M151 running rich

1959 - 1978, M151, M151A1, M151A2, Technical questions and discussions, regarding anything related to the M151.
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ldj1002
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M151 running rich

Post by ldj1002 » Tue Oct 25, 2022 6:08 am

My M151a2 all of a sudden started running rich, I assumed the needle wasn't seating. Took carb off it was clean, blew it out good anyway. Checked it by blowing and sucking at fuel inlet and all good, needle is seating. Put back on and still run rich. I even blocked fuel line and just before carb ran out of fuel engine run good so that tells me really is running rich. Any ideas appreciated.


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Re: M151 running rich

Post by Blake » Tue Oct 25, 2022 7:17 am

Check the diaphragm in the bottom of the carburetor.

ldj1002
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Re: M151 running rich

Post by ldj1002 » Tue Oct 25, 2022 8:10 am

What will I look for, a hole or split. I rebuilt this carb a few months ago and it should be good but the kit could be many years old. If it is bad how could I rig it to stop it from funning rich as a temporary fix? I think that acts as accelerator pump. I would rather run with hesitation than running too rich.

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Re: M151 running rich

Post by markrdje » Tue Oct 25, 2022 8:23 am

Does the float float in a reservoir in of gas?No gas in it?
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muttguru
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Re: M151 running rich

Post by muttguru » Tue Oct 25, 2022 9:31 am

ldj1002 wrote:
Tue Oct 25, 2022 8:10 am
What will I look for, a hole or split.
Idj,
Here's one that I fixed five years ago. you can clearly see the split.
Ken
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Re: M151 running rich

Post by Rickf » Tue Oct 25, 2022 10:14 am

If the diaphragm is cracked there is nothing you can do, it is pulling gas through the diaphragm and into the main circuit through the vacuum port that actuates the accelerator pump. PM me your address and I will send you a diaphragm I have taken out of carbs I have rebuilt that were still good.
What will do these is is people adding gasoline additives like gas "dryer" to their gas which already has alcohol in it so now the alcohol content is well above the 10-15% maximum the factory rubber can handle. Or, You can get a bad load of gas with far too much alcohol in it. I got 60 gallons of gas in my RV which turned out to have 23% alcohol in it! I can tell you that a carbureted 454 big block does not run well on that!
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

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Re: M151 running rich

Post by svramselaar » Wed Oct 26, 2022 3:09 am

hi

if you don t have a diagram make so cald blind gasket
take the spring out and make a gasket from rubber or material witch can hold petrol
if you do this you have only no acseration pump
i have done this with a Rolls Royce engine from Austin champ

george
1976 ? M 151 A2 AMG MUTT lost in acsedent
1978 M 416 A1 ( parkhurst ) trailer
1970 m151 A2 FORD BUDD tub
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ldj1002
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Re: M151 running rich

Post by ldj1002 » Wed Oct 26, 2022 3:18 pm

I took the diaphragm out and it had a little knot smaller that a pin head and right opposite was a little bitty oblong spot. looked like a defect. I couldn't see any light through the spot and didn't think it was a leak. It must have been leaking there because I made a gasket from a piece of bicycle tube and it idles smooth now but has a bad dead spot. Thanks to Rick I have a diaphragm coming.

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Re: M151 running rich

Post by Snark » Sun Jun 16, 2024 11:47 pm

Hallo

could not find a thread solving problem of my mutt - no problem with starting, but when the engine warms up the idling RPM drops down - it occured in traffic jam - runs without problem but when stops and wait the revs are going down after few seconds and without stepping on gas pedal the engin stops after while. When stepping on gas pedal, to regain revs black smoke gets out of exhaust. Sparks are new - carb and jets are recently cleaned. Guess it could be problem of richness mixture or idle air intake? Did anyone has experiences with same problem?

Thank you very much
David
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Rickf
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Re: M151 running rich

Post by Rickf » Mon Jun 17, 2024 5:39 am

"Carb and jets recently cleaned" This is going to be the key comment here. I will bet you will find one of several possibilities. The float setting is too high, 9/32" is where it should be. The accelerator pump diaphragm has a crack in it or the fuel pressure is way too high. Is your choke set correctly? Loosen cable on carb and push dash know al the way in and then pull it out just a hair, Go to carb and make sure the choke plate is fully open with the linkage and then tighten the cable screw. The choke knob should be just a hair off the dash when you push it all the way in.
Last edited by Rickf on Tue Jun 18, 2024 3:12 pm, edited 1 time in total.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

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Snark
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Re: M151 running rich

Post by Snark » Tue Jun 18, 2024 12:38 am

Thank You for valuable advice - the diaphragm i shall check for sure and also i shall check the choke cable - but how i set the float - its 9/32 (7,1 mm?) from which point to what part of float?
Btw. yesterday evening i was driving it through the city absolutely without problems - probably as it was not as hot and no traffic jam occured

thanks again
Snark in the System

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Re: M151 running rich

Post by Rickf » Tue Jun 18, 2024 3:11 pm

With the top inverted you measure from the gasket to the end of the float, the edge closest to the gasket. To set it is best to pull the pin out nd carefully bend the float arms at the thinner flat area between the float and pivot. Make sure both sides are even. This process can take several or many tries, be patient.

What year is the mutt? If it is an A1 or earlier then you need to have a vented gas cap, not a late style emissions cap from an A2. If it is an A2 it can have either but a non vented cap is stock with the carbon canister under the hood.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

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Snark
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Re: M151 running rich

Post by Snark » Tue Jul 02, 2024 12:03 am

So finally we have opened the pandora´s box
the fuel float setting seemed to be ok - diaphragma also looked like unharmed, but apparently fuel was going through it - so we have exchange it
the problem persisted and it looked the carb is too full of fuell so the inlet needle (the fat short one) was exchanged. The black smoke from exhaust have disappeared and idle rpm are almost stable when engine is warmed. I shall have to test it in traffic jam, but full of hope. Strange thing the needle apex did not look like damaged or worn.

Thanks a lot for all the suggestions and advices
Snark in the System

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Re: M151 running rich

Post by Rickf » Tue Jul 02, 2024 10:29 am

I have seen bad needles that looked good. Did this one have rubber tip on it? They usually do not give problems But I have learned to never say never!

Have you checked the fuel pressure where it goes into the carb? More than 5 psi will give you problems with flooding. Especially in rougher terrain where the floats can bounce. Too much pressure means way too much fuel spurts into the bowl as soon as the float drops a hair. It fill too fast before the needle can shut it off.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone


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