High Idle
#1 the governor arm will not pull back all the way, or the rod connecting the carb to governor arm is not hooked up correctly in the right holes.. (OR BEEN MODIFIED and too short) There is a small 1/4 hex screw in the base of the governor arm that you can loosen and rotate the arm around to adjust where it is located.. I've noticed when they are right, the arm actually tips out towards the crankshaft side of the motor, probably 10 to 15 degrees off from strait from the small square base the governor arm attaches to..
( I think I had this correct, but I disconnected-and removed the governer arm completely for this exercise to isolate problems.)
#2 and probably even MORE likely.... is your butterfly is not attached to the throttle shaft correctly.... There is a timing mark on the butterfly.. That mark should be dead nuts perfectly true with the rod... The butterfly is oblonged to fill the round hole as it sets at an angle closed off... THEN the butterfly has to be bolted to the shaft SIDE TO SIDE correctly too.. A lot of the times the screw is off centered in the hole one side or the other to make it all close up right.....
You SHOULD be able to pull the throttle to CLOSED and have the carburetor shut COMPLETELY OFF.... NO!!!! NONE NOT ANY!!! air or day light coming past the butterfly when it shut completely off..
If it's out of round, off centered, worn out... It will create an air leak and not seal.. Best way I've found to get one right is make sure your timing mark is dead nuts true and barely SNUG The screw down.. hardly at all.. JUST enough to hold the throttle shaft and butterfly as one piece.... Then close the throttle with the idle screw completely OUT off the carb.... If it will not close off COMPLETELY!!! what I will do is turn it wide open then turn it wide SHUT again with a little bit of force... not a LOT enough to BREAK OR BEND anything... but a little gentle force... Just repeat that process a couple dozen times real quick... Eventually that butterly slamming shut in the round hole... will align the butterfly WITH the hole... and it should close off completely sealed off....
(I did not double check this, yet, because:
1.I did not disassemble the throttle shaft/butterfly when I rebuilt the carb.
2.After I had everything put to gether I did not want to have to take everything apart completely.(this thang is all custom built and cramped in)
3.I fiddled with the carb alot rebuilding it and I think it is closing off completely.
SO theres those two things to look for as well... ALSO the carb may just be worn out at the throttle shaft and is leaking air there too...
I would say do like DMR said and check for air leaks at all of the gaskets first, turn the idle screw down as far as it will go until it stops even MAKING contact with the throttle plate... If all that fails, take the carb off, check to make sure the butterfly will close off completely, the put the carb back on WITHOUT the governor setup atached... THAT WAY you know it is YOU VERSES THE CARB.. and NO governor or throttle parts interfering... If the carb is all alone bolted to engine with the idle adjustment screw completely removed from the carb and it STILL refuses to idle down....You have an air leak somewhere....
Get us some pictures of your setup...
