'05 sportster 155 hp surging

[JrSenior]

Hi, new to forum and Seadoo owner. I picked up an '05 Sportster 155 hp with 28 hrs total time. It seems to run fine except a bit of uneven idle, say 200 rpm changes, as if one cylinder was dropping a bit. I changed plugs and ran Valvteet additive for ethanol along with a tank of premium. The old gas was pumped out to about 5 gal left in the tank. Probably 18 months old in a hot climate. I'm showing 48 mph on the GPS at WOT, 73-7400 rpm. Is this normal? Thanks in advance for experienced advice.

 

[thor7000]

Congrats on the new boat!! Your speed sounds about right, as far as your rough idle....does it happen all the time or just once and awhile??

If you don't mind me asking, how much did you get your sportster for??

 

[JrSenior]

Rough idle is all the time. Paid $7500 w/trailer. Mostly looks new.

 

[Bills86e]

You should not have left 5 gal. Gas goes thru a chemical change after it ages, usually 3-6 weeks, and is non-reverseable. Stabil can prolong to 6-9 months, AND
has a lubricating effect, and helps moisture thru the system.
Surging could be throttle body. inspect the #13 0-ring and manifold gasket for air leak.
http://fiche.worldofpowersports.com/wps/Seadoo_OEM/Seadoo_JB.asp?Type=13&A=110&B=7