It is hard to figure as they use rather weak magneto

ignition systems

Paul, and Perry I always ran 100LL in my yamaha FZR 1000 race
bike, at 10:1 compression and NEVER even hinted at fouling a plug.
This was running a total loss battery ign with crappy stock coils!
Point is Perry must have something in conflict with the lead or
perhaps your mixture isn't as lean as you think Perry. On my race
bikes the 100LL always left the exhaust a light tan unless

the mixture

was so rich it would barely run. Bill Jepson.

something about the combusion chamber flow patterns with

a 'port' type engine?

Ken Powell

Ken, Yamaha published jetting charts to use with aircraft

fuel including 100LL.

In fact they suggested running leaded race gas as well. At least as
late as '93-'94. The PREFERRED fuel was the ELF super zoomie
unleaded. The stuff ws so exotic that casually smelling the fumes
could hurt you!  Bill Jepson

Hi Bill,
My problem was that I ALWAYS jetted the midrange rich to cover the occasional (regular???) jetting screwup.  I mostly raced Hair Scrambles and Enduro's back East so an event would last 2 to 6 hours, so a fat midrange on an open class bike (and the weak ignitions of the day) could be troublesome with leaded gas.  I also wanted the mixture rich to help cooling (air cooled engines).  I always found the needle difficult to jet since changes were always made on the scene and with temp variances of maybe 40 degrees thru the course of the day - it was next to impossible to get a steady state load at 1/2 throttle on an open class bike.  Anyway, thanks for the explanations - someday I am going to finish a minimax 'near' ultralight and will use a Kawasaki snowmobile engine for power so I am still interested in the 2-stroke stuff.

Ken Powell

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