100cc Air Cooled Techniques

Think this is the right forum for this…

Curious if anyone wants to share advice/techniques on how to maximize engine such as the KA100/VLR100 beyond just putting your right foot to the floor. In passing, sometime I hear of the ICA Days where people would tune via airbox manipulation (noting illegal) by covering air box intake into turn one, or by “slapping” an air intake to get a quick richen of fuel… or any tricks on how to prime on a rolling starts? think this starts to get into a more advanced topic of tuning on the fly which assuming it primarily just the highspeed jet on the straights.

but wanted to start the topic, see what knowledge people would share.

Although the newer 100cc engines and FA/FSA/ICA engine are air cooled, there’s a big gap in the stresses between a KA and the FA/FSA engines of the late 90’s.

Much higher power output and peak RPM put the FA engines a lot closer to mechanical and thermal failure on a regular basis. Choking was more for preservation than performance. Although you’ll catch some commentators getting this wrong in video coverage from the time.

Here’s some context:

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Agree with James.

This new generation of 100cc engines doesn’t hold much in common with the old ICA engines. It’s a completely different performance category. The KA and VLR are designed to be pretty foolproof/bulletproof engines for the most part, and have a much broader performance window than an ICA would.

About the most you can do for on-the-fly tuning would be tweaking the carb needles every now and then just to liven up the bottom end power if you feel you’re struggling there, or keeping the exhaust temp in the right window with the high-speed needle. While both of these can help the engine perform at it’s peak, it’s worth nothing that there is very little in the way of actual lap time to be gained from totally optimizing these settings. Like I said, the engines are pretty foolproof and won’t require the same fine tuning old 100cc stuff did.

My engine builder specifies an EGT they want the engine to run at for the top-end, I tweak the high-speed needle on-track to hit that target. On starts I sometimes lean down the low-speed needle to keep it from bogging down too much at slow speeds, but very small adjustments, if any.

Choking the airbox is definitely more of a thing of the past. Nothing really runs at that fine of a limit anymore.

I don’t have the experience with the older 2 strokes but did run Yamaha for a few seasons before switching to KA. The KT would require leaning at the start (with a pipe) and adjustment on the fly to keep the temps in check. The KA loads up a little so I usually ride the brakes to bring up revs as we approach the start cone. Any adjustment on the fly is minimal and is usually more to address the weather conditions. I have heard of pinching lines for other classes of motors but have never tried that. I find the KA doesn’t benefit from leaning, it actually runs worse.