Funny Idle

[TheFoggie]

Hey,

I have a 1982 Yamaha 400XS Heritage Spec. I'm having a few issues with idle. I have recently taken apart the carbs for cleaning but that being said they were in pretty good shape. When doing so I have recently replaced the:

- Spark Plugs
- Carb float valve seat rubber o-ring
- Rubber Pilot jet passage plug
- Pilot Jets (42.5)

The issues is, I'm trying to adjust the idle-screw to try and maintain a constant 1250 RPM. I will set it (after it has warmed up) but after driving a bit and throttling back it will hold at around 3000 RPM, hardly ever dropping. If I turn back the idle-screw slightly it will idle very low at about 900 or less and sometimes stall; so I have to feather the throttle at lights. Right now I'm deal with a bike that idles at 3000 RPM or stalls. I just cannot find a happy medium between to high and to low.

Any Ideas?
Note; looking at pluggs, they look pretty good, but if anything a little rich.

 

[HoughMade]

Try removing the plug over the idle mixture screws and richening up the idle mixture a bit. Photo below for reference.

 

[TheFoggie]

So took off the carbs again, found that the caps had been removed from the idle mixture screws previously; so I took the screws out along with the rest of the hardware, cleaned with carb cleaner (except rubber o-ring... i have learned from previous experiences already) and sprayed through the orifice to remove any debris. For good measure put a little bit of chain oil on the rubber o-ring to keep'er nice and moist and screwed the wee-assembly all the way in and then backed off 3 turns. Wow, what a difference! she drives beautifully now! Thanks for the help and good pic. Houghmade

 

[HoughMade]

Glad it worked out for you!

 

[ZuluWarrior]

I am having the exact same problem so I'll also try this advice.