Cub dies after 20-30min

[Greg]

Hi all,

This forum was very helpful when I rebuilt my 1950 Cub several years ago. For the last year or so I have a problem. Cub starts easily, runs smoothly but after 20-30min of mowing (and easy mowing at that) the rpm slowly dwindles and it dies. No surging or sputtering, just slows down and dies. When I try to crank it, it sounds "tight" in that the starter engages, but doesn't seem to be able to turn the motor over. Then if I wait only 1-2 min it will start up again, but then after less time (10-15min) it dies again. If I continue to work with it the time running gets shorter. There is gas in carb when it stops. I have gone thru the fuel system/carb and everything seems ok. I tried opening the gas cap when it would slow down to see if the vent was not working, this doesn't prevent it from slowing and dying either.

Could this be a problem with it overheating and getting 'too tight'? Fan is turning and coolant level is ok.

Any assistance is appreciated.

[Jim Becker]

Have you checked for spark after it dies? If it is weak or gone, you probably have a failing coil or condenser.

[Barnyard]

Jim, I thought the same as you, but when he said, "When I try to crank it, it sounds "tight" in that the starter engages, but doesn't seem to be able to turn the motor over, I ruled out the coil. Shouldn't the engine crank over even when the coil is going bad?

[Jim Becker]

I'm thinking the slow cranking may be a separate problem. The starter may need work. If the engine is really tightening up, something else, not fuel or ignition is going on.

Greg, do you have a hand crank so you can check by hand whether it is really tightening up?

[Gary Dotson]

If it actually tightening up, check and lube the fan hub. It could be trying to lock up.

[Greg]

I do have a hand crank, will carry it with me next time I'm mowing and check that. I'll also lube the fan hub and see if that helps. I think I checked for spark last summer, I'll check that again-- though by the time I get my spark tester on it, it may be ready to run again. I wondered about the coil but the fact it starts within a minute or two, I thought wasn't enough time for the coil to 'cool down'. ????

[Don McCombs]

In addition to the previous suggestions, when it quits, feel the coil and see if it is hot.

[Greg]

Thinking about the coil.... I had put that aside based on the way in which my cub dies. I can hear the rpm slowly decline over 30-60sec, then it quits. I thought the coil would cause it to suddenly shut off-- am I wrong (I often am about electrical things). It just seems to 'grind to a halt'- no sputtering or surging, just slows down. Even when I push in the clutch, play with the throttle-- nothing helps once it starts slowing down (RPM-wise)- it just dies. Then will start again after a minute or two, sometimes 3min. I plan to check the hand crank next time I mow (if we get any rain!).

[Eugene]

Thinking about the coil.... I had put that aside based on the way in which my cub dies. I can hear the rpm slowly decline over 30-60sec, then it quits. I thought the coil would cause it to suddenly shut off-- am I wrong.

Coil could be/likely slowly breaking down. Doesn't have to suddenly break down/quit functioning.

Also likely, as Jim Becker suggested, that you have more than one problem.

[Donegal Cub]

Thinking about the coil.... I had put that aside based on the way in which my cub dies. I can hear the rpm slowly decline over 30-60sec, then it quits. I thought the coil would cause it to suddenly shut off-- am I wrong (I often am about electrical things). It just seems to 'grind to a halt'- no sputtering or surging, just slows down. Even when I push in the clutch, play with the throttle-- nothing helps once it starts slowing down (RPM-wise)- it just dies. Then will start again after a minute or two, sometimes 3min. I plan to check the hand crank next time I mow (if we get any rain!).

Greg you’ve had good suggestions, but my money is on a faulty coil.

[ShawnAgne]

I'd have to go back to 2016 threads but if I'm remembering correctly mine did the same thing and was the coil.

[NJ Farmer]

You say the engine is tight when it dies…..is the Cub overheating/lack of coolant?

On think I would/might check….when was the last time the radiator was removed and the bottom fins (pickup tubes) on the bottom of the radiator are clear and clean to allow for circulation of coolant.

Maybe the motor is getting too hot and not necessarily the radiator side of the world but the engine side….

Just a thought!

NJ Farmer

[CSA_CUB]

This sounds exactly like what mine was doing last month. I had replaced the coil, points, and condenser. After Don's suggestion, I removed the carburetor and cleaned the inlet screen. mine has been running ever since with no problems.

[Cubfriend]

I would also check to see if the gap is correct on the points or if they are corroded. It could also be the condenser as a possible problem. Point gap on distributor is .020, point gap on magneto is .013

[Greg]

UPDATE: I had a chance to mow again, it died after 30min of mowing, I jumped off and used hand crank- turns easily. Coil was not hot at all to the touch-- I left my hand on it for a while and it never felt hot. I cleaned the inlet screen of the carb before this last episode so I don't think that is at fault. What about the gas cap? I'll re-check points, though it runs great before it dies, and starts again within a minute or two of dying. Thanks in advance for your thoughts....