Idle too high

I am having some truble getting thidle set on my 79 ST the idle screw on the bottom in the middle doesent seem to do anything at all, I set all of the air screws to spec...turn all the way until they seat lightly then back out 1 and 1/8 turn, did that and still the idle screw does nothing, it idles at about 2000 when i start it up then when warm it drops to about 1500-1700 rpm but my shop manual says to set it between 500 and 1015 rpm, any advice would be greatly apreciated, im not sure when the last time that the carbs were syncd i have only had the bike about 4 months, i havent tried to sync them since ive had it.

My first check would be the idle adjustment assembly. If you're not seeing (and hearing)the rpm's change when you're moving the adjustment, somethings wrong.

Now that I think about it, if your throttle cable is too tight, and you don't have enough play (~ 2mm) in the throttle cable, that would do the same thing 'cause if the cable's too tight the throttle assembly can't rest on the throttle stop....which I think is what the idle adjustment moves, you'll never be able to adjust your engine speed down. Make sure you can see visible slack with the throttle closed.

Good Luck!

Wait to get them synced and then see how she idles. Other than that ride it and do not worry.

Lube your cables and make sure they can move freely.

It probably won't do any good to sync the carbs with a manometer... you should bench sync first. This puts the slides in the middle of the adjustment range of the idle screw. That is the MAIN purpose of bench sync plus the added benefit of getting the slides fairly close to make sync with a manometer easier.

thanks for the advice, im getting ready to park it for winter as its starting to get a little chilly around here, planning on doing alot to her over the winter though, looks like takin off the carbs will be one of them.

one thing i have noticed after reading about the throttle cable is that the the throttle doesent return all the way back where its supposed to be, you let off of it and it goes back so far but still has about 1/8 of an inch that you have to twist it backwards this makes the idle go down very slightly but not much

sounds like you should pull your cable off and check it to see if it has frayed on either end if it hasn't lube it well see if it moves freely in the outer cable.

6leafclover wrote:

one thing i have noticed after reading about the throttle cable is that the the throttle doesent return all the way back where its supposed to be, you let off of it and it goes back so far but still has about 1/8 of an inch that you have to twist it backwards this makes the idle go down very slightly but not much

Normal throttle stop rests against a spring where position is lowest idle with slides fully down. Twisting throttle further closed against the spring pressure isn't supposed to reduce idle rpm.

Throttle cables may not have enough slack, and may be adjusted at either end to allow more slack. Could experiment by allowing excess slack on both cables to see if it makes any difference toward allowing lower idle rpm by using the thumb screw.

Good Luck!

I think that is my problem when i twist the trottle backwards it feels like its pushing on a spring because when i let off it goes back up just a hair but the idle changes just very little like maybe 100 rpms

I spotted somthing today when i had my tank off, i looked at wg's diagram for the carbs on my bike the one that shows the "connections" i have the vacume fitting on the #3 carb but the two vents on the 2 and 4 carb are capped off, not sure if this is my idle problem or not but i dont see how the bike even runs with these capped but it does pretty well, another thing is from time to time the #1 carb will over flow in short sperts usually until i run it again, it doesent do it all the time, could this be because of the vents being closed? also where is the best place to route the vent hoses