Rotax evo bogging

Hello all,

Running Rotax evo sr had a previous issue on top end RPM, turns out the tubing to the solenoid was wrong. Everything ran great after but now seem like it boggs a lot out of the slow corners. Any recommendations?

Thank you

Sounds goofy but check your accel cable rigging. I remember similar when I had rotax, it was the accelerator cable had slipped so was opening the butterfly fully.

Otherwise I dunno, carb cleaning maybe?

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Does that mean where the accel cable goes into the carb?

I’ve cleaned out the main jet but good point I’ll take apart the complete carb and clean it out. Thank you

No I mean at the pedal.

Just take off the intake box, press the pedal fully and make sure the butterfly (actually it’s a slider on Rotax I think) is opening fully.

When I was struggling the loop connecting the cable to the pedal had slipped, so at full gas the throttle was only 3/4 open. Not so noticeable after the power valve opened but awful up to it


You’ll find a configuration something like this at the pedal



never considered looking at that. That’s a good one, I’ll check it out. Thank you

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I checked the carb and it fully opens. Noticed the exhaust has a fairly large hole on the bottom because it was bouncing off the mount bolt. A fair amount of exhaust leaking out. I wonder if this could be part of the issue. Any insights?

It’s possible. The exhaust is supposed to provide a back pressure to stop the fresh fuel/air mix leaving through the exhaust during the initial phase of piston upstroke, whilst the exhaust port is still open.

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Take your pick:

Improper jetting. Try with the choke on. If the bogging gets worse, the main jet is too large. If it improves, you were too lean. Also look at you plug.

The clip on the needle is set wrong.

Improper float height

The RAV valve is sticking

The exhaust packing needs to be changed.

Fuel pump needs to be rebuilt.

The pre-EVO engines would bog out of turns if the accelerator was pressed too quickly. Think the EVO fixed that.

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Or just accept ‘because it’s Rotax’ n ditch it for x30 :crazy_face:


wow thank you, I’ll check all of these.

Haha my series is Rotax so no choice :slight_smile:

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Hey now, both products have their place…

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I know man, just larking around :grin:

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I prefer the throaty sound of the x30. Rotax is great but it doesn’t sound special. Ideally I’d have both.

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to give an update…

Tried a 122, 125, and 128 jet
Tried p1, p3, and p5 on the carb needle
Replaced the exhaust packing
Tried another racers PV
Tried another racers carb
Welded the hole on the exhaust
but still have the bogging out of the slow corners…

The only thing I didn’t try was float level and rebuild of the fuel pump.

The track owner said it could be the crank gasket. Not sure I understand how a gasket would cause this…

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An air leak into the crank can make it run poorly. It could be leaking at the base gasket, crank seals or crank half’s.

ok this will be the next things I check

You could try doing a pressure (or vacuum) test. Intake and exhaust blocked. Piston at BTC and see if it holds pressure or vacuum. For pressure it should hold 5-6 PSI for 10-15 mins. Vacuum, I’m not sure if a number.

Couple of other things worth checking.

  1. Check the reed block and petals. Hold it up to the light and you shouldn’t see any gaps. Also check the reed stops haven’t been bent.
  2. Perform a compression test. It should be somewhere around 150psi but every tester is different. Best to compare to a known good engine. Note that testers with the flexible hose are generally not very accurate.

didn’t think about the reed valve. Thank you so much I’ll check these out