75 CB750K Runs Rough

[CB750Winger]

   My 75 CB750K idles ok but not great. I also have high rev when shifting or slowing down. The slides seem to operate freely. I've sprayed the intake tubes with no change in idle for vacuum leak. Question: is there a gasket behind the hex intake pipes that go into the head? Do they screw in? Maybe a leak there? Here's what else I've done: complete carb rebuild and sync (3 times) checked everything, new points, plugs, condensers, plug caps, check timing, cleaned and sealed gas tank, compression check, adjust timing chain-ok, everything I can think of. The only thing I have not replaced are the coils. Maybe weak spark? The carbs and jets are all clear. Vac advance works good. #1 plug is sooty but has spark. Any suggestions?

[94thman]

you did not say that you replaced the plug wires. when old these can break down and cause inconsistent spark.

[CB750Winger]

 Correct, I have not replaced the coils or the wires. Do the wires screw into the coils or is this one unit for each one?   Thanks

[94thman]

as to your reply about my problem noise, it turns out, the noise is in the upper end. the right side valves apparently are not getting oil. they look dry as compared to the left side. when i squirted oil on the cam (through the valve adjustment caps) the noise stopped. any ideas on a solution? thanks.

[CB750Winger]

   I hope somebody else jumps in here but this does not sound good. I had the same thing happen on a 73 Yamaha 500 DOHC and locked up the motor. Turned out a piece of the spark plug chipped off and ended up getting stuck in an oil line to the top end. You may end up pulling the valve cover and cams out and turn it over by hand to see if oil is coming up. Next thing would be the head. OR, it could be the sump is partially plugged not pumping enough oil up, or oil pump not working right. You can pull the sump pan under the motor and get to it, I think.....

[woodsrider250-2]

"any ideas on a solution?"

Tear it down.

[CB750Winger]

 I agree with woodsrider. Don't take a chance if it's not getting oil to the top. You'll ruin more than you can imagine. Don't run it til you fix it.

[gonebiking-2]

Remove the plugs, take off the rocker cover, then hit the starter button. Watch where the oil IS coming up and then take note of wher the oils IS NOT coming through the oil gallery. Removed the head and get the galleries cleaned out. While the head is off spin the motor using the starter and see if oil is coming up through all of the oil galleries that fead the top end. If nothing is coming up through the right hand side, then strip the motor and rebuild.