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Discussion Starter #1
Hi Guys,
I have a s21XXX f engine push mower that pops a few times when first cold started. It only does it maybe 5-10 times and then will not do it again. What causes this? The mower has real good power but seems like it gains rpm when warm also. Bad seals? I don't notice any leaking from the lower one but have not checked the upper. Thanks.

-Dave
 

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What I have seen with Lawnboys backfiring (if that's what you think it is) is ignition related. Had an older one that would start to rev up, back-fire, rev, back-fire, etc. Changed the coil (old one was cracked and beyond help) and i was off and running. If not the coil, maybe a bad plug or plug wire??

Keep us updated on what you find.
 

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Discussion Starter #4
I think Brad is on the right track. It's probably timing related in the CDI module.

Thanks. I'll try a different coil and see if that cures the problem.

-dave
 

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Discussion Starter #7
Or spark plug.

Walt Conner
Thanks, Walt. I will check into that one too. I don't know if the compression is low. It went through some very tall, thick wet grass with no problems.

-dave
 

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Lawnboy Green
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Hi Dave,
While you have the shroud off, look at the flywheel key to make sure it hasnt moved and advanced its timing a little.

Best wishes,
Bob
 
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