Why do you say the earlier K's should beat the F? The F should have the edge on stability and the engine was brought back to and maybe above the earlier performance standards.
I believe (but admittedly don't know for a fact) that while the additional rake an trail provide stability at high speed, it works against the F in the turns.
I was also under the impression the early K's (69-71?) had more horsepower/better engine performance than our F models... ours were too restricted by EPA regulations by 75. So the claimed increase compression ratio and higher RPM didn't make up for all the lost performance given up between the early to mid generation K's.
There are some advantages: The greatest advantage on the track over the K is probably the gear ratio changes. but I'm not sure if the longer duration cam and lightened cam sprocket brought back enough top end power to best the early K's.
Rear disc is of little advantage on the track (at least for a novice like me - may be a different story for more advanced racers).
Don't get me wrong, I love my early F bikes (I've got three and plan to have them all restored at some point). And I do think they are the more refined of the CB750 SOHC bikes... that have spoke wheels.
As far as your holes go I'd like to see one of these Mac baffles chopped in half to increase flow.
Ok.. so drilling those holes was a step in the right direction
However, I really shouldn't have done that unless I gave myself the time to tune for it properly.
The needles can only be worked on with the carbs off. Are you lowering the needles thus leaning mid-range or you lowering the needle CLIP thus richening mid-range?
Based on Hondaman's post (linked above) he actually suggests increasing the main jet and lowering the needle (not the clip position) when running less restrictive pipes (even though this seems counter intuitive)
Why mess with the idle mixture? Surely you're not planning on going that slow 
I guess you didn't see me on the track last year
- yeah, probably not too important for the track, but I figure that could help with the gurgling/popping noise - and may help with initial acceleration from start.
Why not just play with your mains initially and not mess with the needles? Go up one size to 110's and see how it reacts. If you do 2 changes how are you going to know which one benefits you or which one negatively affects you considering the needles and the mains overlap one another? Besides the mains are more top end rpm and I'd like to assume you'll use the transmission to keep it in the upper rpm/horsepower range.
Yeah... I was thinking the same thing... I would focus on the mains (upper 3/4 of the throttle) and if I had time work my way down.
Another thought - the stock muffler is NOT going to allow you to hear things like the Mac does (I have both). Perhaps some of those noises were already happening and you just didn't know it?
Good point. I'm not sure if it's actually backfiring (it's definitely not like a "bang" backfire - just gurgling/popping)... and since the throttle response seems fine, maybe I should leave well enough alone. Do you also hear a lot more gurgling/popping during deceleration on your bike with the MAC exhaust?
Per Hondaman's statement in the link above:
"
in all this, note that the exhaust pipe backpressure plays very, very little into the game until it either disappears altogether (ths increasing overlap scavenge into the pipes, losing it from the cylinders), or becomes so much that the engine can't spit out the burned gases. In other words: from a full set of 4-4 pies to a straight-thru 4-1 header collector with drag shortie length, there is less than 3% possible change, with the stock cam. So, don't fret the exhaust pipe situation."
He was referring to a CB500/550, but I suspect the same applies to the CB750.
Thanks!
