Keith – the significant changes are clutch, airbox, and a tightening of cylinder head castings tolerences (some pre-2009 cylinder heads are now illegal for official RMC events).  These are the basic things that will need to be changed/checked for RMC entry.  The clutch and airbox are no-brainers; the older clutch had reliabilty issues and the new airbox makes removal (for jetting) much easier.  The cylinder is something to check your casting number against the rules.  Do a search on Rotax cylinder casting and you’ll find the casting numbers that are legal.

Changes Rotax makes to the engines over time are designed to not improve performance.  Instead, the focus is on better performance consistancy between engines, improved reliability, and easier maintinance.

Other changes made are (optional*) hotter ignition module for more consistant high RPM performance, needle bearing and o-ring for clutch to prevent bearing grease from getting onto the clutch drum, improved battery options, and most recently, the reduction of carb venturi options from two to one (8.5).

* EDIT: Since this thread has been getting some traction recently, I wanted to clarify something I wrote to avoid confusion.  When I say the hotter ignition module is “optional”, that means the newer 2009+ coil with the green tab is NOT a required upgrade.  All newer engines have this coil, but it is not required to upgrade an older engine for RMC legality.

Keith with standing starts in Road racing. An old style clutch doesnt have a chance to the new style at getting off the line. You may have the same top speed. But by that time Im 10 seconds ahead of you at the start.

The guys that are in back of pack with a Rotax engine in CES events have older engines with no updates. Just my honest opinion.

Not sure where Jeff is getting his information from, but the old style clutch is/was governed by the same rule as the new style clutch.  It has to engage before 3000 RPM.  There is no ‘performance’ gain with the new style clutch, just better reliability.  Jetting and throttle modulation are the keys to getting a good ‘standing start’.

Nick Im getting my info from my starts and leaving most every old style clutch dusted. I tried racing old style everything and got my ass handed to me. Got old real quick when by the first turn at Blackhawk and other road tracks. That all the new Rotax engines are a 100 yards ahead of me and the rest of us that were on old style.

Nick that old shit still sells on ebay…..

There is a difference between the old style and new style clutch.  The new style is much better at standing starts. No question. But when I ran the old style clutch I was never left in the dust as Jeff say’s. But I knew of ways to make it get off the line better.

My engine is an 05 or so with the only updates being the Airbox and clutch and I’m able to run up front in CES.  But I have noticed some guys got FAST the last year or so by going with a new package.

Just get the new style clutch and airbox and you should be fine.  Getting a bad start really hurts in road racing.  I’ve had a few of them this year and losing the lead draft right off the bat really hurts. The Rotax is finicky.  If you don’t have everything just right your going to be a little slower.  I only race about 3 times a summer and if I don’t have everything just right I’ll be about a second off.  The more you race the easier it is to get things just right.

Too bad we don’t live closer to each other, I could show you…  Your great starts are a testament to your jetting and throttle control.  If you don’t want to take credit for it, then don’t.  At our club here in the SouthEast, I’ve seen guys with old clutches smoke everyone and I’ve seen guys with new clutches smoke everyone.  I’ve only been road-racing them for about 12 years, so I could be wrong.

On another note…  The original poster never once mentioned Road Racing that I can see.  You fellas must know him personally?

Ok so if I’m looking at a Rotax kart how do I tell the difference between an old and new style clutch? Thanks

The older clutch drum is larger in diameter and has six sizable holes in the front side.  The 09 and newer clutch is smaller and has a solid drum.

Inside, the actual old clutch has many parts including shoes, springs, support bracket, etc.  The 09 and newer clutch is a single machined peice.

!!!