QuestionAlright, working on a 73/74 Scrambler 350. I have verified the timing, valves etcetera. The bike fires right up and runs great for quite a while. However, once it has run a while and gotten good and warmed up, it runs terribly. I am getting irritated as any adjustments to the carbs at this point do not seem to make a difference. Let it cool down for a while and it runs good again. Any ideas?
AnswerJared, if the bike starts up cold and runs well with NO choke than there is something wrong with the carburetion.
These bikes are normally cold-blooded and should require full choke to fire up then, progressively less as it warms up. If it starts w/o choke, then it is running too rich.
If the carbs have not been cleaned, it may be time to go through them, replacing the o-rings, etc.
Did you check the mechanical spark advancer for proper operation before you set ignition timing? These commonly stick and that will throw off all of your other settings.
Be sure that the point faces are clean and there is no excessive arcing when the engine is running, indicating either a weak condenser, loose wiring leads or insufficient grounding of the condenser body.
One thing that has become common in these cases, is that the gas cap vent holes plug up with old gas vapors and the the tank will vapor lock, creating a vacuum inside, stopping the flow of fuel. Check inside the cap and clear the small vent holes with carb cleaner or compressed air or something similar.
Will assume that the fuel system is clean, petcock passages are clear and float levels are all set correctly.
Honda used several series of carbs on these bikes and the settings are different for most of them.
Bill Silver
