Stihl : MS170 & MS260 Choke Adjustment

[Jack_Shaft]

Just finished rebuilding a couple of Stihl saws, I have been able to get the LA and HA as well as idle adjustment all figured out and the saws start really well under full choke, but when the choke goes back to 1/2 way open for warm-up, both saws really rev up high and I'm afraid that it's not good for the engines when they're cold. I know that the MS260 is a little different since the choke is built into the air filter.

How can I adjust the choke independently from these measurements? Linkage? Some other adjustment screw?

-Rob

 

[skwerl]

Can't really offer much more than this:
http://www.madsens1.com/sawtune.htm

I have no idea how to answer your question because it doesn't make sense to me. Adjust the carbs like the link says and you will be golden.

You know that the limiter caps must be removed in order to get the adjustment correct, right?

 

[sedanman]

There is no half choke position on those Stihls, There is a high idle position but the choke is either ON or OFF no in between.

 

[Jack_Shaft]

There is no half choke position on those Stihls, There is a high idle position but the choke is either ON or OFF no in between.

No idea here.

There is definitely a full-on and a half-on position according to the diagrams on the rear case. All the way down is full choke (how you start the unit), as soon as it fires up the lever pops up one notch to the half-choke position (i.e. |/| symbol) then once you touch the throttle, the lever pops up one more notch to the "ON" position. One more notch upwards and the lever is then in the "OFF" position.

Does this sound familiar? Perhaps our Canadian saws are different?

 

[Jack_Shaft]

You know that the limiter caps must be removed in order to get the adjustment correct, right?

Limiter caps? All of the adjustment screws appear to turn well as-is.

 

[Jack_Shaft]

There is no half choke position on those Stihls, There is a high idle position but the choke is either ON or OFF no in between.

Perhaps the half-choke I am referring to is really the high idle.

I don't understand why the saw would run spot-on at idle when the lever is in the "ON" position, while at the same time the thing revs really high (like 1/3 throttle high!) when the lever is in the high-idle position?!?! I figured the two would be related.

 

[Lakeside53]

it is and they are... when the choke is on the high idle is selected - helps starting. The throttle linkage is just advances a tad, opening the butterfly a little. The fast idle is for a warm start without the choke. Click the throttle, and the saw immediately jumps to normal idle. All modern stihlss are the basically the same.

 

[Lakeside53]

You know that the limiter caps must be removed in order to get the adjustment correct, right?

There are no limiter caps on the MS260...

 

[skwerl]

Stihl got rid of the limiter caps??? How'd they manage that? The last 026 I owned had a fixed high speed jet (POS, PITA) and pretty much turned me off to Stihl for the time being.

 

[Lakeside53]

Stihl got rid of the limiter caps??? How'd they manage that? The last 026 I owned had a fixed high speed jet (POS, PITA) and pretty much turned me off to Stihl for the time being.

They never had limiter caps on the 260... the carb was either the WT403 with no high screw, or the 426 (and a few others) with a semi-fixed high jet and a H screw - but you only get to vary about 10-15% of the gas flow which is usually enough.

I fix a lot of 026 / 260 and although my hand twitters toward the box of WT194 or WT 426 (2 adjustment screws) I'm surprised by how well the WT403 works for those that don't want (or need to want) the perfect H adjustment. It runs a tad rich, but usually Tach at 13,000+/- which is plenty for guys with a factory muffler and who want to cut wood without a stopwatch

On the other hand, I've sold a lot of WT194 / WT426 to AS members... (I'm OUT OF STOCK right now).

 

[Jack_Shaft]

As a final resolve I went to see my dealer, he just told me it was normal for the MS260 to go quite fast on high idle and instructed me to just switch back and forth between high idle and just the regular "ON" position while warming up, instead of running the saw fast & cold under high idle.

Worked for me, saw works great anyway, it was just a start-up issue.

Thanks for all of the help.

-Rob

 

[buck futter]

In the owners manuals it says to blip the throttle off fast idle as soon as you can, Some times the saw needs a little throttle when cold to keep running so I will leave mine on fast idle for about 15-45 seconds. My husky will not continue to run when cold unless the choke is pulled out a little until it is warmed up but runs fine after, I think it needs a little more gas on the low, but I'm still messing with getting it set up. But you didn't mention it stalling on a cold start so it is more than likely normal.


Lucky