Yamaha KT100 on race gas

[DAVE FAITZ]

It seems that I have found no way to get 110 octane fuel to perform or create the torque and horsepower that standard pump gas can develop. Even on the track with race gas these Yamahas just dont go. Am I missing something here ? I see it on the dyno and the track. Some get them to hit hard on the bottom ? I cannot. Same old thing in karting with fuel ?

[Jim McMahon]

Well what have you tried to get more power from the 110? Are you running pipe or can? Is it being tuned for a KT100 class or something else? Generally you will need to add advance and or increase compression at least to see any benefits from the 110 and then at that point you will be reducing your overrev so it could end up being a wash.

You might be better off with low octane marine fuel (no ethanol) if you are looking to gain performance with a KT. They don't make a lot of power at least not without modifying them to the point where it makes more sense to just get a different motor.
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[al nunley]

It would be foolish not to believe your eyes, your dyno or your lap times.
Find some other reason others are having better low end performance. I could write a book on this subject.
The first chapter would be on how to find if you have a good engine.
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If the data does not support the theory, get a new theory. (Al Nunley)
All else being equal; Compression is the Holy Grail.
45 years, in and around karting

[Volker Krahn]

[Mark Horne]

110 race fuel will not produce more power unless the engine requires it. A Yamaha is a low compression motor and does not require the extra octane.

These are the steps we follow to ensure maximum over power output from our Yamahas:
1) Test all the carbs to find the best one. Most perform about the same BUT, some or one will be much better than the rest.
2) Have your engine builder send the cases to Pete Mueller. What you get back will be spot on square.
3) Have your cylinder squared up
4) Be sure the crank and rod are perfectly square
5) Minimize gasket stacks under the cylinder. If your engine builder uses aluminum shims (shaped like the gasket) and a .005" gasket on top and bottom of that, you will have your best chance to maintain the squareness of the assembly. A stack of paper gaskets will or could cause a loss of square.
6) Have the engine Dyno tested and hook the clutch up right on or 100 rpm before peak torque.

Just as a side note, thinking out loud. Sometimes what looks like good bottom end power comes from the competitor using a higher numerical gear ratio (7:1 vs 6.8:1). The 7:1 will pull better, as I am sure you know, but the engine must be tuned to turn higher RPMs. This gives the engine more leverage throughout the RPM range. If you are closing in on the competition at the end of the straight, you may need to change your setup (pipe, header gear) for more RPM. If they pull you just off the corner and then you can stay with them, and you have already made sure the engine is good as noted above, some flex/header/pipe/gear combination change may be needed.
We use triggers on the carbs as well, (Road Racing but still good for Sprints) because you can dump more fuel in at peak torque tricking the pipe into reacting as though it were longer, and then lean it down as the RPM increases to maximize top RPM by tricking the pipe/ exhaust into reacting as though it were shorter.
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