78XS400 idle problem

[78XS400]

hey guys, new to the forum, but i hope to be a long time poster. I just bought this bike, and i really wanna start learning about bike mechanics (im already a car mechanic by trade, but i dont wanna go messing with bike engines just yet on my own)

its a 78 yamaha xs400, (was told it had a 1980 engine put in tho), the only thing ive noticed, is that after warmed, bike will idle at 2000-3000 at a red light, in neutral, or in 1st gear with clutch depressed. Only way to prevent this, is to press the brake, and have the clutch slip (friction point), that keeps the revs down, but thats not good for the clutch.

Im thinking..... sticking throttle cable? choke? carb problem? Not asking for a miracle answer, but sum advice as to wat kind of steps i should take, would sooooo appriciated. This is my first bike, and im definatly gonna be a long time rider, so any help is great. Everyone starts off as a newbie thanks alot.[/code]

[mgdavis]

Start by simply trying to adjust the idle down. There should be a knob at the carb (or carbs). I had the same issue with a '79 CB750, it was fixed handily in that manner. On my bike it was a black plastic knob between the carbs.

[mydlyfkryzis]

It may also be a vacuum leak. Vacuum leaks can cause high idle speeds...

[78XS400]

so i should start sprayin sum intake cleaner around vacuum lines first? see if the idle raises anywhere?

[mgdavis]

So I should start spraying some intake cleaner around vacuum lines first, to see if the idle raises anywhere?

There, I fixed it for you.

"Intake cleaner" makes me think that you mean carb cleaner. I'd try WD-40 around the boots between the airbox and carbs. Wipe things down afterward, WD-40 can cause rubber to dry out. If that doesn't make the idle change, start looking for the idle adjustment. Did the idle change after work was done on the bike, or was it spontaneous?

[78XS400]

No work has been done to it lately, i just bought the thing. Im going to eventually do a tuneup when I get the chance and the know-how. Carbs should be balanced, and shouldnt be in that bad of shape, it runs pretty nice. The thing I just noticed this morning.... is theres no hose clamps around the boots going into the carb, im gonna try to install some, see what happens. Thanks again, ill keep you guys posted.

[beardking]

Just as something to look at, make sure that your choke valves are seating fully when you turn off the choke..

[dablade]

If you don't want to hose everything down with carb cleaner or WD-40 to find a vacuum leak, you could try propane. attach a small hose to the end of a propane torch, turn on a little and place the hose near where you need to check. Works good, but less mess.

Regards,

Perry

[mgdavis]

:flame: