High RPM "BOOST"

Timothy Breuer · Joined: 24 Jun 2002 Posts: 11 Location: South Florida

Yesterday while practicing, my Rotax would get up to about 11,000 RPMs a little sluggish and then at around 11,500-12,000 RPM's it would just take off noticeably like I hit a nitrous button or something. I backed off the “power valve” all the way and it made no difference.
Any suggestions?
Thank you

Shannon Schmidt · Posted: Tue Aug 20, 2002 8:17 pm Post subject: High RPM "BOOST"

If you look in your manual (if you got one!) there is a performance graph that shows the power curve of your motor. The Rotax engine has a steep curve until you reach 12,500 rpms. It then drops off until you reach 13,500 rpms, then it picks back up until you reach 14,000 rpms. So it sounds like your motor is doing just what is supposed to!

Shannon Schmidt · Posted: Tue Aug 20, 2002 8:24 pm Post subject: High RPM "BOOST"

Couple more things..if it is sluggish going up to 12,500, you may want to adjust the air mixture screw (turn it out a little at a time), or check your main jet. The power valve should only have a bearing on the point on the band where it opens up.

Perhaps someone else on here has a few other tricks...but that is what I would do.

Neal Wood · Posted: Wed Aug 21, 2002 11:53 am Post subject: High RPM "BOOST"

Once you get the jetting and gearing right it should be able to rev smoothly right through to 14k. It takes some testing time to get it figured out. Throttle modulation is also key to getting the best power. Not to fast on the gas, but not to slow either.

Neal

Blake Newson · Posted: Wed Aug 21, 2002 8:12 pm Post subject: High RPM "BOOST"

Tim: What you described sounds a lot like what I and the other guys I run with seem to experience. I agree with the comment that the Rotax power curve in the manual shows the drop at 12,500 and then a positive curve well into the 13's, but I (we) seem to notice the power pickup at roughly 12,700-12,800, which doesn't really match the curve in the manual. I think Neal made a good point about jetting and throttle control.
This engine is all about JETTING and fuel delivery!

Timothy Breuer · Joined: 24 Jun 2002 Posts: 11 Location: South Florida

Thanks for all the help...I think it's been solved. I was running a 162 jet when a 158 was more appropriate, my battery was a little low, and my power valve was loose. After changing these things, I'm flying.