Motorcycle Repair/1971 Honda CB350 K3 12K miles
Bike has free flow ehaust with OEM air cleaners with a bad stumble between 1800- 2500 RRM, high 3000RPM idle after warmmed-up would settle back to 1000 RPM. I figured CV slides were sticking and it needed an entire cleaning. Dipped carbs/parts, CV diaphram is not torn-no holes, new gasket rebuid kit, larger main and secondary jets for free flow exhaust and velocity stacks were installed. This has corrected the previous 2K RPM stumble with OEM air cleaners. Bike runs strong off bottom to 9K. Short amount of miles after these upgrades-after bike is warmed up, LH piston does not seem to be firing- more quiet at exhaust tip and exhaust pressure much less than RH side. Compression is 128 LH and 142 RH. Lightly emery cloth cleaned points, set points at .012" have nice spark there no arching, RH plug dark with strong spark, LH plug wet/dark weak spark. Coil- Ohms at primary wires about <1.5 Ohms or less. At plug wire about >6K Ohms or less. Have I missed anything? Have the coils gone bad? Please help!
Compression readings should be in the 175 psi range with throttle held wide open. Honda books show 153 to 187 psi range as standard. Readjust the valve clearances and check again. If even and low on both sides, either the motor is worn out or the cam timing is off a tooth.
Ignition coil primary resistance readings should be about 4.5 ohms. I have started seeing a lot of failing coils on 350-450s in the recent past, so I suspect the LH coil is dying.
I would set the point gaps up to .014-.016" When the points gaps are down too low, there is the possibility of the coils sharing current draw from both coils momentarily. They need to take turns, so ensure that the gaps are wider than narrower to prevent current sharing from happening. If that is happening the engine will run poorly due to lowered coil voltage.
Intermittent high idle often comes from sticking spark advancer weights, so pull the point plate, remove the advancer and clean/lube the points cam and ensure that the return springs are doing their job.