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  #11  
Old 06-18-2012, 06:18 PM
Bashby Bashby is online now
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My older Kohler backfires when shut down at idle. It doesn't at full or half, If i let it idle then open the throttle as i shut the engine off it prevents the backfiring
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  #12  
Old 06-18-2012, 07:48 PM
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Ijustwantausername Ijustwantausername is offline
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Quote:
Originally Posted by hammmerhead View Post
It shouldnt backfire idled up or full throttle if it is running correctly. A LOT of the old Kohler engines were notorious for this. You wouldnt happen to have a Kohler would you?
Its a 31HP Kawasaki.
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Old 06-18-2012, 10:03 PM
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Idle it down.

Switch ignition off.

At that exact time give it throttle.

You won't increase RPM's by doing this and it will open the throttle blade(s) in the carb.

Or just buy an EFI. They don't do this.
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  #14  
Old 06-19-2012, 12:03 PM
VegetiveSteam VegetiveSteam is offline
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Quote:
Originally Posted by Ijustwantausername View Post
He said don't let it idle down then turn it off, rather he said turn if off after you've disengaged the blades at full throttle so the motor can spin down and prevent a backfire which he said has caused things to shoot through the motor, piston or whatever.

Any truth to this? It backfired twice today, once was my fault because I forgot to pull the brake up, so I had to do it real fast when I stood up, second was when I turned it off at idle, but the yard I mowed took probably 5 minutes.

The manual clearly says let the engine idle down before cutting it off and it also says engage blades at 3/4 throttle to prevent clutch wear, something the dealer told me to do at full throttle as well...


Do you know if it has a fuel shut off solenoid on the carb? Most do these days. If there is a fuel shut off solenoid on the carb, shut the engine off at full throttle. That should take care of the afterbang. The engine owner's manual it should have shut off instructions in it for both with and without fuel solenoid.

What the fuel solenoid does is shut off only the high speed circuit of the carb. If you shut the engine off at idle you are still pulling fuel through the idle circuit and that fuel thrown unburned into a hot muffler causes the afterbang.

When you shut the engine off at full throttle the fuel solenoid shuts off the high speed circuit of the carb but we are still able to pull fuel through the low speed circuit of the carb. This is where the governor comes into play. You have your engine running at full speed. With no load on the engine the throttle is bearly cracked open and the engine is still running mostly off the idle circuit. As soon as you turn off the key the engine starts slowing down. What does a governor do when an engine slows down below what the governor wants the engine to run at? It opens the throttle more. The governor will continue to open the throttle on the carb until it gets the engine back to the RPMs it should be running at. Will it ever get back up to speed? No. The engine is turned off but the governor keeps opening the throttle until it is open all the way. Now we are sucking in a lot of air. The main or high speed jet is closed because of the fuel shut off solenoid. We are still getting a little bit of fuel out of the low speed or idle jet but now there is so much air being pulled in because of the wide open throttle that most of the fuel just evaporates and what makes it to the hot muffler is way too lean to burn. Result? No more afterbang.
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