Stuttering engine

[Craig 8150]

ivenhad my Yamaha xs650 flat tracker for about 4 months now with various little niggles .but my issue at the moment is the engine stutters when around 3-3.5 thou revs. I have new plugs in it new fuel filters,the mixture has been set by my friend who knows these engines side out ( he races in the world motocross side car championship ) . He will tinker about some more when he has time but for myself it's bugging me .imhave mikuni carbs on it with foam air filters. It's only recently been doing this after being trouble free for some time.

[eastanglianbiker]

are you sure its not a jetting problem as its at about 3000 rpm that the main jet takes over from the primary jet,try riding it with choke slightly on which will allow more fuel through and see if the problem goes if it does then main jet size needs to be increased slightly

[Craig 8150]

My thoughts are this , it has been fine for a while so jet must be correct . I believe the bike had not been run much prior to my buying it . Having recently cleaned out my fuel tank for re sealing and kept the contents in a bottle I am aware of the gunk that collects in the tank it's surprising ! Plus a fuel filter was heavily clogged , both now replaced . So I'd imagine that it's entirely plausible jets etc can be blocked as a result . I may well get them ultra sonically cleaned . And a good mechanic that was recommended to me has already stated that the carbs are not balanced also .

[Stu]

balancing wont affect the carbs at 3k

it does sound fuel related

hows the air filter?

the choke trick is a good place to start its free and easy to check

[Craig 8150]

I shall clean the air filters tomorrow , the carb balance was an observation by mechanic in passing.stu .on another note though whilst finally getting a run out today the clutch started playing up only pulling away in first gear , other gear changes were fine it has been mentioned of a worm screw problem etc , then .....a short while later ..clunk ...?? .i look down at rear wheel to see a bar ( strut thingy ,attached from the brake hub into the engine now having broke of the engine fixing and pointing rear wards . The rear brake arm loose with the threaded rod attachment wrapped completely around itself ...number plate gone and metal backing well bent . I have no idea as to what happened there but confess my daisy girl ( yes she has a name ) is faltering often and is requiring TLC .....often !!