rotax max no low end power HELP??

[kris kobat]

hey guys im new to karting, (but not new to 2 stokes or rotax)and recently picked up a used birel rx32 chassis with a rotax junior along with a buddy and my father, here is the problem compared to the other which are all rotax engines mine has zero off idle performance i mean ZERO the kart doesnt really seem to pickup and go till almost 4-5k rpm and even at idle it is notably different sounding almost 4 stroke sounding, so i decided over winter to pull the cylinder cover to see if something was messed up and the piston was cratered like the moon and cover was ruined as well. So i used this opportunity to do a top end rebuild with a new rotax SENIOR cylinder, new rotax evo piston, new clinder cover, set the squish within specs, upgraded to the complete evo kit, and low and behold after recommended break in, still ZERO bottom end power and still notably sound different almost like a 4 stroke chug. only thing different between karts is i have the old style clutch compared to thier new style clutches. but was informed there shouldnt be that big of difference, so i rebuilt the old style clutch with springs etc. still nothing. the kart is running on the rich side with the stock 130 jet but i wouldnt think it would make this much of a massive difference. any help or ideas will be much appreciated thanks guys.

[Samir Shah]

So, have you looked at gearing? If its set up for road racing instead of sprint racing, it might not have torque and might be too long. Also, check the axle, bearings, etc. It is binding? Can it spin freely? Is the brake rubbing or stuck? Is the drive sprocket attached to the axle, or is the keyway broken, allowing the sprocket to spin without moving the axle.

[kris kobat]

I’ve checked all that kart moves free it has a 13t front and a 79t so I don’t think it’s gearing it it’s just standing starts, once you are moving you can’t tell it’s just the off idle to mid performance, say up to 5k rpm then it takes off and pulls cleanly and hard

[Steve piggott]

you are chasing an unfixable issue, the rotax has zero pull right out of the gate. The class does rolling starts not standing starts like a shifter class so the engine power is middle to high rpm

[kris kobat]

I understand that but I mean it is such a huge difference from one rotax kart to the next I feel as if something isn’t right our other kart will literally spin the tires right off idle and mine doesn’t even want to try and go till about 5k and the other kart even has a 14t front gear just wanting to know if there is something I need to look for also I thought the rotax does a standing start

[Matt Clark]

Spin the tires off a standing start?!

[Steve piggott]

next id lower jet size by a few just to make sure and power valve is closed ?

[tony zambos]

On rolling starts and down the straight a ways, how does your kart compare? Are the other engines EVO? What rpm does your clutch stall at?
FYI- The new style clutches came out a few years ago. Along with the new clutch and drum came metal gears to replace the nylon ones. IMO you should have upgraded the clutch along with the EVO mods.

LAD Specialties customer / tony kart / rotax / kt100

[Rob Kozakowski]

First, no Rotax Max will spin the tires off a standing start or from a low speed.  They have nothing at low RPM.

Some people claim that the old style clutch is even worse from a dead stop than the new style.  Unless you’re road racing with a standing start, this shouldn’t matter.

Others claim no difference from a standing start between old and new style clutch.  Both clutches engage around 3000 rpm, so there shouldn’t be any real difference.  They say it’s all jetting and throttle application.  While I have no experience with the old style clutch, that is 100% the case with the new style – jetting and throttle application.

With the Dellorto carbs on the Rotax Max, you can’t just hammer the throttle.  You need to roll into it, or you will give it more fuel than the carb can handle at low RPM.  The new EVO carb is a little less sensitive to this.

If your problem is nothing below 4000-5000 rpm, it really shouldn’t matter. You should probably never be in that low of a range when racing the Rotax Max.  If you are in/below that range, work on gearing and/or work on your driving/chassis setup so that you aren’t scrubbing speed or bogging the engine down.

[Author]

Posts