I purchase a 2011 sea Doo challenger last year. Ran great, winterized it. At first sea Doo would not go over 6000 rpm. And sputtered at lower rpm. Though maybe I did not add the right amount of fuel additive. Added some new fuel, now still does not go over 6000 rpm, except will sometime surge to 7000 rpm. Close to what I remember at full throttle. Could this be degraded fuel? Is there a recommended fuel additive?