One engine startsand you move throttle to run, engine runs at extreme rpm's and will not throttle down

adjust the carb to governor linkage

You should have two adjustments, lo and hi speed. Maybe even a third mechanical adjusting screw that just sets the idle higher by moving the throttle plate open or closed.

Adjust the high speed first to attain the desired 'no-load' rpm which SHOULD NOT be the highest rpm you can get. If you adjust it on the high adjustment to where it screams but 'blubbers' at wide open throttle you are near to where it should be. The blubbering will straighten out under load and cause the motor to run at full power. If you mistakenly adjust it to full rpm in no-load condition, it will be set 'too lean' to safely run the saw. The excess heat generated from the extremely lean condition could either score the piston and cylinder wall or melt a hole in the center of the piston.

Then proceed to adjust the lo setting. Adjust it to where the chain just begins to rotate, then adjust it back to where the chain stops.

Check movement of the governor arm without it running. You should be able to move it by hand. If it is stuck, it could be the idle solenoid, or possibly something else more major.

Running lean on the pilot
Air leak after the carbs
Loose clamps
Stuck throttle cable
Wrongly routed cable
As above with choke

The most common issue is the spark plug boot shorts to the engine.

You could have a dirty EGR valve, you can re move it from the manifold and clean it with Throttle body cleaner. Might as well buy two cans, since your cleaning the EGR, might as well clean out the throttle body too.
Spray the throttle body cleaner in to the throttle body with the engine running and try to keep it at 1000 rpm and then to 1500 rpm as you clean out the throttle body and let it idle down for 2 min then turn the engine off. Then turn the engine to the run position for 10 seconds and start and let idle, ro for a test drive and hope that solved the problem, if not there a few more things we can do which will consist for tune up.
Note: Clean the EGR first so you don't burn your self since the engine would still be cool before you clean the Throttle body.
Good luck and keep me posted.

Not many reason for this......One: your throttle is stuck open (I'm sure you would have found by now)..If not.... Its an air leak between the carb and intake port. The only purpose the carb. serves is to regulate air/fuel mixture and also the rate in which both fuel and air enters the motor thus maintaining consistent RPM stability while at idle all the way through to WOT (wide open throttle) when in operating....The Throttle body has a foil inside which opens and closes allowing air into the motor. The foil opens when throttle (lever/trigger) is applied and allows the air in that is needed to acheive appropriate RPM and power or to lower RPM when not needed. All engines WANT to RUN and the only thing stopping them from running away is the restriction of airflow....So if there is a leak between the Carb and the Intake port, then Carb will then be bypassed and the engine will **** in all the air that it is mechanically capable of through the path of least resistance, unregulated...... This is also extremely harmful to the motor because a "lean" fuel/air mixuture is caused meaning it is drawing in more air and less fuel which causes increased thermal combustion temps. and can burn a hole through pistons

check idle speed control make your throttle valves not stuck.check for vacuum leak around the throttle body area look for broke gasket.

hi it sounds like an air leak on the inlet manifold side or a faulty idle valve which sucks air in when it shouldn,t checkall the hoses round the manifold first and listen to see if you can hear air beening sucked in when you turn the a/c on it connects the clutch on the pump which is run off the engine and slows the engine down slightly yates210456