Motorcycle Repair: Honda CB 350 one cylinder only, honda cb 350, point gap

Question
Bill,


  I have a '72 cb350 in good working order except for the right cylinder. It only fires when the bike is hot. As the engine is warming up using just the left cylinder the right one begins to back-fire and eventually begins to operate. I set the gap on both points exactly the same. Is it possible for one cylinder to be out of timing and not the other? I got the bike last May from someone who had not run it for aboiut a year. Thanks.


R/ Bill Lynn

Answer
Bill, you need to do a full checkup of the bike, first.
Valve adjustment, compression check, ignition timing check at idle and at full advance and a fresh set of plugs. Then, leave the point cover off when cold and watch for excessive arcing across either set of points. IF that is the case and the points have been properly cleaned and the gap adjusted to .014-.016" with the points set to open at the F and LF (firing) marks, then the condenser could either be defective or the leads to it are loose under the fuel tank, where the coils are connected to the points/condenser and power harness.

Setting the gap the same doesn't ensure accurate timing, which is why there is a slot on the backing plate, to allow for the point plate to move back and forth to allow for proper timing. Set the gaps first, then move the backing plate so the L side points are opening at the LF alignment, then either move the right side point plate, if adjustable, or slightly change the point gap until the right side opens at the F mark. You might want to remove the point plate, inspect the mechanical advancer for proper movement..advance/return and lube the point cam with point cam grease, while you are fiddling with the points.

Check the spark plug cap resistance... around 5K ohms and be sure that it is screwed on tight to the end of the plug wire.

After all of that, you need to be able to verify that both of the carbs are opening at the same time. With fuel tank loose at the back, you can usually see the throttle cables and levers move. Watch for movement at the throttle levers when you slightly open the throttle. Both should move at the same time. If not, then the cables need adjustment to cure the problem.

Bill Silver