Using vp ms98 fuel for testing but are there any other options for testing since 106$ for a 5-gal pail is a lot (20+$ per gal). Are there any other options that do not affect performance much? Or is vp the only option?
Yes. You need at least 98 RON. 91 octane pump gas is well below this and will damage a KA100.
If you live out East, 93-octane pump gas meets this spec. Marathon/Speedway premium from the Detroit refinery is 101 RON. You’ll have to enrich the mixture a little because of the 3% oxygen content.
If not, you’ll have to get a little creative. Out in California, many commercial-fueling stations have a race gas pump - I can buy Sunoco Super Sport 100 Unleaded for nine bucks a gallon at my local cardlock. Away from CARB’s control, you can usually go to the airport and buy 100LL aviation gasoline for about five bucks a gallon. I won’t use it out of principle because it is leaded. If you’re completely stuck with just street fuels, mixing E25 from 91 octane pump gas and E85 will get you 100 RON, but the mixture will be WAY off and extensive tuning will be necessary.
There are other options but they are all expensive. If you are near a race track most classes use fuel similar to what we use in karts. They usually sell in bulk vs the 5 gallon pail so the cost is less per gallon. Sunoco has a few options as well as VP. The disadvantage of this is the fuel might not be fresh and you need to store it in something if you didn’t save the pail.
I use VP C9 and it seems to do well. Although I have my own thoughts, I’d like to hear from an engine builder on fuel requirements.
This might be a stupid question, as I’m not a 2 stroke person, but I assumed the fuel was spec right?
At national events yes, at lower levels it isn’t always. Around my neck of the woods it has to be ethanol free non-oxygenated though.
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Most of the clubs we run in Texas, and the regional series, the fuel is spec. At times, when the regional/national series switch fuels, the club races will allow you to run either for a year.