Some stuff I tested once upon a time...
The 4into1 and 4into4 exhaust stuff ....I had 3 types of 4-1, a brand new set of std 500-4 pipes, and a good set of std 550K3 pipes....The 4into4 550K3 pipes were by far the best..that was on a 500 a 550 and my 610 motors. No 4into1 got near them, they just made a better noise...
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Another thing I have tested is carbs...I have tried the stock 500 carbs...the stock 550 carbs and a set of 750 F2 carbs..modified.....again the best were the 550 carbs....the screw in jet type...not the push in. I have obviously religiously jetted them all. The 550 carbs on my bike at the moment with a 610 motor do 55mpg..super smooth right through with no glitches/flatspots..and I thrash the turdy out of the bike all the time...its always around the 100mph mark. With the 500four carbs - although performance doesn't suffer - it never does more than 33mpg...
? The larger 750 carbs just weren't worth the effort....performed exactly as the 500four originals....I did all this when I raced the bike in 85-86.
Camshafts... I have 3 extra camshafts for it...a Yoshimura road and track (crap)...A yoshi IOM race (OK)...and one I had made by Joy cams...which was welded and reground to XL125 motocrosser profiles...(awesome 8,000-10500rpm)...she used to rev her tits off...great for racing but not too good on the road.
I did all this when I raced the bike in 85-86. My 500four bored to 610 was exactly the same speed as a GPZ600 on snetterton straight.