Forum

[tippi]

Here comes the situation/problem: engine has normal ops temp. and idling is fine (on center stand after a ride), it idles with constant revs - nice, I am happy. Suddenly, after 40 to 50secs, there is a noise like "paff", revs decrease in a way that the engine hardly keeps running; then, may be 3 or 4 secs later, revs increase to the level before the "paff"! This mysterious decrease/encrease idling behaviour happens in a more or less regular period when leaving the bike on the stand; there are no external reasons such as playing with the throttle, and ignition, fuel pipe/filter, carb jets etc. are all ok (engine runs fine under all conditions, except he above). Do you think I have a problem with the float so that it comes to a lack of fuel (but why should this happen only during idle)? Any thoughts and/or experience? Thank you very much, Peter.

[Mark M]

It could be that the carb body and slide have excess wear. How old is the Concentric? The original type don't last long in my experience. The new "Premier" type are made of a more suitable material and look like they will perform better for longer. An easy way to check for wear is to raise the slide well off it's stop (about 1/3rd is good,) and try and rock it back and forth with your fingers through the inlet. Any significant movement suggests something is worn. That would be the first thing I'd check.

REgards, Mark

[simon]

Had this issue with my B44 Shooting Star. Turned out the bob weight springs on the auto advance weren't tight enough to return the ignition to a proper retard position. The way to tell if its a worn slide is to just take the weightonto the throttle cable without actually raising he revs. If it changes noticably then the slide or the body or both are worn

[Rattlebattle]

Doesn't sound like a carb problem to me; more likely to be ignition.