I just finished resurrecting a 1981 CB750C from the grave. The bike hadn't run in years. The fuel tank had gotten rusty inside, fouling the carbs. I de-rusted and etched the tank with muratic acid, then lined it with POR-15. Then I cleaned the carbs, replaced fuel lines, and installed new carb to airbox boots upon re-assembly. Upon running the bike it wouldn't rev over 7K rpm. After months of troubleshooting in my spare time including 2 more carb overhauls, bypassing the air cut-off valves, bypassing the vaccum fuel valve, checking valve clearance, installing new plugs and plug wires, installing a new battery, checking timing, replacing ignitor boxes, checking the charging system, rechecking everything again and again and again I stumbled onto this site:
www.cb750C.com . Following a suggestion there I checked voltage drop at the coils and found a loss of 2.1 volts! Installing a relay from the battery to the coils resulted in the bike revving right up to red line as it should! In 20+ years of working on motorcycles it's probably the most frustrating problem I've ever had to overcome, but certainly one of the most satisfying now that it's done!
I finshed up with a new clutch, new tires, flushed the front brakes, new chain and sprockets and some TLC. The owner is picking it up this afternoon.
Do you have a C, K, or F model? The fuel tank is pretty model specific, as are the side covers.
Good luck with your new bike!!!
Tom
