Wez_
CB750 Addict
Just watched your utube vieo posted above. It appears your top end is full of carbon. I understand you want the bike to run without going too deep into the motor, but from the color of the exhaust during the revs, it appears there is carbon build up. When you rev the motor not under load, I would expect to see white smoke (briefly in your video), not browninsh. With the headers off, you can look into the exhaust valves and see their condition. The intake valves will likely be in the exact same condition. If those bad boys are all gummed up, then that could be why you have higher compression (excess carbon causing a better "seal" around the valves. This is not ideal. Also, with the condition of that gas tank, it's likely that gunk got in the carbs and the poor efficiency of the motor built up excess carbon deposit. It's not ideal to gauge a motors condition from a thermal test of headers on an air cooled motor neither. Ideally, you dont want an air cooled motor to idle like that no longer than 5 minutes ( not enough time to heat up properly) use compression and leak down tests aside from visual inspections. Try the scrubbing the exhaust valves with SeaFoam brand spray from the parts store. Get one of those air gun cleaning kits and use the brushes to brush down the valves from the outside of the motor with the headers removed. if you are really handy, you can make a shop vac hose attachment out of a soda bottle and tape it with gorilla glue tape to be a nice and small cone shape. put it on the end of your shop vac and suck out all the carbon and Sea Foam spray to clean the valves the best as possible. My heads came off as soon as I saw the condition of the exhaust valves. Even AMC told me to just do a compression test. I don't like running that crap in my motor. Clean that top end and you might have the improvements your looking for. Aside from that, a few trips around town might blow some of that out.
My heads before
My heads after disassembly/cleaning
My heads before
My heads after disassembly/cleaning