Mf 165 gas needs choke to run a little

earlier in this sequence, i noticed some red gunky-looking stuff and cleaned the bowl out. then, it seemed to run ok only if i left the bowl holder so loose it would leak; if i tightened enough to stop the leaking, it would start sputtering and then only run with the choke routine. did put in new bowl gasket, and may have helped some.

after cleaning carb (no kit), draining gas tank, new plugs (helped some -- old ones fouled because of the choking), and new coil, the same basic problem remains.

i don't see any cracks in the pot metal glass bowl holder and valve at the bottom of the gas tank.

could there be enough of an air leak between the gas tank and carb to cause this?

how much vacuum is there in this continental gas engine with a zenith carburetor?

in other words, i haven't really got to the problem.

any comments would be greatly appreciated.

thanks

fuel and ignition systems (except condenser) have been gone through and/or replaced.

many of these efforts have marginally improved so that the tractor will run longer at idling speeds than faster, and still requires choke handling to run even to move a round bale to a sick calf in corral.

it will backfire when is about to die. will die quicker at higher rpms, and will idle around with bale on front enough to do some today.

this tractor has been good, but some problem remains.

thanks for anyone who can solve this problem.