stalling

Post by pmhslight » Fri Aug 16, 2019 10:38 am

Hi All

Thank you for all the helpful ideas!

So to give an update:

1. When I opened the fuel filter bowl (yes I use it) I noticed that there was some debris in the bowl. Not a lot, but enough for me to notice it. I don't know how long it has been there as I have previously never opened it (shame on me). The fuel filter was the original brass strainer one. I have subsequently cleaned out the bowl, removed the original filter (placed it in storage) and inserted a cartridge filter.

2. I took the carb off and unfortunately needed to send it to a carb shop. I am not experienced enough with carburetors and don't want to make the situation worse.

3. I inspected the inside of the fuel tank as best I can and I don't see any obvious flaking.

**4. when I took the carb off, I noticed puddles of fuel in the bottom of the intake manifold. Is this normal? Should I attempt to clean it out? Im not sure if this was deposited there when it was flooding.

While I wait for the carb to be looked at (I asked them to tell me the cause of the flooding and if they find debris in the there), im not sure what I should do regarding the fuel tank. It seems very labor intensive to drain and remove the tank and have it re-lined if it doesn't need to be. Unfortunately I really don't have a way to know. Being that I have a new cartridge fuel filter, I am assuming that that would catch any particles and prevent this from happening again? Am I incorrect on this assumption?

My fuel pump is of an unknown age as it was there when I purchased the jeep. I have previously driven the jeep with the JMP carb for about 1-2 years without issue.

Thank you again for your help!
Jason

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Re: JMP Carburetor Problems - Flooding and stalling

Post by Chuck Lutz » Fri Aug 16, 2019 11:06 am

Time to clean out the complete fuel system from tank, to strainer, to flexible line, to fuel pump to carb to find out where the crud is being introduced into the system. My guess is the tank. It would need a really GOOD cleaning out and a determination if the insides are rusting/flaking off or, if there is some crud in the fuel itself that got picked up. A dirty jerry can, a station that has older tanks that may be near empty or other causes come to mind.

The TM 9-803 I think mentions how to disable an engine if the vehicle must be abandoned in the face of the enemy advance....dump sand in the gas tank!
Chuck Lutz

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Bantam T3-C 1947

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