Backfire

Backfires are commonly related to the valves not seating properly or timing issues. Check that the valves are properly adjusted and look for anything obvious while you're in there.

Had an old lawnmower that would do that too. Turned out to be the carburetor had an electronic valve (solenoid) that would close when the engine was shut off. It started acting up and when the engine was shut off the fumes would get sucked in and BANG! The fumes would ignite just from the heat in the exhaust manifold.
 
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Rance said:
What Derrel said and what Ted agreed with. Fuel solenoid maybe bad.
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^^What Derrel said and what Ted and Rance agreed with. Fuel solenoid maybe bad.
 
Dang...not to hijack my own thread but this site really ranks fast. I was searching fuel solenoids not a hour after posting this and came across this thread on the world wide interwebs!
 
Pat Norman said:
Dang...not to hijack my own thread but this site really ranks fast. I was searching fuel solenoids not a hour after posting this and came across this thread on the world wide interwebs!
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Pat, that's why it's great to blog here. I need to do it a lot more.
 
Pat Norman said:
Hey Russ do you have the fuel solenoid for a gx670?
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What Derrel, Rance, Chad, and Ted said...

What happens is this. When you shut the key off, you kill the ignition. As the engine slows to a stop, it's still breathing air and fuel (thus the solenoid) in and out of the cylinders. Once the engine comes to a stop, you have a cylinder with a nice charge of fuel / air. The exhaust valve is still extremely hot, and causes the mixture in the cylinder to flash, causing the backfire.

Yes' Pat, I can get the solenoids. $36.19 plus shipping from Nashville, TN.
 
Russ Johnson said:
What Derrel, Rance, Chad, and Ted said...

What happens is this. When you shut the key off, you kill the ignition. As the engine slows to a stop, it's still breathing air and fuel (thus the solenoid) in and out of the cylinders. Once the engine comes to a stop, you have a cylinder with a nice charge of fuel / air. The exhaust valve is still extremely hot, and causes the mixture in the cylinder to flash, causing the backfire.

Yes' Pat, I can get the solenoids. $36.19 plus shipping from Nashville, TN.
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BINGO !!! I knew Derrel was right and Ted agreeing with Derrel was also right. Chad too!
 
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