Motorcycle Repair: 1978 CB550K, valve stem seals, valve stems

Question
Hi,
 I own a 1978 CB550 K. I have three main concerns

1. The bike starts and runs fine, but will not idle any lower than about 1,300 RPM, normally at 1,800-2,000 RPM.

2.At startup, hot or cold, white/gray smoke will come out of the 4 into 2 pipes, mostly out of the left side.

3.I am fairly sure the petcock is leaking, mostly because the bike will run fine in the off position.

The previous owner (family member) had the bike repaired/maintained by a friend who works at a Honda dealership, so the carbs are clean. What are the possible solutions? Also, I can still have the bike serviced by the same person, but I can't figure out why these problems were not addressed in the first place.

Answer
Matt, you didn't mention the mileage on the bike and overall condition of the engine. A compression check is always a good idea to help me understand the condition of things inside. Bear in mind that at any mileage, the valve stems are 24 years old and a source of oil consumption and smoke, especially at start up or after prolonged coasting down hills or idling.

If the carbs were rebuilt and the individual synchronization screws not set at the original height, the idle speed screw can become ineffective.

High idle speeds can also be induced by sticking spark advancers, air leaks at the manifolds and often by incorrect ignition timing.

Cold start smoke is often just condensation, if it is white. Blue smoke indicates oil consumption, black smoke is excessive fuel.

Your smoke condition could be worsened if the bike is parked on the side stand, as the oil also flows that way in the cylinder head, surrounding the valve stem seals on the left.

You can pull the fuel line off the petcock and put a small piece on the end, draining into a small container to see what positions the fuel valve is working in. They are not rebuildable, so a replacement may be in order.

Bill Silver