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While cranking over to start this Kawasaki FH680V 23 hp, it lets out a big bang thru the exhaust. On cold start, I use about 1/3 throttle and full choke. After about 8 revolutions, it lets out this big bang from the exhaust ,then starts up in another revolution or 2. Once it is running, it runs great. I don't know if it will hurt itself doing this, but it does scare women,children and livestock. Thank you for any suggestions on fixing my big bang. gregjo1948

What happens if you go full choke, full throttle?

Try it and see what happens.

I tried it at all differant throttle settings and the result is the same. gregjo1948

Has it just started doing this? have you tried new sparkplugs? fresh fuel?

I just put this engine together but, the previous owner said it was starting this way. It seems like it is pulling its fuel in and delaying the spark, causing too much fuel in the cylinders before igniting. I've cranked it over with the plugs out and grounded. It has an immediate strong spark. I've set the air gap at the coils to .005

Even though that is within recommended tolerance, does it change the spark timing if the gap is closer or wider? Once it's running, it runs very nice. gregjo1948

The air gap dose change the timing as I understand but not by much. I would say try it around .012 or so and try it. Could the engine be getting too much fuel? Maybe check the float level?

The bang is from excess unburnt fuel/vapor in the muffler finally exploding. Just try this to see what changes. The next time with a cold engine, put on full throttle and no choke at all and crank for several seconds, If it starts, well, that means something.

If it doesn't then go to full choke while still cranking, and see if you still get the bang.