kt100 what to do to make it a open

brad. overbore,slightly -porting, some
carb work and moneyor do it your self. have a super-dyne 107 cc stock appearing if you want to go that way. 1 race fresh i believe? buyout motor ran in FAS series. on jackshaft or off TSOW pipe was pretty fast, not allowed in stock app! too many cc.carb done and ready! john
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That is going to be some hard information to come by I would think. I have recently bought me 2 KT100 motors with 4 separate jugs. One of those motors was blueprinted by a big name builder the extra jugs are for me to screw up and throw away. I degreed all of the ports, checked the timing, measured the squish, cc'd the head and looked at carb settings. Just by knowing the specs does not make you an engine builder though and I do not claim to be. (just a bored racer) It takes understanding of how things work and skill to do what needs to be done. There is a lot of money to be spent on research of how to build a competitive motor for any class. This is why many people or skittish about giving out all of there little secrets. Good Luck!

Ted Hamilton

Helmet Painter / Racer
Blake -- ditching the JICA's? :) As far as the KT goes, Pete at Superdyne has an idea in mind to make it a 125 -- reasonably priced. Give him a call and he'll set ya' up. Unless you want to machine it yourself. I'm slowly learning that learning to do it yourself is fun, but expensive in terms of money and most of all, time. There isn't much that hasn't been tried and most people end up trying to make 'em match the Euro 2 cycles in the end... But it's fun to make chips fly. There's a reed block conversion option that I'd try....Steve O'Hara and Pete Muller might have some good ideas too.
Blake -- ditching the JICA's? :)

Not a chance. I just got them back from getting a little port work done, top end rebuild and a set of alky 360A Tillotsons to go on them. Going to switch to the L2 pipe and good Tomar 3 disk clutches. Maybe after this I will have all of the week links worked out that have bit me in the past.

The KT100 motors are just something to do on the spare time...what little I have.


Here's the question, Why do you want to make a KT open? You can buy a great 100cc reed or rotary engine and make more hp with it, in stock form. If you have a KT class, great, I understand. If you are just playing around, go get a stock Sudam on alcohol. Hilton has a pile of them.

If you want to play with KTs, fine. If you want to be competitive, spend your money on something else.

Good Luck,


Mike, we have plenty of horsepower motors. 116 rotaries, wet 100 cc pcrs, 116 reeds, even a 70+ horse 265cc trannyless Honda. Very competitive at most places we go, except one track that is almost field sand. The bigger motors blow the tires off no matter what setup or how much we kill the tires. STOCK KT actually yields better lap times, just need to squeeze 5 or 6 more horse and some more torque out of it.
The little yellow book that came in the box with new engines yrs. back has most everything you need to know to get started , what and where to cut. Name of book is; Yamaha, KT-100S, (Engine Assembly), Owner's Service manual , Lit-11626-03-25, 7U5-28199-10.
How much for the stock appearing? Is it legal for stock appearing at Daytona? I want to run the Yamaha class as well as UAS down there......especially to try and get a read on tires for Sunday.


How much for the stock appearing? Is it legal for stock appearing at Daytona? I want to run the Yamaha class as well as UAS down there......especially to try and get a read on tires for Sunday.
As posted on Daytona Yamaha thread:

Stock Yamaha WKA legal at 360 lb

Daytona Stock Appearing at 390 lb
Walbro WB3A carb drilled as desired
Methanol or Gas only
No Strokers
No Reeds
Up to 55 mm Piston (making the engine a 109cc)
Port and Polish as desired


Any Pipe for both weights
Another big problem with the KT as an open engine is the relatively poor ign. sys., compared to Motoplat and Seletra systems, also the rod is decidedly inferior to the forged ones in any of the IAME engines. So you would need to add another $400. or so compared to any of the other orig. reed and/or rotary valve engines. The best part of the KT's , is that there are dozens of them out there, and they are relatively cheap, with new parts still available.
terry. mine is 107 cc . got it in a buyout in fle. troy and zac were just her this am and we fire it up. super dyne motor. maybve monty or bull dog can tell you more? it is on jackhaft w/ tsow pipe as it was ran last yr..sounds strong and ans the throtle like i wants to go. on 05 velocity..


New member
The superdyne that was Montys is real fast and reliable has sudam piston, Honda cr rod, 30 mm walbro custom cut, cant break it I wanted it but pete can make me one if I want.. he makes a good 125 Yamaha hehe...montys Yamaha ran with reeds no problem...who ever buys it needs to call pete and give him the number on the exhaust flange so he can pull the file card and get with the new owner for tuning purposes...that motor also has a cut keyway in it and needs to be there to retard the motor...great engine!
thanks mike and rooster. zac-troy intrested -terry intrested ? will not sell till i get all the dope on it! john. sounds stout ! w/ j-shaft -pipe and 3 disc bully!


New member
Hey guys i have a fine rotary 116 that mr clausen built for me.i am just looking for a winter project when im not racing.i would like to build myself a kt 100 out of a beat up one i have.i have access to a machine shop.its just something for me to do just as a guy builds a classic car.i know its a hunk of junk.i dont care if it lasted a race.i just want something to do.thank u