Hitachi 24eap won't idle. will run if you use the throttle trigger.

Try disconnecting the throttle cable at the carburetor and see if idle remains high. (I) want you to isolate issue to the new cable installation only and not a combination of cable and other.

I believe the handle/trigger position is critical to throttle so be sure the distance of the trigger to body of unit has not increased.

Comment below and I assist further if need be.

Check the Hitachi web site where they will show you where to look.

This machine has a metal throttle rod from the trigger to the carb, you need to look at the side of the carb where the rod connects to the carb, with your finger ( with the engine stopped ) work the carb throttle spindle manually to see if it is moving freely and it springs back to the small throttle idle screw easily, if it does unscrew the idle screw with a cross head screw driver until the machine idles ok, if not you need to take the l/h side cover off to investigate what has happened .

The KM90 is a 4mix engine that has valves. You may need to check the valve clearance, using the clearance tool.

why play with it dump out the fuel and bring it back

Check the owners manual for the location of the idle screws. There should be two (low/high). After starting the saw, use a small screwdriver to turn the screw counterclockwise until the proper idle speed is reached. These screws are usually recessed in the housing on the left side of the saw, and may have an L and an H next to the holes. Be careful, as sometimes these are plastic screws and you don't want to strip them. Note the original position by looking into the hole so you have a starting reference point. If the screws have no effect on the idle, you may have a throttle linkage problem (if the saw will only run at high speed and the throttle trigger has no effect). Your goal is to have an idle speed that won't kill the engine but will also keep the chain from moving or creeping on the guide.

Open the carburetor area cover and remove the air cleaner so that you can observe the throttle arm and the idle speed screw which stops throttle movement to set idle speed. If the throttle arm doesn't come back completely to the screw, then likely, the throttle trigger is jammed with sawdust/dirt that prevents the throttle arm from returning. Disassemble the trigger assembly making notes of part placement as you go. You will usually find a plug of sawdust in the trigger mechanism. Recheck the throttle arm motion after putting the trigger back together. You may have to advance the idle speed screw several turns CW to be able to keep the engine running when the throttle works correctly. Idle speed should be set so that the engine continues to run, but the chain doesn't try to turn. Hope this helps!

Expose the carburetor so that you can observe the action of the throttle lever on the carburetor. The trigger should move the lever from the idle adjust screw to full throttle stop. If no movement observed, remove the trigger assembly from the front handle (make notes as you remove the pieces) and clean the area of sawdust/dirt accumulation. Recheck the action after everything is re-assembled before starting the engine. If the idle speed is still excessive, then turn the idle speed screw several turns CCW until the chain stops turning. Try wiggling the carburetor body to see if it has come loose from the engine. Hope some of this helps!

Open the cover over the air cleaner so that you can observe the action of the throttle cable and carburetor lever. Operate the throttle--normal action is lever wide open at full throttle and lever resting on idle stop screw when throttle released. If action is restricted, disassemble the handle where the throttle trigger is located and clean out the sawdust. Recheck throttle action. The throttle cable shouldn't require lubrication. Clean the air filter and check the operation of the engine. Hope this helps!

Remove the air cleaner assembly so that you can see the action of the throttle mechanism. If nothing around the carburetor throttle arm is broken or out of place (the return spring), then remove the screws in the throttle trigger part of the handle and look for sawdust blocking throttle trigger action. Hope this helps!