Let's Discuss: Leopard, PRD and Rotax Gearing for FK2 and Clubman Classes

With the addition of restricted 125cc Leopard, PRD, and Rotax engines to the certain F100 classes, F100 has opened the door for many racers who are new to the sport to enjoy F100 competition without the need to buy new equipment. Many racers have purchased restrictors for their Leopard, PRD and Rotax engines in order to race in one of these classes and F100 is excited to welcome these racers to F100 competition in 2017. 

Some of these racers have wondered about the gearing they should run with this restrictor. There is no maximum gear size in the FK2 and Clubman classes for the Restricted 125cc engines.

FOR FK2 - A good rule of thumb for the FK2 and Clubman classes is to add 4 or 5 teeth to the maximum gear sizes that were used in the former FK125 Masters class, listed below:

§  Adams – 82

§  Apex – 80

§  Bluemax Kart Track - 82

§  Buttonwillow – 82

§  Calspeed – 82

§  Grange CW – 80

§  Grange CCW – 82

§  Willow Springs – 84

Adding 4 or 5 teeth to these maximum gear sizes should get you in the ballpark. This means that for Grange CW you should start with an 11/84 or 11/85 gearing; for Adams you should start with an 11/86 or 11/87; etc.

Please note, this gearing rule of thumb may not apply for the Restricted Spec PRD engine package.

A quick note about carburetors - you may need to run the carburetor a little leaner with the restrictor. You're best bet is to check your spark plug to see how the engine is running and/or to speak with an engine builder to ensure that your carb and engine are running right and are properly tuned. For FK2 class racing running your engine rich is not the worst thing but you may be able to achieve a bit more performance with some attention to your carburetor tuning.