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lawn tractor runs/mows for 30 minutes then quits

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lawn tractor runs/mows for 30 minutes then quits

Postby jwales » Tue Jul 10, 2018 4:45 pm

Ok so this friend of a friend has a lawn tractor, says it has a carb problem and will take it off and bring over to me to run through my USC. I asked him whats wrong. The tractor starts and he can mow the lawn for about 30 minutes and then it quits. Will not start. even after several hours. It will start after several days and work for 30 again. I do not know the brand but it is around 20 years old. I said wait before you pull the carb as I don't think that is the real issue.... He said he had run the unit with the gas cap loose (venting not the problem). Still same result. even replaced the spark plug. Same results. Sorry not much info here but I was hoping for some ideas to check out.

My thought is to check if it has spark after it quits... (maybe a coil over heating?) Also to check and see if the engine is free of debris (grass clippings/mice nest/etc.)
Anything else to look for before pulling off the carb???
Thanks
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Re: lawn tractor runs/mows for 30 minutes then quits

Postby KE4AVB » Tue Jul 10, 2018 6:07 pm

One other thing which I have been fighting the last couple years with gravity fed systems and that is fuel system vapor lock from boiling fuel. I three Kohler Courages last year and one MTD engine this year that was happening on. As the fuel vaporize it block the normal fuel flow unit the air/vapor was vented.

Just a thought...
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Re: lawn tractor runs/mows for 30 minutes then quits

Postby bluemower » Tue Jul 10, 2018 6:43 pm

since the engine runs ok for 30 minutes, the problem is not likely the carburetor.

My first thought is vapor lock or failed ignition system. When the engine quits, check for ignition spark. If ok, give the engine a small fuel prime to see what happens. These simple checks are quick, cheap, and will give clues.
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Re: lawn tractor runs/mows for 30 minutes then quits

Postby bobodu » Thu Jul 12, 2018 5:17 am

Even if it was vapor lock....that should clear up when it cools down and it should start. Pull the kill wire off the mag.
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Re: lawn tractor runs/mows for 30 minutes then quits

Postby 38racing » Thu Jul 12, 2018 8:29 am

I have had one shutting down due to pinched wires and another due to moveable debris in fuel supply. another was a kohler on old cub cadet. never could figure out the cause. I gave it heavy doses of seafoam as I thought maybe it was sticky valves. that was after I tested for spark failure and fuel flow. been good ever since.
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Re: lawn tractor runs/mows for 30 minutes then quits

Postby bgsengine » Thu Jul 12, 2018 12:56 pm

Just did one the other day, it had bad battery, got a new ignition coil (due to mouse eaten secondary) , and needed valve adjustment. I suspect the problem was (and will come back) due to the bad battery(7.8V after one cranking attempt) causing the anti-afterfire solenoid to close due to not enough volts/amps to hold it open. - bad battery will overtax the charging system, it won't be able to supply enough amps to charge battery and hold solenoid open.
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Re: lawn tractor runs/mows for 30 minutes then quits

Postby KE4AVB » Thu Jul 12, 2018 2:16 pm

Same happens when you have an electric PTO that is partially shorted as it drains the battery to drop out as the alternator can't keep up.

I have repaired three mouse eaten secondary high tension leads this year. All three were on Kohler Commands.
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Re: lawn tractor runs/mows for 30 minutes then quits

Postby 38racing » Thu Jul 12, 2018 5:21 pm

just cleaned a kohler courage.
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