Yamaha 90 2 stroke carbs not fully closing

[ollyjscott]

While doing my link and sync last night I noticed that on gentle return to neutral (as you would do when slowly throttling back) the carbs do not fully close and the Middle carb lever needs to be pushed to fully contact the idle adjustment screw. If you 'snap' the throttle lever at the carbs open and release quickly then they will snap shut. I'm guessing this will have an effect on my idle speed as there is a good 1.5mm gap between the lever and the idle screw. Any ideas what could cause this sticking and how to solve (without removing carbs..)?

Issue was there before I touched the carbs for the link and sync

Was idling fine when tested as is 2 weeks ago (800 rpm)
I noticed the individual carb idle air screws were 2 turns out on each carb so maybe the previous owner had compensated for the issue. Factory spec is 1 1/4 turns out.

[greasyshaft]

Try disconnecting the throttle cam from the advance arm and push away from the roller (see illustration). If this solves the problem check your throttle cable adjustment or you will need to do a full sync and link.

Is your engine oil injected? if it is try disconnecting the oil pump linkage and see if the problem is resolved. (sometimes hoses get caught up)



If the shafts are in fact sticking you will have to pull the shafts to clean them.
Also try disconnecting all the carburetor linkages to isolate the problem to which ever shaft may be sticking.

[ollyjscott]

Thanks for the reply and for the diagram. I've checked the function with the throttle link disconnected and it's how I found the issue. It look like I might have to strip and clean the shafts. I'll see how it runs first before doing anything.