Back firing through carbs

[jjsearay]

I just had a guy bring me a 1995 sea doo spi with new 587 sbt motor that he installed. All he could get the motor to do is back fire through exhaust and carbs. I pulled the rotary valve and checked for 147 timing and it was dead nuts. Put new plugs in and cut back wires 1/4 inch. Motor threw a rod prior to new installation. Any chance that when he pulled the pto back on that the flywheel slipped a bit. I wanted to ask if this would throw the timing off before I start ripping the motor apart? I did not know if the timing would be affected or not by it slipping. I know on the larger motors it does. Please advise. Thanks

[tjcz71]

Re: Back firing through carbs

Im not quite sure what you are asking here.... the pto is threaded on.... its possible that he over-torqued the flywheel nut and sheared the key. Did he rebuild carbs? He may of put a gasket/diaphram in the wrong place.

[dsolie]

Re: Back firing through carbs

Did he install the stator in correctly??

[Bill O'Neal2]

Re: Back firing through carbs

I'm guessing he either mistimed the flywheel by losing the key in the nose of the crankshaft, or he used the wrong magneto flywheel with the wrong stator when he rebuilt it. You do know that you cannot mismatch flywheels with the wrong type stators, right ?
Backfiring is usually an ignition timing problem if the RV is set correctly.

[Bill O'Neal2]

Re: Back firing through carbs

Did he install the pistons backwards ?

[jjsearay]

Re: Back firing through carbs

Thanks Bill for the help, but I found that the woodruff key had sheared off causing the timing to be off. When he pulled the pto on he held back with the fly wheel and unnoticeably sheared it off. Put a new woodruff key in and it fired right up. THanks

[Bill O'Neal2]

Re: Back firing through carbs

That is why I remove the head, place a block of wood on top of the piston, replace the head, then remove a stubborn pto flywheel. No strain on the woodruff key.