650 SJ running wierd intermittenly...

[mxr181]

hey guys I am still pretty new on the forum...anyway I picked up a pretty nice 650SJ with a fresh motor, coffmans pipe, 175-180psi on both sides etc. Anyway the last few times out the ski sometimes will run perfect and sometimes it will run wierd...kinda like it is loaded up & or hitting a false rev limiter everytime you pin it, even when you go from a start. It feels kinda like it is surging, BUT if you are easy on the throttle and use less than half throttle it runs like it should and you can cruise around on plane UNTIL you pin it again. I have already put new plugs in, I think the gas should be clean, but I am going to get rid of the stock fuel filter and put an in-lne filter in, and clean the carb. The wierdest part is a couple of times it ran good for a few mins, then started doing the above for a little while, and then started running good again, almost like it cleared itself out from running too rich, but the plugs always look really good. Please let m know if you guys have any ideas! THANKS

[Danceswithsuperjet]

Make sure when you clean the carb to clean out the fuel screen on the fuel pump side of the carb. Those are usually a bigger problem than dirty carbs.
It's worth doing, but my gut says it's not your problem.

Could it be dropping to one cylinder?? Pull the boots off the plug wires, cut them back a good 1/2" and put the boots back on.

Don't have a lot of other ideas without riding it.

[mxr181]

thanks for the reply...I think anything is possible (especially after having a 550 that never ran!) Both of the plugs look pretty good though, if it was dropping to one cylinder would that plug be black from not burning everything? I went through the entire carb on both sides and cleaned everything...I lost the spring for the needle and seat but I had a spare so I used it...just not sure if its the same weight spring (they were both silver - not sure if that means they are the same or not). I also installed an inline fuel filter right before the carb so that I dont get anymore stuff in the carb. I didnt see a fuel filter so I am guessing that they are in the tank on the pick-ups? and the last thing is that the big filter on the left side of the hull up by the tank...was dirty so I took it off and it ran the without it on there...is this a fuel / water separator? not sure how stuff gets through it as the line goes to a vent on the top of the tank and another up into the handle pole...is this correct?

[mxr181]

Also after I put it all back together it sounds much better dry starting it in the garage...it revs all the way out cleanly like it used to so hopefully it was just a dirty carb...cant wait to put it back it the water! Trying to go this afternoon.

[daewootech]

i had a similar prob, definitly have the carb cleaned and tuned. itll do worlds of wonder.