my 95ish Tigershark Daytona 640 takes a while to climb from 4000 to 7000 rpms. it gets to 4k very quick but after that its a struggle.
I've rebuilt both carbs and adjusted the high speed screw in and out and found that 1 turn out is the best. if i go an 1/8th leaner or richer it likely wont get above 5k rpms. at 1 turn, it will get to 7k in about 20 seconds and will run good if i keep the RPM above 6k.

Only other observation I have is that the ski smokes a lot. a lot more than my Polaris 650. At all speeds i see a lot of smoke coming out with the exhaust where as i'd typically expect it to be barely noticeable once the engine is warm.

I adjusted the oil injection arm so it will fully release when the throttle is closed.

My next thought is to get an oil injection block off plate and try pre-mix.

Any other ideas? Compression is 160psi in the front cylinder and 150 in the rear and I use premium non-ox gas.