[Healeys] OT: Old Ford tractor acting spastic

[Bob Spidell]

Not Healey-related--although I've heard Healey engines described as 
tractor-like--question for the List wisdom.  I have an old Ford tractor, 
model 851 manufactured in the early '50s, with a 4-cyl engine.   
Compression is good--145+/- on all four--and I've replaced points, 
condensor, distributor cap and plug wires and rebuilt the butt-simple 
Marvel Schebler carburettor (plugs were OK).  After the work, the 
tractor started quickly--after I fixed the 180deg-out distributor 
cap--and ran good for 15-20 minutes with a load from a scraper.  Then, 
it starts backfiring, tries to stall and struggle for a few seconds  
then, if it doesn't die it seems to recover for another 15minutes and 
then the show starts again.  The coil had some corrosion in it so I 
replaced it, with no change.  This tractor ran consistently but very 
poorly under load before my work.

Only thing I can think of is the carb float sticking but it was an easy 
rebuild and I recently rebuilt another with no issues. Any ideas?

Bob