How to adjust the LA screw a Stihl 290

Bearridge

New member
HI guys, I'm new here and was wondering if anyone can help me.
I messed up! Lol
My chain continued to spin at idle so I tried to fix it by adjusting the LA screw. Well now I can't start the saw.
I got lost as to where I was when it was running.
Can anyone give me some advise as to how many turns of the LA screw in or out to get close to starting?

Thank you for your help!
Bearridge
 

Bob Hedgecutter

Moderator
Staff member
If the chain continues to spin at idle and turning the idle (LA) screw fails to improve matters- odds are it is not carb related and can be weak clutch springs or a massive air leak.
The fact your saw now will not start suggests the latter- pull the muffler and check the piston through the exhaust post to see if it is all torn up.

The LA screw is not set by a number of turns in or out- most Stihl manuals will list a certain RPM (set via tachometer) to set the screw for (pre the RPM needed to engage the clutch) then tune the low circuit and return to fine tune the LA to a point where the chain stops rotating.
 

Bearridge

New member
If the chain continues to spin at idle and turning the idle (LA) screw fails to improve matters- odds are it is not carb related and can be weak clutch springs or a massive air leak.
The fact your saw now will not start suggests the latter- pull the muffler and check the piston through the exhaust post to see if it is all torn up.

The LA screw is not set by a number of turns in or out- most Stihl manuals will list a certain RPM (set via tachometer) to set the screw for (pre the RPM needed to engage the clutch) then tune the low circuit and return to fine tune the LA to a point where the chain stops rotating.
 
Last edited:

Bearridge

New member
Hi Bob thanks for the reply. My saw ran perfect until I decided to try and adjust the chain moving at idle.
I just want to get it started again. Then go from there as to why my chain spins at idle.
My clutch springs seem fine and I cleaned the inside of my clutch disc.
I'd like to know about how many turns should I back my LA adjustment from completely closed to get started.
Then I can go a 1/4 turn either way until I can get it started.

Thank you!
 

Bob Hedgecutter

Moderator
Staff member
Hi Bob thanks for the reply. My saw ran perfect until I decided to try and adjust the chain moving at idle.
I just want to get it started again. Then go from there as to why my chain spins at idle.
My clutch springs seem fine and I cleaned the inside of my clutch disc.
I'd like to know about how many turns should I back my LA adjustment from completely closed to get started.
Then I can go a 1/4 turn either way until I can get it started.

Thank you!

The LA does NOT have a turns out setting- but the L does if you have been messing with those as well?
Set your L screw one and 1/4 turns anti clockwise (out) from lightly bottomed fully in (clockwise)

The LA can be anywhere in its range from fully seated to where it is not bearing on the throttle plate- the saw will run and start- the chain may be tearing around the bar- but it will start. The LA screw only alters the amount the throttle plate is adjusted to to alter revolutions and has no bearing on the fuel/air mixture reaching the combustion chamber as such- it is not a jet- it is a permanent throttle applicator.
 

Bearridge

New member
The LA does NOT have a turns out setting- but the L does if you have been messing with those as well?
Set your L screw one and 1/4 turns anti clockwise (out) from lightly bottomed fully in (clockwise)

The LA can be anywhere in its range from fully seated to where it is not bearing on the throttle plate- the saw will run and start- the chain may be tearing around the bar- but it will start. The LA screw only alters the amount the throttle plate is adjusted to to alter revolutions and has no bearing on the fuel/air mixture reaching the combustion chamber as such- it is not a jet- it is a permanent throttle applicator.
Ok Bob thank you. I did not touch the other adjustments. So by me messing with just the LA screw, it should start at any setting and I should be looking elsewhere for the reason its not starting?
 

Bob Hedgecutter

Moderator
Staff member
Ok Bob thank you. I did not touch the other adjustments. So by me messing with just the LA screw, it should start at any setting and I should be looking elsewhere for the reason its not starting?

Take the filter cover and air filter off so you can see the screws and what they do- where they go.
Screw your LA screw so the throttle plate is sitting about central on the tapered cone- try starting from there.

Getting back to the racing chain you were trying to cure- air leak and or clutch springs are number one causes for that, then the saw stops running due to low compression from being run lean.
Take the muffler off and look at the piston- 5 minute job that can show you a lot of answers as to why it does not run- may be nothing to do with altering the LA screw.
 

Tyy

Member
You have not mentioned the manf , model of saw . A abnormal high idle , that the idle screw cannot lower , could also be a bad seal . However since it will not start , set your low speed jet at 1-1/4 out from gently seated . It should fire or at least burp. The inlet needle valve may also be restricted . You would have to remove the diaphragm to check that its free . Some models have a small inlet valve prefilter screen , may be fouled. Final inspection would be to ensure your fuel tank filter is clean . Anyhow good luck , get back to us !
 

Bob Hedgecutter

Moderator
Staff member
You have not mentioned the manf , model of saw . A abnormal high idle , that the idle screw cannot lower , could also be a bad seal . However since it will not start , set your low speed jet at 1-1/4 out from gently seated . It should fire or at least burp. The inlet needle valve may also be restricted . You would have to remove the diaphragm to check that its free . Some models have a small inlet valve prefilter screen , may be fouled. Final inspection would be to ensure your fuel tank filter is clean . Anyhow good luck , get back to us !

Have a read of the thread title- you can add an MS between the Stihl and 290 if you like, but that will give you a hint at the make and model in question. ;)
 

Tyy

Member
Have a read of the thread title- you can add an MS between the Stihl and 290 if you like, but that will give you a hint at the make and model in question. ;)
Thanks Bob , yep got it . So yep , everything I mentioned is very pertinent to the good old MS-290 Stihl's . P.S. You could spray some map gas or propane around the clutch sprocket once running also to see if the high idle changes which would indicate or verify the air leak . ;)
 

Bearridge

New member
Take the filter cover and air filter off so you can see the screws and what they do- where they go.
Screw your LA screw so the throttle plate is sitting about central on the tapered cone- try starting from there.

Getting back to the racing chain you were trying to cure- air leak and or clutch springs are number one causes for that, then the saw stops running due to low compression from being run lean.
Take the muffler off and look at the piston- 5 minute job that can show you a lot of answers as to why it does not run- may be nothing to do with altering the LA screw.
Thank you Bob and Tyy for your help. The saw is running and I have stopped the chain from moving at Idle. Knowing what was said about the LA screw, that the saw should run at any setting in its range made me think I must have just flooded it. Because I got it started the following day. It started right up.
Thanks again!
 
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