M151A1 Zenith Carb Problem

[Charlie 6]

My M151A1 starts and runs great. Problem is when I am in 4th gear driving 40 mph I let up off the gas and push the clutch in to down shift to turn off the road and the engine quits. Same thing going down hill I take my foot off the gas pedal and it stalls. The electric fuel pump is new also has new plugs and just converted to electronic ignition. Any ideas?

 

[vtdeucedriver]

Idle too low?

 

[natem]

This is a very common problem, even with new carbs. Just set the choke till it bumps the idle up a little. It will run fine.

Nate

 

[Charlie 6]

Thanks for the replies, It idles fine when sitting, I will bring the idle up a little more by pulling out the choke a little. I will take it for a test drive and see what happens.
Thanks any more suggestions please let me know.

 

[poppop]

Everytime mine did that I had picked up a little trash in the idle jet. Took carb apart and blew out and corrected problem. They all need to run with the choke out a little.

 

[Charlie 6]

I am planning to put some Sea Foam in the tank, when I installed the new electric fuel pump the tank was clean inside so no worry there.
In the early 1980s I rebuilt a couple of M151A1 Carbs when I was in the army.
B Co 701st Maint Bn, 1st IDF Panzer Kaserne, Boeblingen, Germany.

 

[Westech]

I drilled out my jet to .0055 and set the choke to 25% on all the time. My M151 runs great and starts great now.

 

[steelypip]

Has anybody ever put a decent carb on one of these engines? This sounds like a lot of hacks to get around bad engineering...

 

[Charlie 6]

I drove a M151A1 and A2 in Germany from 1979 to 82, even on the autobahn, don't remember any carb problems.
I also was issued a new Mutt that came out of Prepositioned Materiel Configured to Unit
Sets (POMCUS) from England with only 15 miles on it, It drove/ handled/ sounded like an old jeep.

 

[vtdeucedriver]

Turn the idle up a bit and you will be fine with your current problem. The 151 always seems to have issues on how they run. I would not worry about setting the choke just yet, That usually fixes another problem

 

[poof]

I finaly got my Valves adjusted.. what a diffrence I have vacuum now too from that adjustment..
J.P.

 

[bullfrog1234]

I have an issue with mine, it will idle fine, but it spits and sputters when i press down on the fuel petal. Lately it back fires through the carb. I am in the process of cleaning the carb and checking for vaccum leaks with zero leaks that I can find. I even checked the timing and that has not fixed the problem. I have not drilled out the jets in my carb because it is brand new and I was hoping this would fix the problem.

 

[Charlie 6]

I was able to pick up a new carb at a fair price and slapped it on, I set the choke to what the 20 manual recommends and it runs perfect now. It also has better pick up and top speed. Thanks for all your support.

 

[bullfrog1234]

That is great to hear! It sounds like the old one needed work on the jets. Maybe worth keeping it and working on as a spare.

 

[Charlie 6]

Definitely keeping it and when I have the time see about rebuilding it.

 

[bullfrog1234]

it is easy. I dipped one of mine in the carb cleaner and it removed all the crude. The only thing left to do is check the jets. The seal and repair kits are cheap.

 

[bazookajoe]

once the carb is rebuilt properly you dont need to run with the choke out. I put a tank liner product in my gas tank to contend with particulate corrosion. The rebuild the carb... correctly, by making sure the top of the float chamber is flat and seals well and be sure to seal around the long brass jet

 

[bazookajoe]

You also need an auxilury fuel filter. Also check your fuel pump for corrosion issues in the check valves

 

[m38inmaine]

There is an ad in mvm from Brooks Engine Service in FL advertising M151 carburetors that have been rebuilt as to eliminate the usual problems.

 

[Rainman]

Zenith's are a bit finicky but I don't run with any choke, and you shouldn't have to. You have other gremlins to chase if your having to jack up your carb to compensate. Red River has NOS Zeniths for $150, soft and hard rebuild kits are cheap and readily available. I had some hiccups in the carb after the local Memorial Day Parade and the new carb fixed me right up. No backfires from either end.

Can never have too many fuel filters on military vehicles. Frontline might be one of the cheaper suppliers on rebuild kits if I remember right.
Rainman