Motorcycle Repair: honda cb77

Question
hi bill , l have a 1966 honda cb77 usa model it seems to be running colder on the right hand cylinder , any ideas what it could be , cheers keith

Answer
Keith, You have to start at the beginning... adjust valves and then test compression. Most CB77s have about 175 psi.  Honda book shows minimum 10.5kg/cm which is 150 psi equivalent. If you have two happy cylinders with those readings, then you have to start looking at other systems... IF not you need to pull the top end off and check valves for leaking and pistons/rings for wear beyond limits.

Fuel:
Float level inaccurately set... should be 22.5mm
Idle jet plugged up... #42 usually
Warped carb flanges
Flattened/leaking o-rings on carb flanges and insulators
With the diluted US gasolines, I am using #140 main jets for improved performance.
Set both carbs the same at idle with mixture screws out about 1 turn. I synchronize them by removing the float bowls and main jet holders, so I can see the ends of the needles. Adjust the cables so they both raise and lower at the same time. This is the LAST step to do after you have settled down idle mixtures and ignition timing.

Ignition:
Incorrect ignition timing on one side... check with bike running and make sure that spark timing does NOT over advance past the II marks on the rotor for either side. There are issues with the point cams loosening in the camshafts, causing point cam wobble, which leads to inaccurate ignition timing. Set both at the F marks and one will probably be off the mark at full advance. Set them both at full advance marks and then one will be off at idle. Spark advancers can loosen up at the rivets and the return springs can stretch out or break. Advancer weight rubber stoppers can degrade and fall out, causing too large of a swing in the spark advance mechanism.

Make sure you don't have exhaust leaks at the header pipe flange where it meets the cylinder head exhaust ports and at the muffler connections.

Bill Silver
www.vintagehonda.com