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Re: how do you set the mixture screws
I'd start at 1.5 turns CCW from lightly seated. Then tune for performance. It is probably fitted with tamper resistant fittings mandated by the EPA. I contact my local Stihl dealer when my saw needs adjustment. HTH
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Set both the high and low mixture settings two full turns back from the closed setting(full clockwise).. Set idle speed for all ahead full.
Start sucker and after a warmup throttle it down and then start adjusting the low mixture screw for fastest idle. Then lower idle some more but not to point where it starts to run rough. Then rev the sucker to high speed and adjust the high mixture for max speed. You may have to make a slight adjustment on the high speed to get a smooth transition from low speed to high.
Start with 1 full turn out from the closed position on both the idle and high speed mixture screws. After the engine has warmed up, hold the throttle wide open and adjust the high speed mixture screw until the engine runs at the highest RPM then turn the screw counter-clockwise about 1/8 turn.
Next, turn the low speed mixture screw in whichever position gives the best idle.
After making these adjustments, check the throttle response. If the engine hesitates when applying the throttle, turn the low speed mixture screw counter-clockwise about 1/8 turn.
If the two screws are side by side, one is the high speed mixture screw and the other is the low speed mixture screw. To set the high and low adjustment screws, tighten the screws in until they stop, don't force the screw after it stops. Back each screw out 1 1/2 turns. The engine will start and run here if everything else is ok. Fine tune each adjustment screw by closing the screw off (CW) until the engine runs rough. Back the screw out (CCW) until the engine smooths out. Run the engine at full speed and adjust the high screw. Let off the trigger and adjust the low screw. Once the mixture screws are adjusted, you can turn the idle screw to adjust the idle speed. It can take some time getting it all adjusted.
Not knowing the model, you can always look on the body of the carburetor, there should be an "H" for the high speed mixture screw and an "L" for the low speed or idle mixture screw. Both screws should be set initially 1 to 1 1/2 turns out from seat and then the carb. will have to be fine tuned from there. The high speed screw is adjusted when the throttle is in fast position, at 1 1/2 turns out you should have a slightly rich mixture so you may need to slowly turn it in until you hear the saw's rpms start to increase. You want to find a medium point between too rich and too lean. The low speed or idle mixture screw is set the same way just at idle rpm instead of full throttle, find a medium between too rich and too lean. You should be able to throttle form idle to wide open without any "lag" or "stumbling". You can also offset any rpm change at idle with the idle speed screw (not to be confused with the idle mixture screw). Hope this helps.
If its an old Homelite you should have 3 screw on the carburator.
First bigger screw for adjust idle on the butterfly.
The 2 other for the mixture. One screw is ''L'' for low rpm mixture an other screw is ''H'' for high rpm mixture.
First the idle screw. It should just open a little bit the carburator butterfly.
Second full close both ''L'' and ''H'' screws (turn clockwise).
After open both ''L'' and ''H'' screws 1/2 to 3/4 turn (conterclockwise)
Normally the saw should start. Tune the ''L'' screw to have the motor running at idle if idle is to fast at this point is not important. After motor is running by itself at idle tune the ''H'' screw.
Full throttle tune the ''H'' screw to be able to pass from low rpm to high rpm with no lag.
Than at full throttle open again a little bit the ''H'' screw to make the high rmp mixture more rich.
Becarful if ''H'' screw is not adjust correctly the mixture will be to poor and motor damage can occur.
It may be necessary to re-tune a very little bit the ''L'' screw and idle screw after the correct setting of the ''H'' screw.
If it still not working carburator kit may be needed,
On some newer model there is no adjusting screws in this case see if a carburator kit is available for your model.
The high speed mixture screw is initially set at 1 & 1/2 turns out. Then adjust it to give good acceleration and top speed, while not closing the screw more than you need to. The low speed mixture screw is set at 3/4 of a turn out. Adjust that, to give a smooth idle. The 3rd screw, the idle speed screw, is set to give a low idle speed without stalling.
You need to get your mixtures right. It is probably running to lean. wind your low mixture screws in counting every half turn as you go so you can remember the factory settings (ex. L 1 & quarter turns, H 1 & half turns). Then wind them back out, winding the low mixture out a lil further (eigth of a turn) while running, rev it a bit, try a cut with it, then wind the High mixture screw out a bit if it hasnt improved. You will eventually stumble on the right mixture for the weather conditions.
>>The Following is the Instruction File for Setting the Air Mixture Screws. Any Input is Appreciated. The Procedure is the Same for 1 or 2 Mixture Screws, Just Use the Instruction File and Skip Over the Section with the Missing Mixture Screw ( Usually the H Mixture Screw). >>Now Setting the Air Mixture Screws: >>****Turn the Idle Air (L) and Main Air (H) Mixture Screws In Until SNUG **Do Not Jam** Then Reverse Both Screws 1 1/2 Turns. Set the Throttle Full Open, Start the Engine. >>Turn the Main Air (H) Mixture Screw Clockwise Until Proper Revs are Obtained. **Carefully Use your Finger and Move the Governor Arm to Rev the Engine (on Chainsaws and Trimmers Use the Trigger to Rev the Engine) Until you Reach Max RPMs (on Chainsaws and Trimmers, the RPMs are Not Set to MAX. Set to Max and then Reverse the Setting Screw 1/4 or 1/2 Turn. If the H Mixture Screw is Set too High; the Engine will be Starved for the Oil in the Gas and Damage the Piston and Jug/Cylinder) and the Engine is Running Proper at Full Throttle Up a Grade and for Chainsaws and Trimmers they Do Not Bog DOwn Under a Load. Occasionally you May have to Turn this Counter Clockwise to Achieve the Proper Revs.** >>Now Allow the Engine to Idle. Set the Engine Idle Screw (Not Idle Air) so the Engine will Stay Running if Required. >>Now Set the Idle Air (L) Mixture Screw so there is No Hesitation when Rapidly Throttling from Idle to Full Throttle. Reset the Engine Idle if Required.****
Please, Do Not Hesitate, If I Missed Something or you Hit a Snag or this Does Not Correct the Problem, I am Here if You Require More Assistance. Hope this Helps. Let me Know What Happens, Please. May the All Mighty Bless You and Yours. Be Safe and Be Happy. Thanks.