860 running rough when hot

Tiger Joe

Member
Got a call from my dad yesterday. he was brush hogging with our 860. said after about an hour, machine developed a miss. seemed to only happen with a load on the motor- either cutter running or coming up a steep hill.

When we cut with the machine a few months ago it developed a slight miss after cutting a bit, and after that we did a tune up due to not knowing how old everything was. Tune up was done with all good parts, no tisco junk.

tune up:
new autolite plugs
points
cap
rotor.

All done roughly 1 1/2 months ago and ran fine with no load till now. we hadn't cut with it since, but drove it around and its ran just fine.

When he called me, he had no tools. he pulled the gas cap to check vent, no change. when he got back to his house he gapped a plug wide (he said maybe 3/16) and said he had good spark with that.

I'm thinking possible fuel delivery problem? First idea is to pull plug outta carb bottom and check flow.

any other ideas?
 
give a tug of choke.. not full pull.. but see what various levls of choke do.. if it helps.. may be lean, thus fule delivery.

this assumes spark is good when hot.
 
(quoted from post at 09:17:33 10/08/15) give a tug of choke.. not full pull.. but see what various levls of choke do.. if it helps.. may be lean, thus fule delivery.

this assumes spark is good when hot.

ah ya, forgot all about that yesterday when I talked to my dad.
 
Yep as sound said do the choke thing. If that does not help you might want o take a look at he plugs and see how they look. I have found the new auto lite plugs are now since going tot the land of almost right are junk. I have switched to NGK 3112 plugs. Of of course it could be a valve adjustment needed
 

yeah left condenser out of first post. that was changed too.

So if its spark related, I'd go to coil. again unknown age since we just got the tractor.
 
Boiling gas in hot conditions. Reroute or change the fuel line; we moved the muffler out from under the gas tank just a pipe in there to give
more room for air to circulate.

Coil overheating, we got longer bolts and moved it out an inch with a block of wood spacer behind.

Check the new condenser and coil, I've had new out of the box be worse than what I replaced....

If it never did this before and not that hot and nothing else, ours (a 960) did that when the distributor wore out. Too much slop, and it bypassed
hot vapors into it from the crankcase. Worked cold, but didnt run at all hot.

Paul
 
Check the archives, this model has the fuel line routed behind the manifold and tends to over heat the fuel causing boiling in the gas line? I rerouted the line in front of the engine and it helped, Also use gas without corn which boils at a higher temperature. Keeping the tank full also helps.
 
Finally got to look at the tractor over the weekend.

had a miss while cold now, so started poking around. short version- the stud on the distributor, the insulator inside had cracked so it was shorting out. also looks like the strip that connects the stud to the points inside was barely there.
 
ok update here.

Got the new insulator in the distributor. Tractor runs now but has a miss still.

Seems to be spark related not fuel. Pulled plug from carb and had nice flow and sitting there in the garage with the tractor missing pulling choke makes it worse.

My dad worked on it today. He said it has spark that jumps a spark plug gapped wide- probable 3/16. Spark doesn't seem very strong though.

I'm hoping to get out there Sunday to go thru it. I've got all my old spare parts I can swap in to test. Being that the spark seems weak across all cylinders, and the points are gapped properly, I'm thinking new condenser is bad maybe. Already tried swapping coils and that made no difference.
 

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