Engine strong from 8k-12.5k, weak low and high

Craig Drabik

Hello all. I had my first outings with a Rotax motor this last weekend and I was hoping some folks could point a new owner in the right direction. The engine is bogging coming out of the pits and weak out of a slow hairpin until around 8k. It noticably comes on song at that point and pulls well until around 12.5k. At that point, it just won't rev. I've changed gearing, eventually dropping 6 teeth, and only ever seeing between 12.6 and 13.1k, and more teeth didn't necessarily get me higher revs.

I decided to try a jet change, and based on what was happening I kind of thought leaning it out was the way to go.. I checked the chart for the temperature and pressure at the time it was between the 162 and 165. I was running the 162, so I tried the 165 even though it seemed wrong to me (though less likely to blow up the engine). It didn't help.

I ran it on Sunoco 110 with XPS at 40:1.

I'd love to hear everyone's thoughts.

Joe Ricard · Posted: Wed Jul 25, 2012 7:15 am Post subject:

I thought Rotax only requires 98 octane fuel. and recommends 50:1 per the manuals.

Look at the pipe and piston for jetting info.

My son's Mini max runs on 93 real gas quite well but squish is bigger on the Mini as opposed to a senior Max.
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Arrow AX-8/ Rotax Sr.

Steen Carstensen · Posted: Wed Jul 25, 2012 9:52 am Post subject:

Rotax is designed to run on regular pump gas, i.e. anything from 91 to 94. You can run whatever you please, but you are waisting your money.

Craig Drabik · Posted: Wed Jul 25, 2012 10:17 am Post subject:

I ran it on 110 because it was a spec fuel in this situation. The break-in was done on 93 octane pump gas and after break-in, I also had trouble breaking 12.5k on the 93. I don't think it was the fuel.

Nick Weil · Posted: Wed Jul 25, 2012 11:43 am Post subject:

Sounds like a little rich still on jetting, and perhaps your needle position is also rich.
_________________
Nick Weil
Authorized Rotax Service Center and Dealer since 2002
2004 Team USA Rotax Worlds Finals DD-2 Driver

Want to save money AND grow the economy? www.fairtax.org

Scott Falcone · Posted: Wed Jul 25, 2012 6:00 pm Post subject:

Check the following :

Carb:
1. Be sure the floats are installed correctly. On top of the float arms not underneath the float arms.
2. Be sure the needle and seat is screwed down all the way.
3. Be sure there isn't any fuel in the floats.
4. Clean the carb filter.
5. Pull out the pilot jets and clean.
6. Keep leaning out the main jet to see if the revs come up go to a 155 to see if that pulls them up. You will lean pop if its to lean, than just add a jet or two.
7. I wouldnt worry about blowing up the motor by being lean. The Rotax is very good motor and difficult to blow up especially with jetting.
8. Fuel mixture is fine.

Power Valve:
1. Be sure to that the power valve blade is not in upside down.
2. Be sure that the gasket between the blade and the housing isn't installed upside down. There is a little 1/8 hole on the gasket that needs to line up with the housing hole.
3. Check the length of the power valve. PM me for more info on that.

Pipe:
1. Check the packing may need to be replaced.
2. Double, triple check for cracks especially around the welds under the pipe.

Please email me if you have any questions I don't look everyday. Good luck.

Scott Falcone
S.F., Inc
303-210-5991 (w)
303-741-8656 (f)
www.sf-Inc.net
Scottfalcone@comcast.net

Craig Drabik · Posted: Thu Jul 26, 2012 9:05 am Post subject:

Thanks for all that great info Scott. I'll go through and check everything out.