Expert: Dan Liddy - 6/17/2005

Question
Hi Dan,
I have a Yamaha KT100J kart engine, I recently found out that it is possible to alter the oil:fuel ratio from 20:1 - 25:1. At present most reccommend 20:1 but a few engine builders say the leaner ratio is quite fine. Before I intend to alter ratio's ive switched oils from Castrol R30 to Elf HTX 976; which is virtually the best kart competition lubricant available. In conjunction ive also switched from denser lower grade pump fuel to the less dense Elf BFK07 fuel (which would mean a higher flow rate). With the full synthetic oil and less denser fuel I am positive that the leaner ratio will be not a problem but I have to have a professional opinion.
Sincerely,
Jay Schrodter.

Answer
Hello Jay:

Your best professional opinions would be available through Yamaha.   They have the staff, engineers, and racing expertise to offer you sound advice based on study. I am anything but a professional, and my two stroke experiences ended before electronic ignition !

I can only say that if some engine builders feel that 25:1 is safe, than it's worth listening to them.  If th engine will run on a mixture that lean, then it should make a difference in power output. If it melts, well, we live and learn.

In my own instance, I am able to use exhaust gas temperature guages to monitor internal engine temperature, and if I see the temp rising above about 1400 Deg. F. we ease off some , and change jets (or ignition advnace) before racing again. Obviously we try to make these decisions during practice and qualifying rather than in a race, but then sometimes time- - - well you know.

Good luck with your racing, I wish we'd had karts when I was young, I'd be a lot better driver now.

Best wishes,

Dan Liddy
Sarasota, Florida