Motorcycle Repair: 1980 honda cb 750, honda cb 750, bill silver

Question
ijust bought a 1980 750k im havig promblem when get on it it wants to max rev. at 6 grand it red lines at 9half i know thats not right and when i ride for awhile it idles up around 2000 to 2500 i took the baffles out of the pipes i didnt know if that is what caused it or not a friend said something about the carbs. needed to be rejetted i dont know i havent worked on bikes

                  THANKS

Answer
Jeremy, if the bike has been sitting for a long time, the main jets could be restricted with old gasoline deposits.

Fast idle and poor performance issues can be traced to:

Intake manifold leaks
Air cut valves diaphragms having holes in them (mount on the side of the carbs)
Petcock (fuel valve) being restricted, causing low float levels under power.
Gas cap vent restricted causing a vapor lock situation.

"Taking the baffles out" to me means that the bike doesn't have the stock exhaust as the OEM pipe baffles are not removeable. Changing the exhaust can cause the jetting to go lean, which will cut top end power. If this is the case, then the main jets will have to be changed.

There is a mechanical spark advancer, located on the left side of the crankshaft, but it runs in oil and usually isn't a problem. If it was damaged or worn, it could cause some fast idle issues.

Spark plugs could be fouled or the plug caps damaged. The plug caps should have 5k ohms and not too much more. Compare the set and if one is way out of tolerance, replace it.

You might check the compression to see if it is all okay. Should be around 170 psi cold with wide open throttle.

If all of this sounds like Greek, then take it to a shop for evaluation. I suspect that the carbs need to be removed and cleaned, at the very least.

Bill Silver