Trey,
Luckily, there is a bunch of old magazine articles with drag strip stats that may be used as reference. If I have this right, you have a basically dead stock 1974? cb750 with a serious effort made to reduce weight (to 420lbs correct?) from +/- 510lbs. And you are currently running 16/50 (3.12) and are running in the neighborhood of 2.2 60ft, and low 14s at 90mph?
As a reference, Bob Braverman did a series of articles(7 part series ...Trey, you know of what I speak
) based on a dead stock 1973 cb750 and went through MANY steps all the way out, several articles later, to a RC Engineering built 1000cc motor and lightened the bike to 399lbs with oil/no gas.
They started by running the dead stock 1973 (110 main jets) bike, stock 341 exhaust, 18/48 (2.66) gearing and all, and ran 13.8 at 97.50 mph
Then they dropped the gearing to 17/48 (2.82) (still 110 main jets) and ran 13.68 at 97.33 mph
Then they swapped in an Action Fours 4 into 2 exhaust (still 110 main jets) and ran 13.44 at 99.80mph
Now, as the 1973 is basically identical to the 1974 model performance wise stock, this should be a good baseline reference.
For some reason, they were running lower ETs and higher mph than you carrying another +/- 90lbs bike weight (420 vs 510).
This suggests to me that your stock motor is ...perhaps ...putting out less power than a fresh off the showroom motor. High 13s were the norm in dead stock trim during that period.
That (wonderful, BTW) 90lbs your bike has lost may well give you a +/- .3 to .4 ET advantage over a dead stock weight bike. That perhaps would have put the above dead stock 13.8 into the 13.4 to 13.5 ET range at about 100mph. Reducing the same amount from the stock bike with added Action Fours 4 into 2 exhaust and 17/48 gearing time of 13.44 at 99.8mph your 90lb lighter bike should be in the range of 13.04 to 13.14 at 102mph or so.
It would be interesting to see how your bike would run with 17/48 gearing just for an apples to apples comparison. If you are way off the mark
of low 13s at 100mph (given a good 60ft) with 17/48 gears and 110 main jets, I would think that your stock motor is no longer making 1974 stock power for some reason.
It's probably not fair to expect your 40 year old motor to still put out what it once did. Rings get old, pistons/cylinder walls get worn, compression drops a bit, valves get carboned up and loose their perfect seal, etc, etc.
FWIW, by the end of the part 1 article, they had an Action Fours 811 kit installed, Champion RG505 plugs, Kenny Harmon "D" grind cam, velocity stacks, megaphone exhaust, 16/51 (3.18) gearing, and ran 11.99 at 110mph at about 490lbs bike weight. Not bad...
George
