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My Yardman backfires when I turn the key off. Is this due to valves being out of adjustment?

Do you shut it off @ full throttle or lowered rpms?

And is this something new to your machine ?

What year.
Mst newer ones have a solenoid on the carb which is very expensive to replace.
So a lot of people cut the plunger off.
Without a properly functioning solenoid the engine will backfire through the exhaust once to fuel & air gets to the correct ratio to burn at atmospheric pressure

7394 said:

Do you shut it off @ full throttle or lowered rpms?

And is this something new to your machine ?

Click to expand...

Yes, I have been shutting off at full throttle. I do not know if this is new to my machine, as I just recently got the mower. It had set up for a while. I've checked the spark plug and it was fine. I've cleaned the rust off the magnet on the flywheel and the coil. When I put the coil back on I used an old debit card to set my gap. Would that be too large of a gap? I usually just use a thin piece of cardboard.

bertsmobile1 said:

What year.
Mst newer ones have a solenoid on the carb which is very expensive to replace.
So a lot of people cut the plunger off.
Without a properly functioning solenoid the engine will backfire through the exhaust once to fuel & air gets to the correct ratio to burn at atmospheric pressure

Click to expand...

It's a 2007. The cut off solenoid is attached.

Mrbill1 said:

Yes, I have been shutting off at full throttle. I do not know if this is new to my machine, as I just recently got the mower. It had set up for a while. I've checked the spark plug and it was fine. I've cleaned the rust off the magnet on the flywheel and the coil. When I put the coil back on I used an old debit card to set my gap. Would that be too large of a gap? I usually just use a thin piece of cardboard.

Click to expand...

Understood, & that gap should be close enough.

You could test the carb solenoid just by turning the key on, (not starting it) just listening for an audible click. & turn off key & listen for same.

I have had 3 mowers with the Briggs SINGLE cylinder OHV engines, 2 were the 17.5 HP models, & 1 was a 15.5 HP, both 17s will ALMOST ALWAYS backfire on shut-down regardless of throttle position (fast or idle) it has so far never caused an issue other than scarin the hell out of the animals close-by, the 15 HP, never did it..after nosing around with some other mower owners at the mower store, we came to the conclusion the 17s short pipe BEFORE entering the muffler, was the problem, the "entry" pipe on engines with the muffler located LOW on the frame did not backfire, one fella said he fooled around, changing mufflers to find out for sure, he said installing the mufflers, back n forth proved his theory was true, I have not done this myself, I no longer had the 15 HP, ... anyway, I go along with his assertion, it's the length of the pipe,.. PRE-MUFFLER ! ( see pics of muffler setups )

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Thanks for the input. I guess the backfiring isn't anything critical and I can put up with it. I've noticed it sometimes will backfire when I start it also. The mower had set up a while and the carb and solenoid was all corroded badly. Perhaps the solenoid is sticking some.

Mrbill1 said:

Thanks for the input. I guess the backfiring isn't anything critical and I can put up with it. I've noticed it sometimes will backfire when I start it also. The mower had set up a while and the carb and solenoid was all corroded badly. Perhaps the solenoid is sticking some.

Click to expand...

If you're not hearing it clicking, then it's sticking. Try & turn on key (Don't start it, just listen near carb for the "click" then turn off key & should also hear a click @ carb.