632 Bacfires on shut down

[DMZ1965]

I am working on a 1979 Bobcat 632 for a friend, got it all tuned up and it runs fine but when it is shut down it backfires once upon the engine stopping completely; the owner says it has done it for years. I have little experience with these machines so if anyone could shed some light on this I would appreciate it.

 

[jerry]

If there is a electrical solenoid on the bowl of the carbureutor check it. It should shut off fuel flow when the switch is turned off. I would more suspect advanced timing or carbon buildup in the engine which is getting hot enough to detonate last fumes .

 

[Tigerhaze]

I have a Model 610 that does the same thing. As previously mentioned it is likely a minor carb/ignition adjustment issue but not something you should get overly worried about.

 

[DMZ1965]

I have a Model 610 that does the same thing. As previously mentioned it is likely a minor carb/ignition adjustment issue but not something you should get overly worried about.

Thanks for the info, I will check it out this weekend.

 

[OldMachinist]

Thanks for the info, I will check it out this weekend.

You may need to find a shut down procedure that prevents the backfiring. Like letting it idle for some time period before shutting down. Other tricks would be if it has a manual choke, pull the choke right before turning the key or it may be opening the throttle fully before turning the key. I have old Ford tractor that likes to backfire on shut down but if I pull the choke it doesn't do it. My zero turn lawn mower just needs a short idle time and it doesn't do it.