QuestionHi! This bike is running rough, especially at higher rpm's and I am trying to determine if it is ignition or fuel. It generally wont rev higher than 7k. Sometimes fuel leaks from the overflow tubes which leads me to believe there is trash in the carbs, but I want to rule out the ignition before I tear the carbs apart. Any help and test procedures would be greatly appreciated.
AnswerMike, it is a little harder to check the timing and spark advance outputs on the DOHC fours, due to the fact that the timing marks and advancer are bathed in oil.
Most of the bike stories I hear about 29 year old bikes are to do with fuel/air blockages in the carburetors or petcock. These parts have seen a lot of time submerged in various gasoline forms, that have evaporated and left deposits behind in critical areas.
Fuel from the overflow tubes, indicates float valves that are leaking or floats that are out of specifications or are damaged in some fashion.
There is a whole array of checking to do on the electrical side that can cause misfiring. These bikes have known issues with charging systems, and a low output alternator will cause misfiring at the transistorized spark units. There are carbon brushes that need to be inspected, the rotor tracks checked for resistance values, as well as the spark plug caps tested (5k ohms). There are online parts illustrations at www.bikebandit.com www.cmsnl.com (with real Honda part numbers).
I would take each and every electrical connector apart and check for corrosion and damage to connector pins. Verify all harness and engine grounds are clean and tight.
Electrosport.com site has online diagnostic charts for testing the charging systems.
You didn't say how many miles are on the bike and what kind of care history it has had through the years, so any or all of the above factors could play a part in misfiring engines. Once you are satisfied with the electrical system, then you can do what probably really needs doing... cleaning the fuel system from gas cap to float bowls.
If you discover that the spark units, mounted back by the battery are melting/dying there are aftermarket ones made now http://www.pazon.com/files/PDF/HONDACB.pdf
Bill Silver
