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high compression & backfire

shamu62's Avatar

Join Date: Jun 2006
Posts: 3

06-03-06, 09:02 PM   #1  
high compression & backfire

My neighbor gave me a nice Craftsman mower with a 6.5 hsp Tecumseh that wouldn't start. I found the flywheel key shaved and the blade hub was missing. Put in a new key and tried to start it without a blade. It cranks very hard and feels like it has high compression. It won't start, but will pop back through the carb.

I suspected the mechanical compression release wasn't working so I opened it up. The flyweight moves freely and I don't see any evidence of wear on the flyweight tab. The valves and valve seats all look good, but the valves aren't adjustable.

Ideas please?

Thanks in advance.

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shamu62's Avatar

Join Date: Jun 2006
Posts: 3

06-03-06, 09:06 PM   #2  
more information

I forgot to mention that with the spark plug removed, it spins over like it should. With the spark plug in, I can hardly crank it with the pull rope.

nap's Avatar
New Member

Join Date: May 2006
Posts: 4,163

06-03-06, 09:19 PM   #3  
When you talk of the flywheel key being shaved, are you speaking of the key on the blade hub or the key on the flywheel side?

If the neighbor took out a root or a rock that sheared the blade hub key, they may also have sheared the flywheel key as well. T

This could account for the backfire situation. The ignition would be out of time with the rest of the internals.

shamu62's Avatar

Join Date: Jun 2006
Posts: 3

06-03-06, 09:31 PM   #4  
it was the flywheel key

I found the flywheel key shaved and replaced it. I thought I had found it fixed, but apparently, there's still something wrong.

Jerbear's Avatar

Join Date: Aug 2005
Posts: 43

06-03-06, 11:08 PM   #5  
You should not try to start a mower without the blade on it. The blade acts as a heavy flywheel which is needed to keep it from backfiring. Replace the blade and see if that helps. Jerbear.

cheese's Avatar
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Join Date: Jul 2001
Posts: 16,571

06-06-06, 01:59 AM   #6  
Correct, put a blade on it and it'll spin like it should. Check the crank though, there's a good chance it's bent. If so, it's probably not worth the expense of a blade and adapter hub.

"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

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