John Deere crawler

Peter M Fallert · Sep 25, 2023

I have recently purchased a 1955 John Deere 40-C crawler.
I'm trying to adjust the carb. The high speed load jet adjustment seems to be working, but the idle speed is mysterious.
No matter what I do , it seems to not have any effect on how the tractor idles. when I rotate the speed handle all the way to the left to idle position the tractor dies.
I've had the carb apart and it was clean as whistle inside, all passages clear. I've read in two place now that screwing the idle screw in richens, and screwing it out leans. Is the screw/needle an air bleed? Advice please. Thank you, Peter

wore out · Sep 25, 2023

Yes. I believe it would use a ''TSX'' series Marvel Schebler carb, and their idle adjustments were ''backwards'', turning the screw IN enriches the idle mixture.

Fritz Maurer · Sep 25, 2023

If this is an updraft carb, you have a leak between the
upper and lower bodies. Try a new bowl gasket. Lay a
straight edge over the outer gasket surfaces and across
the bleed passage on the upper body. If there is any
clearance across the bleed passage, it will not press on
the gasket when the screws are drawn tight. Either need
to have the upper body milled to make it flat or replace
the carb.

Peter M Fallert · Sep 25, 2023

(quoted from post at 13:06:41 09/25/23) If this is an updraft carb, you have a leak between the
upper and lower bodies. Try a new bowl gasket. Lay a
straight edge over the outer gasket surfaces and across
the bleed passage on the upper body. If there is any
clearance across the bleed passage, it will not press on
the gasket when the screws are drawn tight. Either need
to have the upper body milled to make it flat or replace
the carb.

Thank you for the responses. I did replace the gasket. I carefully drew a flat file across both mating surfaces. They both seemed flat. Is there anything else i should be aware of. Peter

wore out · Sep 25, 2023

Be SURE that you have the correct venturi and that it is not damaged so that it doesn't seal in the gasket area.

Also, SOME venturis can be installed upside-down.

I don't think yours can be, but check to be sure.

M-MAN · Sep 25, 2023

Did you run a wire or preferably a
tig tip cleaner through all 3 holes
in the throat? Remove the nozzle
and jets and do the same?

How slow will it run easing back on
the throttle? Could be the idle
speed needs adjustment.

John Deere crawler

Peter M Fallert

New User

wore out

Well-known Member

Fritz Maurer

Well-known Member

Peter M Fallert

New User

wore out

Well-known Member

M-MAN

Well-known Member

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