Motor backfires Kawaski FH601V engine on lawn mower will start backfiring after a few minutes of running. Have cleaned fuel tanks, fuel lines, then replaced fuel lines and clamps, fuel filters, cleaned and rebuilt carb, replaced fuel pump with a new one, then replaced fuel pump with elec pump, checked all wiring including ignition switch and problem continues. Runs when first started then when blades are engaged motor begins to backfire constantly and will not stop even if blade are dis-engaged.

only thing left is valve seat is loose and poping loose at a certain rpm causing backfire threw carb has to be intake valve

unusual, would normally say air filter but thats new. theres no restriction on fuel is there from fuel tap. so it runs out and slowly fills, time you check its got fuel again. is there a breather into tank blockedi has it once on a bike that used exhaust paste. the person had put too much in and it blocked the exhaust.

clean the jets inside the carb

Backfiring and running rich? It sounds more like the engine is running lean. Your problem sounds like a fuel problem rather than an ignition issue. However, did you by any chance strike a rock or something solid while mowing? The reason I ask is because you replaced the flywheel key. Another possibility is that the crankshaft has been bent and that could also cause the problem you are describing.

It's called "hunting" and its caused by the engine running too lean. It needs the carby and fuel system cleaning out. Also the fuel shut off solenoid in the bottom of the carby needs checking for proper function. Regards Phil

Had the same problem with an almost new Craftsman w/ Intek 20.0 HP. Check all the "usual suspects" and had to have a tech come out. He had me start it. It ran for a few minutes and stopped (per usual). He immediately went to the Anti-Backfire solenoid. It is an electrically operated "plunger-style" fuel line blocker. They are famous for going bad. The part is about $65 and its sole purpose is to starve the engine of its fuel supply at shutdown so it won't backfire. If it is disabled, the user must throttle the engine down for 10 seconds or so before turning the key off in order to avoid backfires. Gee... let's see, 10 seconds of my time each time I use the mower vs $65 part ... No contest! Remove the solenoid, take a pair of electrician side cutters and snip off the tip of the plunger and reinstall it. Problem solved ! ! !

be more specific make sure your motor has an exhaust the motor should be sucking in fuel and you might want to rev the motor as soon as you start it

check fuel pump diaphram is not streched or hard, check fuel filter for blockage, or fuel tank cap might be not venting, if none work drain and clean out carby bowl.

Most likely water in the fuel. Drain the tank and clean the carb. replace with fresh gas. Mr fix it is a dumby