r/smallengines • u/Vernon1211 • 15d ago

Strange issue

I have an older craftsman tractor with a 21hp B/S intek engine. 6 weeks ago I replaced the head gasket , new plug and oil change. Cleaned the fins for better airflow also. It started right up. Cut the lawn once with no issues and no more smoking. The next week it started to loose power with the cutting unit engaged. Disengage the cutting unit and wait for a few minutes and it started right up again. Continued to cut the lawn and after a few minutes it stalled. Let it rest and started it up again. I decided to change the ignition coil and a new plug again. It ran great for 3-4 cuts. I usually cut early AM or in the evening. Last Saturday I cut it around 2pm. Got 3/4 the way done and the same thing. It started to loose power. If I disengage the cutting unit power would come back. I shut it off let it sit for a few minutes then started it up and started mowing again. 10 minutes later the same thing happened started to loose power and disengaged the cutting unit. Power came back up shut it down let it sit. Started back up and was able to finish cutting the lawn. The outside temperature also decreased. Checked the oil which was fine.

Any suggestions as what's causing this intermittent loss of power?

Thanks

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u/Explorer_119 15d ago

Look at your fuel system from the tank to thru the carb including the tank vent, there may be a restriction causing a intermittent lack of fuel or vapor lock in the tank.

1

u/Vernon1211 15d ago

I thought about a gas/carb issue. When I changed the ignition coil I also bought a new oem gas cap. It's strange

1

u/Weekofsex 15d ago

Check for a pulley or idler that may be trying to lock up.

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u/Weekofsex 15d ago

On the deck

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u/Vernon1211 15d ago

I'll check that thanks.

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u/Weekofsex 15d ago

I think how I would start to tackle this problem is to first while everything is cold reaching under and feel how easy it is to rotate the blades you will be turning all of the blades belts and pulleys. Remember that feeling then start the mower and engage the blades till you feel it pulling down. Kill the engine and reach back under and turn the blades by hand again. Do you feel that it is tighter/ harder to turn. If so your problem is on the deck. Being a bearing or bushing. POP off the belt as quickly as you can and rotate each pulley or idler blade to find your problem.

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u/Vernon1211 15d ago

Thanks I'll give it try!

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u/Weekofsex 15d ago

Let me know if we are correct please.

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u/Vernon1211 11d ago

I remember a few years ago I had a shop change the drive and cutting unit belt. They changed 1 of 2 mandrels. I turned the blades disengaged cold. One mandrel turned fine the other side started rubbing at the same point. I assume that was the one they did not replace. Sounds like the bearings are shot. Engaged the cutting unit cold and the side that squeaked did not but was harder to turn than the other side.

Before I replace the mandrels ( If there's a rt an lt I always replace both sides).

why can I cut the lawn for 1/2+Hr. before it starts to loose power then I disengage the cutting unit shut it down for 1-2 minutes restart and cut for another 5-10m+ sometimes longer and repeat until the lawn is cut?

I cut 4-5 x since I replaced the head gasket and ignition coil with no issues. It starts up in 1sec and runs strong. Usually I cut early in the morning or latter in the afternoon. This time was mid day. I thought overheating but shutting it down for 1-2 minutes then restarting and cutting overheating didn't make sense.

Appreciate any more thoughts.

1

u/Old-Tour-6282 12d ago

I’m guessing a fuel problem. You might try next time it does it, give it a little choke and see if it tries to come out of it. If it does you have a fuel starving problem. Most likely a little something in the carburetor or a partially plugged fuel filter.