8N sputtering under load

OBwan · Feb 13, 2021

50 8N side mount.
Tractor started sputtering under load at full throttle while pulling a blade. Normally for this machine it is an indication the points are going. I replace the points and condenser and it wouldn't start. Saw some crud in the fuel bowl so I removed the bowl, cleaned it out and sprayed brake cleaner into the screen above the bowl. When I opened the fuel valve it filled the bowl quickly. My carburetor has a drain valve on the bottom and verified it drains briskly. Using the adjustable spark checker, no spark. Changed the condenser and verified gap of .025 and now it throws a good spark and started immediately. Next time I used it the sputtering returned. It would smooth out if I feathered the choke. Thinking I need to pull the carb and check the float needle and the jet for blockages. Sound like I'm on the right track?

Rabauer · Feb 13, 2021

(quoted from post at 14:29:21 02/13/21) 50 8N side mount.
Tractor started sputtering under load at full throttle while pulling a blade. Normally for this machine it is an indication the points are going. I replace the points and condenser and it wouldn't start. Saw some crud in the fuel bowl so I removed the bowl, cleaned it out and sprayed brake cleaner into the screen above the bowl. When I opened the fuel valve it filled the bowl quickly. My carburetor has a drain valve on the bottom and verified it drains briskly. Using the adjustable spark checker, no spark. Changed the condenser and verified gap of .025 and now it throws a good spark and started immediately. Next time I used it the sputtering returned. It would smooth out if I feathered the choke. Thinking I need to pull the carb and check the float needle and the jet for blockages. Sound like I'm on the right track?

My guess would be electrical. I recently had a kind of similar situation that turned into a loose coil wire. It was the wire that is similar to the plug wires going to the distributor.

Jim L WA · Feb 13, 2021

Obwan, are you in a cold climate area? The tractor may be running a little lean in the cold, try turning the main jet screw out about a half turn at a time and see if that helps. Having to feather the choke can be an indication of lean fuel mixture of a weak spark.

OBwan · Feb 13, 2021

Virginia, so not real cold. I agree it may be running lean. In the past eight years of use it has performed well in all weather conditions. This is a new development. I appreciate your input and I considered doing that but think something is causing it to run lean so my gut feeling is solve the issue and not just treat the symptom. I haven't needed to touch the carb since I rebuilt it eight years ago so again my gut feeling is it needs some love.

TimInd · Feb 13, 2021

I vote for fuel starvation:
Check the fuel filter screen in the carb. Then, I think also that you might have an intermittent
problem at the sediment bowl. Unscrew the entire assembly and clean it, looking for possible
insects in the assembly that could give rise to an intermittent clogging (a friend of mine had
just that ). Also, try running with the gas cap off, which will tell you if the small breather
hole in the top of the gas tank is glogged. If that does not work, take off the carb, take it
apart including all the jets, and clean it. Finally, check to make sure that the air filter is
not clogged.

showcrop · Feb 14, 2021

Two times what Tim said. You have danced around fuel flow, verifying to the bowl, and that the float bowl drains quickly, but I don't see where you tested flow all the way through from the tank to the carb drain.

8N sputtering under load

OBwan

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Rabauer

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Jim L WA

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OBwan

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TimInd

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showcrop

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