Howdy people, Was running 1/2 - 2/3 throttle when engine or exaust went poof. Machine slowed & was not running on stop. Cranked up & it idles fine with no distress but cannot advance throttle without stalling motor. Will not move from tracks. Changed brain & no difference. I am wondering if a head gasket is blowed. Just a thought no proof. Appreciate any ideas.
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the sequence to throttle adjustment is to adjust to high speed first ( screw closest to the air filter) turn in in or out until it fires evenly at rpm and picks up rpm easily
now hold the throttle at full throttle and slowly idle down while adjusting the idle screw ( closest to the butterfly) to maintain engine running
the screw should have been turned all the way in then back out 1 1/2 turns before starting the engine
keep slowing the engine while making very small adjustment until it idles at rpm slow enough that the chain is not driving
If you get it low but it stalls out , then adjust the throttle stop screw to maintain idle rpm
Correct adjustment is from this point the rpm increases rapidly with out falter ( fine tune high speed screw to achieve that)
and when left to idle will do so evenly without driving the chain
all of this working is depending on the carby having new diaphragms , needle height adjustment correct and the system cleaned out
Screw in the HIGH and LOW needle valves. Then turn each one out 1 full turn, That should be a good starting point.
After engine is running Run engine at Full throttle. Loosen HIGH screw until the engines RPM slows a bit. When that happens Turn screw back in until it revs high and then just starts to slow again. You do not want the engine to run at it's highest RPM or it's not getting enough Lubrication It need to run Rich, that's why you screw the screw in a bit after the engine has reached it's highest RPM. Let it idle down . Then Accelerate hard, if it hesitates, loosen or tighten the LOW until it accelerates quickly with no hesitation.
if the engine is in good shape..screw in both carb jets adjusting screws till they seat lightly, then back them out 1 1/2 turns, srew in the throttle adj screw a turn and start the motor,,warning if the chain is on make sure the blade isnt likely to touch anything when the engine starts as you will have to have the brake off to get started and adjusted. With the engine running, adjust the throttle srew until it is idling just above shutting off speed, then adjust the "L" low speed jet to get the best idling speed without srewing it in much, reset the throttle srew, then , while trying to accelerate suddenly each time, open the Low jet a little at a time until the machine accelerates smoothly without hesitation. Reset the throttle srew to a position that the chain stops running at idle and check again that the acceleration is without hesitation ( usually with "L" jet about 1/4 turn out more than best idling). The high "H" jet can now be set to give the best power while cutting a block of wood.
I just saw this deal on the Fs200 Stihl Brushcutter. Equipped with a Zama c1qs51 carb. Junk the carb. Go to a stihl dealer and buy a three screw chainsaw type carb with a high low and idle screw. The c1qs51 is junk.The three school carb will put an end to your worries. Of course change your fuel filter naturally. I guarantee this will fix the thing. I own an Fs200 and Fs250.
The first place I would look is the IAC motor (idle air control) usaully on throttle body and possibly dirty throttle body and one last thing could possibley be EGR valve exaust gas recir. as if it stuck open it will lean out engine.
Use compressed air to blow the sawdust and dirt out from the cylinder and head. Clean the screen in the muffler. Make sure that the fuel/oil ratio is correct. Turn both L and H screws in the carburetor CW until lightly seated, then back out 1-1/2 turns CCW each. Start the engine and allow to warm up. Open the throttle and turn the H needle CW until the engine starts to speed up, but is 4-stroking. The correct position is when the engine 4-strokes unloaded, but immediately 2-strokes when cutting is started. Let idle and adjust L CW until the engine runs fairly smoothly, yet allows the engine to 'follow the throttle' as you accelerate it. Set the idle speed screw so that the engine keeps running, but doesn't try to move the chain. Hope this helps!
If there is spark and the sensor is in position and secure. There is a cold idle valve beneath the throttle body. It should repeatedly click as it actuates on and off.. Theory is it creates a controlled vacuum leak until the engine can carry ttself once warmed up.. Good Luck