booster

Like new RC390 booster plug. Fits all years. Comes with everything, including original box, instructions... I even saved the key chain. Only used for about 200 miles. I’m switching to a standalone ecu for my race setup so I no longer plan to use this. $120 shipped.

The surging on my RC390 seemed to be getting worse so I decided to try a booster plug. It arrived with instructions that were vague (as far as I am concerned, I am very familiar with jet skis but don't have a lot of experience working on motorcycles). #1 on the install instruction sheet says...