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Old 10-10-2012, 08:41 PM   #1
kellymac530 OP
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Joined: Feb 2010
Location: so. cal.
Oddometer: 1,052
stroke twin issue

I know this NOT a jet ski site but many of you are engine gurus no matter what it is. I am having NO success on any PWC sites and I can not figure this out.

First off, I am a decent mechanic, not a pro trained tech, but the guy who everyone of my buddies call to figure something engine out. I have a full shop in my garage, bike lift, 6 hp 60 gal Air Comp, air tools, presses, pullers, TIG 250 Lincoln welder....you get the point. I am a do it myselfer and have built many cars and bikes and boats from the chassis up. No way near bragging here but just letting youknow that I am not a carpet salesman playing with tools, I work with my hands daily and am somewhat capable.

That said I am stumped big time. I have raced Jet Skiis and built quite a few of my own and A buddy had me rebuild his Sea Doo a couple years ago and it ran better than ever, new crank, bore, piston & ring kit...yada yada. So another friend asked to trade me a beat up tired BMW R80GS for my labor and parts to rebuild his 550 Jet Ski. No problem. I find out it does run but not well and it dies after running for a few minutes and wont start for an hour or so.

I take the deal. After stripping it down I find a worn thru spot in the water box, I assume that is the stalling problem since that is a common issue. I order a rebuilt crank, gasket kit, oversize piston N ring kit {after having the bores checked to see what size I need} and have the barrels bored, all from a reputable Jet Ski racing supplier. I clean everything carefully, and rebuild it all. Jet Ski engines could not be easier, crankcase splits down the center, crank drops in with a seal on each end and drop the barrels over bthe pistons.

A few hours and it is together it pops right off but wont rev up. It has good reasonably even compression {105 and 108} for an unbroken in 2 stroke. It has GREAT spark, brite blue even in a well lit shop from both plugs. I know the carb works because it was on a running ski before, and I have since rebuilt it just to rule it out and put a carb off of a third running ski on it. I also have lightly sprayed fuel from a spray bottle while cranking and it does not help.

It fires after 30-40 seconds of cranking, it will run with the throttle wide open but will not really rev up. I have since swapped out the entire CDI box from his other good running ski as well as the front magnetto and pick ups and flywheel all to NO avail.

What is wrong?

I have ALWAYS been successful with the concept of, if it has compression, fuel and spark in the right time all motors can run. It has never failed me. This is the first time I have not been successfull with a motor once I deduce down those simple points. I have tried timing it full advance and full retarded and at every notch in between which only about 15* or so total so I am sure it is not just timing.

Could there be something wrong with the crank that was a rebuild? The seal in the center not right?

ANY ideas will be tested and retest if you have an idea PLEASE throw it up. I am out of things to try here.
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