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Electric Tractors
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Got curious about my 72 MF12G engine so I took the carb. off and the head, this is what I found.

Butterfly plate in the intake port.
1 butterfly screw stuck in the head.
Bent exhaust valve.
No sigh of the 2nd screw.

No wonder it doesn't run.
 

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Electric Tractors
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5,639 Posts
Discussion Starter · #4 ·
The bottom end feels tight, no end play and the con rod is tight to.??? The piston doesn't move back and forth much, wall's look good, intake valve is not sloppy. So I'm going to try putting a used exhaust valve from my spare engine in and see how what happens.???
I fixed the carb with parts from the spare engine, I guess the spare engine is now a parts engine, taking too many parts off it already.
If this doesn't work then yes time for rebuild.
 

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Tractorholic
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I just bought a MF10 with a HH120 motor in it and when I rebuilt the carb the inside butterfly was missing, thought someoene just forgot it or robbed it, luckily my nieghbor had an old spare carb. Any thoughts on this guy's becouse my motor seems to run great.
 

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Tractorholic
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I have come across that a few times in engines that have come in. Sometimes the piston or the head or both would be scraped up, but I never find traces of the butterfly or the screws. I've always thought that they finally get kicked out the exhaust. A chipper/shredder with a Tecumseh H50 came in once burning oil, it evidently had run as fine as it needed to. They always run full throttle, so the butterfly isn't really necessary. Unfortunately, the damage its passing did to the cylinder bore and head caused hot spots which resulted in detonation. I'd take off the head and check out the cylinder and the valves just to make sure.
I always use loctite on any of the butterfly screws. On the smaller tecumseh engines like the H70 used in the MF-7, or HSK50's used in a lot of snow throwers, the butterfly's are mounted with only one screw. These are the engines I've encountered this problem in.
 

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Premium Member
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I think you would be alright just replacing the bent valve and putting her back together. If the cylinder walls are not marked up at all. It is amazing was a little cylinder squish can do to a screw LOL.
 

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Tractorholic
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I will pull the head when I get to the motor just to be sure it's not disaster waiting to happen, any recomondations as to anything else I should do while the head is off?
 

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Premium Member
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greencoach47 said:
I will pull the head when I get to the motor just to be sure it's not disaster waiting to happen, any recomondations as to anything else I should do while the head is off?
De-carbon everything. Also check your valve clearances and that the valves seat good. With the head off, that is the time to do any valve work since you are already there.
 
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