High idle

[Bbqman]

I have a hs40 on my bike. Cleaned the carb in the tank and put all new o-rings and gaskets. The problem is the idle. It idle to high. I even have the idle adjust backed off to where it's not touching. Sometimes it will be at a good idle then takes off without doing anything. I have all new gaskets on the intake and cleaned all the offices in the carb body. Am I getting air from somewhere? Throttle shaft? Thanks in advance

 

[Mariah]

Check the throttle plate to be sure it is seated in the middle of the hole with the throttle shaft fully closed. If it is off center it will bind up before it touches the idle screw, vibration will sometimes shake it loose and let it close fully. This would cause random idle speeds.

 

[mustangfrank]

Yep to above. I just had an HM series giving me fits with a random/racing idle, PO torqued/twisted the governor mount on the shaft, even gov adjusted properly didn't fix, had to swap in another gov assy...translation, check gov adjustment. The little passages for the idle circuit get plugged easily too.

 

[Bbqman]

Yep to above. I just had an HM series giving me fits with a random/racing idle, PO torqued/twisted the governor mount on the shaft, even gov adjusted properly didn't fix, had to swap in another gov assy...translation, check gov adjustment. The little passages for the idle circuit get plugged easily too.

I cleaned those idle circuit holes. I will check the throttle plate too. Gov serms to be adjusted correctly. Watched many you tube videos on all this stuff!

 

[markus]

Throttle shafts also wear excessively If they are worn out you will get an erratic idle since it both sucks air and does not allow the butterfly to seat where it should in the bore.

First pic I could find from one of my builds/carb conversions that shows some of the shafts, a "good" shaft it located top left, the worn shaft that it replaced is shown on the right side jsut above the well used vise grip holding the removed primer nipple, you can see where they wear out riding against the upper hole in the carb body.

I retrofit foam seals onto them a lot of times as well for a little more seal and lubrication abilities (better if using a later steel throttle shaft since it will wear aluminum body more) , you do have to modify the cast in return spring stop on the older carbs when doing that retrofit usually though so it cant slip up off the nub.