Cold cutting

[SasquatchMan]

I was cutting at about -10 C the other day, and my saw seemed to have a little hesitation when I pulled full throttle.  Idle seemed fine, and starting was n.p.  Is this just a cold weather thing, or should a guy turn up the low idle screw a bit?

[Kevin]

Does a guy have cold weather adjustments at the air intake?

[Minnesota_boy]

That hesitation on acceleration suggests that the idle is a bit lean.  If you have the cold weather adjustment that Kevin mentioned, try that first.  If that fails or the saw doesn't have it, try opening the low speed mixture about 1/8 turn.  Shouldn't take more than that.

[SasquatchMan]

Yeah, I've got the saw set up for cold operation - it's a Stihl 290 with the little airflow plate etc...  The saw ordinarily runs perfectly, and I ran it long enough that it was warm for sure - I cut for about an hour.  My suspicion is that the low speed needs a wee tweak for the real cold.

[Kevin]

Have we checked the muffler lately?
Do we have a tachometer?

[SasquatchMan]

Kevin, we haven't either, but a tach could be rustled up, and the muffler honestly doesn't have enough hours on it to be a concern (or if it is, I have some major malfunction).

The saw functioned fine - really perfect at idle (it idled just right (hopped around and sounded crappy) while I moved some sticks) and at speed - but there was just this slight hesitation when I pulled the trigger.

What would I be checking with said tac?

[Kevin]

I would check the idle speed and the high speed.
It could be a number of things.
If the air filter is clean and the muffler and screen look good I would check the rpm.

[jokers]

+
SasquatchMan

Kevin is telling you in a round about way that using a tach is checking your air/fuel ratios which are significantly and adversely affected by air as cold as -10°C, compared to the temps that you have had the saw previously adjusted to run in.

I believe that you said that this saw is relatively new to you so I am assuming that you weren`t running it last winter. Also consider that the vast majority of saws delivered these days are also running right on the hairy edge of leaness out of the shop. If you were running on the lean side during the warmer summer temps, what do you suppose is going to happen now that the air density is way up due to coldness? It really leans you out.

I don`t even mess with the winter flaps unless I`m using the powerhead in fluffy or blowing snow. The flaps are just a Band Aid attempt to correct the problem without really addressing the problem of significant changes in air density at different temps.

Take your saw to your dealer and have him show you how to tune it, or at the very least, have him tach tune it and make note of what the engine sounds like out of the cut so that you can approximate this tuning in differing temps.

Fine tuning the air/fuel ratio, in small increments as Minnesota_Boy pointed, out should fix your problem. Remember that turning the screws in leans the mixture and out richens the mixture and that the lo speed screw has an effect on the hi speed mixture but the hi speed screw has no effect on the lo speed mixture. You may also need to tweak your idle speed screw. Try everything in moderation, listen to the engine while giving it enough time to respond to changes, then try it in a cut.

Russ

[SasquatchMan]

Russ and Kevin, I guess that's what I was hoping to avoid - the weather here goes up and down all over the place = could be -30 next week (doubt I'd be out cutting!) or it could be +15.  I really don't want to get into a situation where I have to adjust my saw every time I take it out of the box...  I'm just about due for a chat with my dealer anyhow, so I'll see what he recomends in terms of setup.

These saws come from the factory with the H screw set all the way off of lean so I can't really richen that side of things except as you say, with the L screw.  

Kevin, I'm pretty sure the idle speed is just right - the saw sounds the same as always, chain isn't running, but I'll maybe find a tach and make sure - I think the manual specifies 2500 rpm

I can live with this hesitation as long as it isn't indicative that the saw is going to malfunction in a year or two because the mix is wrong....

[Kevin]

Squatch;
If you can't get your mitts on a tach, you can adjust the low speed needle until the engine accelerates without hesitation.
Adjust the idle speed just below clutch engagement.
As always, when in doubt ....have the dealer check it out.

[jokers]

The movement or adjustability of the screws is limited by, err, ah,.... limiters that can be removed and then be reinstalled in a different position allowing a limited range of motion from where you have repositioned the screws from your initial fine tuning. These limiters are not the same thing as a fixed jet which is total junk in my not so humble opinion.

The average Stihl being shipped to anywhere in North America from Virginia Beach is going to be set up lean for anywhere else above sea level, right from the factory. Given that the average dealer of any brand of chainsaw is no longer a two stroke expert or has people who don`t care working for them(typical American service sector job mentality), your saw is not going to be set up right when it leaves the dealer. I don`t care what Stihl says, you aren`t getting full service from the average dealer. Most times, if the saw is adjusted at all, it`s simply adjusted within the range of the limiters and left at that. You may need to remove the limiters and fine tune the saw yourself.

You don`t need to worry about having to adjust your saw daily based on temperature or atmospheric pressure. You can get a "good enough" adjustment by tuning it optimally for the coldest temps and it will be slightly rich when it`s warmer. Slightly rich at the carb is preferrable to slightly lean.

Russ

[jokers]

BTW, just wanted to point out that the idle speed is a mechanical carb adjustment and has nothing to do with proper fuel/air ratio.

Russ

[Kevin]

The problem I see with fooling with the  limiters is making adjustments to the carb when it might be affected by another problem unrelated to a carb adjustment.
You end up trying to compensate for another problem by adjusting the carb out of limits which might result in making the situation worse resulting in a damaged saw.

[jokers]

Good point Kevin, just that it totally discounts the condition that I have found nearly every new saw I`ve seen in the last few years to be in. Screws stopped at the limiters and the carb out of adjustment. Then again, your advice is the most prudent to follow until satisfied otherwise. I merely wanted to point out that the limiters are removable and often require being removed for adjustment, then being reinstalled with the screw at the midpoint of the limiters range.

Russ

[SasquatchMan]

Thanks guys - I'll see what I can do - I'm at pretty high altitude, so hopefully the factory leanness is cancelled out?

Either way, I'll run the saw again (it's minus 17 now) and see if I can diddle a bit more low end in... I'm sure I can get a tach to get the proper high setting too - Those saws are supposed to max out at 10000, right?

[Bobcat_pa]

Geography=Pennsylvania)   Went through this problem with both Stihl and Husky saws.   With the Stihl, it was perfect June to Sept, put it on the shelf until Nov, and had to set the idle richer.   I bought this new Husky 353 in Aug, and starting to see the same problem in late October .    My question is where can you read some indept material on tuning your chain saw ?  I want to learn how to adjust, but like most people I do not want to get a "reputation" .   My "cutting season"  varies 80 degrees from winter to summer.   I just purchased the "better" tach from Madsens and gave it a little test.   But, where do you go from here ?   Just like SAS...,  I want my equip to run properly and no self-abuse.    
bob

[Kevin]

13,000 for high speed no load on the 029.

Bob;
Check your manual for high and low rpm.
Make sure your saw is clean and follow the procedure outlined in your manual.
If you can't get the proper rpm with the tach, chances are you have another problem that requires some attention.
Be accurate with your fuel mix also, keep it fresh and constant.

[jokers]

Hey Sasquatch

You caught me talking out my butt on the correlation between lean from the factory saws and Virginia Beach. That`s what I get for trying to put two otherwise lucid thoughts together. I should have stated that the saws being tuned for Va Beach are tuned lean and mistuned for everywhere else, apparently even at elevation.

Tach tuning is supposed to be a fool proof method if your saw has no air leaks and is otherwise sound. With the limitation of having a high speed tuned mostly for low emissions rather than max power, tach tuning will get you where you want to be. You will probably find that your saw cuts quicker if you tune max rpm somewhere between 300 - 500 less than factory spec, hence a richer fuel/air ratio.

I don`t want to step on any toes and point anyone to a different forum. Let it suffice to say that this topic is covered in depth a few other places on the net. A Google search might help or you could go to Madsen`s site and read their tutorial and listen to their wav of a properly tuned two stroke. Just be sure that you fully comprehend what they are telling you before you start tweaking.

Russ

[Kevin]

I don`t want to step on any toes and point anyone to a different forum.
Russ

Russ;
No problem pointing, some leave but the good ones always come back.  

[SasquatchMan]

Geez Kevin, I can't tell if ya want me back or not???