Modded 580 needs a little tuning advice

[IDoSeaDoo]

I recently put a new top end and rebuilt the carb with new Mikuni kit on my 92 GTS: Stock bore, single carb, stock R/V, 145psi on both cyls, 2.0N/S, WestCOast pipe, K&N Flame arrestor, and old Solas prop (dunno what pitch, it's chrome plated and was bought in the early 90's). I've gone up two sizes in my jets (72.5 main and whatever the 2nd size up from stock is on the High (127.5 I think)). I'm still having issues in the mid-range. It idles great, and tops out well, and doesn't seem to have much hesitation from idle to WOT, but if you hold it in the middle, it surges, and feels like it wants to run stronger, but can't. It's as if it's a really steep transition point, because if you open the throttle to 75%, it runs great. If you turn at that 50% throttle, it loses power and slows down considerably. I'm not sure if it's rich or lean. I ran it like that for about a minute and the electrode looks pretty dark, like black coffee with just a touch of cream. The insulator is pretty brown too. Can it possibly want even bigger jets, or do I have some other issue?

Another thing to note is that between 75% and 100% open throttle, there is VERY little difference in RPM and speed.

Help would be GREATLY appreciated, THANKS!!!!

[Technical Support]

Re: Modded 580 needs a little tuning advice

It could be too rich, turn the low speed screw in 1/4 turn, see how it acts, if it is worse dont continue riding go the other way and turn it out till the problem gets better, if you have to turn it out past 2 turns then move up 5 jet sizes and turn the screw back into 1 turn out and test from there.