I know this doesn't belong in the sohc4 forum, but my brother has a 1981 cm400t that is having a little bit of a carb issue. It won't idle unless it is around 1500-2000rpm. The ignition system completely checks out - both spark plugs produce a bright blue spark. The carbs are of the CV type and are perfectly clean and synchronized, but I found that there is a little black plug in the passage between the main and idle jet and it is deteriorating. It looks to provide some sort of important seal. I also found that there is a direct passage in between the idle jet passage and this mystery passage. It seems to me that this little plug is the only thing wrong with the carbs on this bike - but I don't know what it does...
Can anybody provide some insight on this problem?
If it makes any difference, my other brother has a 1981 cb650 with the CV type carbs as well and, on all four of his carbs, this little plug is missing. The cb650 won't idle at all. It has perfect ignition and pristine, recently rebuilt carbs, but for some reason, the mystery passage that these carbs have in common with the cm400 have no plug in them and the bike just wants to race it's engine. Maybe that missing plug has something to do with it?
Any help is much appreciated.
