96 XP ignition cutting out, backfiring

[sbklf]

Starts and idles fine but on acceleration cuts out spits, backfires. Let off the throttle and it goes back to idling fine. With an inductive timing light I can see both cylinders firing fine at idle but cutting out on acceleration. Seems if you baby it you can get it to accelerate a little past idle but misses and runs bad. I have gone thru the fuel system and am sure it is fine (carbs, lines, selector). I feel the timing light test points to ignition. I have a manual coming but hope someone here can give me a clue or an idea what to try.

 

[dsw222]

whats the compression on each cylinder?

 

[sbklf]

118 and 125 but I did not check it with the throttle wide open if that makes a difference.

 

[pthompson7]

Shouldn't Make a Difference

Having the throttle wide open shouldn't make a difference, since there are no spark plugs in it and the ski isn't running, your just cranking the engine over to get the compression rate for the cylinders. Did you let it crank a few times to get the highest PSI that it would put out. If you just let it crank over one time, that won't be the best compression rate you can get.I cranked it until the guage stopped going up.

 

[sbklf]

I am running my Yamaha with low compression and other than starting hard and probably lacking power it runs fine. Unless there is something about these Rotax motors I don't know about, I don't see how low compression could cause it to run bad like it does.