Farmall M Carb

Trent Couch · Jan 28, 2019

I?ve got a Farmall m with 4? flat top pistons a 8060 head and a new main seat I got from McDonald Carb it said that the seat may need to be drilled to size and I believe so because my plugs are starving for gas I believe the size it is now is .045 what size should it be? And also what about the main discharge jet what size should this be I got a kit and I?m not sure if it?s the right size?

charlieu · Jan 28, 2019

I had to get out my GSS-1309 service manual for Carburetor Specifications to find the size of the Main discharge metering jet.

Carb number 47387DC has a .059 hole
Carb Number 58553DB has a .058 hole

These are the two carbs that I show for a Farmall M. If your carb has a different number, let me know and I'll check the book.

D Slater · Jan 28, 2019

IIRC. .0545 was the original size for a gasoline carburetor, but for that M around .058 to .061. Most of the aftermarket kits have sold the one size discharge nozzle for years until most end up with around the same size in them. Do you now if the discharge nozzle tip is around .106 diameter or .112 you have. Can't find my notebook with the 3 hole sizes for some discharge nozzles this evening. SM gas carburetor nozzle works okay for the 4 inch flat tops but they are discontinued last I looked.

Trent Couch · Jan 28, 2019

Thank you for the info I will locate a drill bit that size and bore it out a touch. As for the discharge nozzle I?m not sure I will have to look tommorow to find out I just didn?t have any specs on what they should be. You wouldn?t happen to have an idea what the idle jet size should be do you?

Trent Couch · Jan 28, 2019

Thank you for your reply!

D Slater · Jan 29, 2019

Idle jet hole diameter was .025. Some power improvement kits and fire crater kits used .021. Find the most M gas carburetors around this size I have messed with 50983DD carburetor as a example, main seat .059, air bleed .055, idle jet .025 or .021, nozzle tip ID .106 to .108, top hole .042, middle .046, bottom .055. Fire crater kits have higher numbers other than the idle jet. But find all kinds, think .080 is the biggest main seat I noticed and a 1/16 drill bit size is common. Discharge nozzle tips .136 and holes in side up to .070. Check the air passage up to throttle shaft bushing in throttle body. If it was plugged in the past several other changes were done to the metering. You can stick something up a hole in bottom of throttle body and measure to see if it reaches the OD of bushing. Should stop about 1/2 inch or so before bushing if plugged.

Farmall M Carb

Trent Couch

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charlieu

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D Slater

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Trent Couch

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Trent Couch

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D Slater

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