Rotax stumble: is this it?

I’ve heard from pals that you have to be a bit careful with rotax off the bottom end. It doesn’t seem to like it when you step vigorously on the gas coming out of low speed corners. One needs to “roll into” the throttle carefully.

Here’s when I encounter what they must be describing. You can see that I go to gas and the engine seems to stick at a certain rev. By blipping the throttle, it seems to clear and you start building revs again.

Does anyone know exactly what’s going on here, mechanically? Some sort of deliberate reason for this choice?

Any thoughts from rotaxists on how to drive em given this peccadillo?

It has always been said that the carb on the Rotax is too big leading to the ’ bog ’ you describe.The evo setup supposedly improves things as did a tillotson conversion. I think you are meant to allow for the delay by getting on the the throttle earlier but that was beyond me in the short time I had one.


Once I experienced it, I found it manageable, actually. You have to be more “squirty”. It also forces you to be more aware of the general idea of being flat only when wheels straight, bringing throttle in as turn unwinds kinda thing. No Hulk smash.

Be smoother, don’t get held up behind other guys, and roll onto the throttle more progressively. About all you can do. Part of the reason I find Rotax to be rather unpleasant to drive.


The carb might be too rich on the bottom, blipping the throttle might be adding air to lean up the mixture. Setting up the carb at least in the earlier Rotax motors was key but I’m not at all familiar with the Gen 2.

I used to roll on the throttle, sort of imagining staying just ahead of the power curve.

A well set up kart that rolls, doesn’t push, oversteer or slide combined with good smooth driving seems to reward the Rotax more than other motors.

We used to run Mojos they were the worst tires, one lock up or slide and they would hot and the side bite would go away (felt greasy) and it would slow down a 2 or 3 tenths. This was only remedied by cooling the tires off by slowing down a bit.

Gear it tall if you can (track layout may not affect this) because it has tremendous mid-range but the chassis, driver and carb all have to be right. The short point and squirt tracks are not suitable for a Rotax.

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Yeah, once past a certain rpm it really has nice midrange and pulls. I found that it kind of wants you to treat it like a momentum kart a bit, kinda like a regular low power 4-stroke. You gotta catch the load with the throttle at the right time, wheels gotta be pointing straight or you need to trickle it in as it unwinds.

That’s funny my son said exactly that last week after his first ever drive in a proper kart. He said dad it just bogs down when I give it gas out of the low speed corners. I told him don’t mash the throttle and try to keep you corner speed up :man_shrugging:
He still had a blast though and was amped up for a day or so after. Think I’ve got him hooked:)

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