briggs back firing

[plotthound]

my lawn tractor with an 18hp single briggs intek has started backfiring.usually only on start up when its warmed up and sometimes on shut down.would the fuel solenoid shut off cause this?gotta fix it before the the dog craps a brick.

[KE4AVB]

Depends...Is this the actual after fire problem out of the exhaust or is it out of the carburetor?

The after fire (often called a backfire) is raw fuel entering the hot exhaust and the after fire solenoid was added to carburetors to help prevent this. The raw fuel ignites in the exhaust due it being red hot internally.

The real backfire out of the carburetor can be caused by ignition timing usually. Something like partially sheared flywheel key. I ran one case where I had a 310000 series randomly sneezing out the carburetor. Not something that shot a flame out of the carburetor. This was an intake manifold air leak. On a Homelite I had a coil that did it so bad it was setting the air filter on fire.

I had Kawasaki engine igniters to misfire on at the top of the power stroke and then ignite the fuel on the exhaust stroke. One of the drawbacks of the wasted spark ignition system. A failing plug may fire under compression but fire fire on the exhaust stroke. The first one I came across I nearly wet my clothes as it was as loud as a 12 ga going out right beside me and that was with the muffler on the engine. It also shot out a twelve inch plus flame everytime it did it. I was nervous wreck the rest of the day.

[plotthound]

im positive that its backfiring out the exhaust.its more like an explosion.

[RoyM]

Raw fuel is being drawn into the muffler after the key is turned off and being ignited by the heat. The afterfire solenoid is supposed to prevent or at least minimize this. Have you tried idling the engine down for a minute or two before shutting it off? The idle speed might also be set too high.

[plotthound]

will try idling down for a few minutes before shut down the next time I cut the grass.thanks

[KE4AVB]

Another option provided you already have the fuel solenoid on the carburetor is to let it do the engine shut instead of killing to magneto. I have a few JD that I service that are setup that way from the factory. This way the fuel/air mix is burned off as the engine shuts down from the lack of fuel.

[plotthound]

Another option provided you already have the fuel solenoid on the carburetor is to let it do the engine shut instead of killing to magneto. I have a few JD that I service that are setup that way from the factory. This way the fuel/air mix is burned off as the engine shuts down from the lack of fuel.

how exactly do I do that? put a switch in the solenoid circuit? I tried idling down before shutdown but it still back fires if I restart it when engine is still hot.

[bgsengine]

backfire on restart sounds more like a loose valve seat or sticking valve.