You got it correct Pete. I still have both pipes. I still don't have my first attempt at a KT100 DD dialed. It really falls on it's face below 8k. I'm right at the WKA numbers. I'm unsure if that is part of the problem, or it has bad blowdown which I never measured. Or maybe I'm just too used to the K35 DD. I'm considering dragging it to Santa Maria next year just to put a smile on your face while smelling R40 again.Many, MANY years ago I set up a sprint kart with a direct-drive Yam. Engine was to the WKA specs, except I ran the intake port .025" milder than the spec. I also ran a 10-96 at our local sprint track (Santa Maria, CA).
I ran a dd pipe I picked up in Australia called the "Hot Dog", which I think I got from St. George Kart Centre back in those days. It was a very "Vevey"-style exhaust pipe (dead-straight exhaust pipe, so it required one of those original OEM Yamaha long/curved headers).
The engine would pull cleanly (and well) from 7000 to 17000 rpm with that setup.
Probably one of those most fun go karts I've ever driven, and it required virtually no maintenance.
I gave two of those pipe (new in box) to one of the guys that visits this forum... let me chase down his username here, and maybe you could contact him and get him to take some dimensions off that pipe.
edit: I think the user: moebiusgold might be the correct username for my friend that has the pipes. Don't hold me to it though...
PM
You got it correct Pete. I still have both pipes. I still don't have my first attempt at a KT100 DD dialed. It really falls on it's face below 8k. I'm right at the WKA numbers. I'm unsure if that is part of the problem, or it has bad blowdown which I never measured. Or maybe I'm just too used to the K35 DD. I'm considering dragging it to Santa Maria next year just to put a smile on your face while smelling R40 again.
I'm sure you are correct that less intake timing will help. Some more flex might help too.You may be expecting a lot out of a DD Yamaha! haha!
Try going .025"-.030" milder on the intake timing. I remember mine pulling quite well in the low 7000's