QuestionMy Honda 50cc engine will start but you have to apply gas. And won't idle cold. When it warms up its OK. I messed with the lean screw and it didn't help. I put a new Mikuni 15mm carb on it as the old one was shot. The choke has no affect when its cold? Shouldn't it help? The old carb it started cold and idled great.
Thanks
AnswerJohn... Honda 50cc what?????? 4 stroke, 2 stroke, dirt bike, street bike, scooter???? What year??? They are all different.
The idle mixture screws on a carburetor are for when the engine is fully warmed and at normal idle speed. If you richen it up to compensate for poor cold running, then the engine will be too rich when it warms up.
If the bike doesn't run well when cold, then the choke circuits are not functioning normally or the ignition timing could be incorrect or the engine compression is low due to worn rings/tight valve clearances. Air leaks in the intake tract will lean things out so much that the choke system can't overcome it, in some cases.
Honda don't come with Mikuni carbs, so it is hard to say what the jetting in the carb is, compared to what Honda wants for the Keihin carb, that the bike came with. Carburetors are calibrated for specific applications.
You have to establish a baseline to work from: Compression check, ignition timing check, intake system check for air leaks at the manifold, etc. Any changes to the exhaust system or air filter will require different jetting for the carburetor.
Choke systems are either designed to restrict the flow of air by turning a butterfly valve or by use of an enrichening system that adds extra fuel/air when the lever is activated.
Bill Silver
