Hello, i'm new here and joined to see if I could get some help getting my 1990 js 550 running. The story behind it goes like this.....About 10 years ago I replaced the rings and it has not run well after that...So I just dusted it off and am currently trying to get it going I drained the fule and put new fule and it starts up and runs rough spittering and sputtering with a backfire here and there it seems to run fine at higher rpm's but down low it runs bad with poor throttle response but will jump to the hirger rpms and seem to be fine ....I'm lost. I checked the compression on both cylinders both good. I would love any help!! Thanks!!

 

If it has been sitting that long i would most definately be giving your carbs a clean out or maybe even an overhaul. For it to be starting and teh compression to be ok thats a good start..

you can pick up carb rebuild kits for these no problem at a reasonable cost.

 

So i had a buddy come over and "tune the carb" we got it running perfect on the stand hooked to a hose....so we took it to the lake to ride and to both of suprise it seemed to be running perfect but when you got on it and tryed to ride it just woulden't go bogging and very low on power so I tried to pump the primer and it would run alot better while pumping,so it seems pretty clear the it's a fule problem, am I right??

 

Sounds like it to me, the problem with the hose is you cant simulate a load in the garage so you never know how it will really run until it hits the water. I would go back through the carb and make sure everything was put back together properly (its easy to make a mistake) and also check your jetting. If the carb checks out, check the fuel filter and fuel pressure, then you may have to move on to ignition but I'm thinking the fuel will cover it.

 

Well I went through the carb again with the shop manual,cleaned everything,checked that it was put back together right , again it runs perfect on the stand but once it gets to lake it feels great when your standing there like it wants to go but when you get on and go it won't ,just part throttle and that's all it will do.....Any help??

 

The fuel requirements with a load and without a load are different, you may have to "tune the carb" in the water. Hope it helps, really sucks if the lake is a long trip.