Tuning chainsaw for freehand milling (running at half-throttle)

[charles chang]

i know some of the points were discussed in this thread: https://forestryforum.com/board/index.php?topic=111637.0, where the OP's chainsaw pistons seemed to have been damaged by running his saw at half-throttle while doing carving work.

many suggested a richer oil mix (40:1, 32:1, etc), adjusting the carb to run rich, taking breaks to prevent overheating, and giving full throttle here and there.

i'm running 372xp, and in my first year owning the saw (my first chainsaw), blew out the pistons.  i was freehand milling, running at around half throttle.  i was using 50:1 mix (stihl oil mix), milling at around 90 degrees weather, all day long, for days straight.  i remember the saw smoking.  it definitely overheated.  back then i didn't really pay attention to the sound of the throttle (running lean), nor did it know how to adjust the carb.

i've since then started using husqvarna synthetic oil, at 40:1 mix, and adjusted carb to run rich, and removed the spark arrestor.  i'm starting to freehand mill again, and just want to make sure my saw is tuned at its optimal for running mostly at half-throttle.

do you guys have any other tips?  i've kept the limiters on my carb, but i'm open to removing them and running the saw richer, and i'd be fine with replacing spark plugs more often since they're cheap.  i'm also open to trying 32:1 mix.  

many videos of eastern asian freehand milling folks seem to use the older stihl 088, and running at half throttle.  i'm just thinking there's a way to tune the saw so that it can function well and last as long as it can while running at half throttle.  it seems like running it as rich as possible at lowest full throttle rpm, and rich oil mix seems to be the general idea.  

but how rich can i go?  what's the downside besides frequent spark plug replacement? 

any tips, suggestions, advice would be appreciated-

[barbender]

Could you possibly describe what you are doing a little more? Any actual "milling", as I understand the term, you'd be full throttle and waiting on the saw at that. Is this something more akin to log building work, or chainsaw carving? 

[mike_belben]

I think hes freehand noodling boards.

[hamish]

Chainsaws are not meant to be run a part throttle for long periods of time.  Saws should be run at idle or full throttle.

[sawguy21]

Welcome to the scrum charles. If I understand you correctly you are running at part throttle for carving which should mean relatively short bursts. For milling, ripping logs, you should be at full throttle for maximum flow of cooling air and avoid 'lugging' which generates heat.

[charles chang]

mike is correct- i'm freehand milling- much more like carving, vs alaskan milling (which i also do, but reserve for large logs cutting slabs).  i find that with smaller logs that i want to make beams out of (6x6 and 8x), and especially if i have a stack of like 30 logs to square up, freehand milling goes sometime like 3-5x faster than alaskan mill. plus, my alaskan mill is a 48" rig.  for many situations, freehand milling saves me a ton of time and effort.  i wouldn't do this for boards though, as i'd be wasting too much wood.  i'm getting pretty decent and improving all the time, but freehand will always eat more wood than alaskan mill- for me at least.

i understand chainsaws aren't designed to be run at half-throttle, which is why i'm seeking ways to make that work longer than if i don't do any mods or leave the tuning as is.  from what i gather, there are guys in south east asia that do this freehand milling for a living, for decades.  i'm guessing they're not going through saws like crazy.  

you can say human bodies aren't designed to jump off 30 ft from buildings unto concrete floor, but parkour guys do it all the time, albeit arguably damaging their bodies in the long run.  however there are methods and techniques they practice and employ to minimize that risk.

[charles chang]

i guess i'm also trying to understand the problem of running saw at half-throttle better- what's the actual and main problem that happens when running saw at half-throttle? overheating?  what else is happening?

[charles chang]

there are lots of videos on youtube re: freehand milling, but this is the closest to how i run my saw in terms of throttle speed and rhythm- definitely not their cutting speed.  not sure what kind of wood they're cutting but my dried incense cedar (bark removed) with new ripping chains never cut that fast for me:

Cutting lumber with chainsaw. - YouTube

Crafts In - Krabi,Thailand - Lumber Milling On The Beach - YouTube

[barbender]

I don't see why you can't work the throttle, rum rum rum, so you aren't holding it at a steady half throttle. I cannot stand the sound of a saw held at a stardy 3/4 throttle, I have a guy that helps me buck firewood and he does that a lot trying to cut through the  bottom of a piece without getting into the dirt. It drives me absolutely nuts to hear a saw at those medium rpms without a load on it. They sound like they are ready to come apart.

[Ianab]

i guess i'm also trying to understand the problem of running saw at half-throttle better- what's the actual and main problem that happens when running saw at half-throttle? overheating?  what else is happening?

Problem is that chainsaw carbs are very simple mechanisms (for a carb anyway).
They are designed to operate at idle, and at full throttle. In the middle? It might produce the right mixture, or it might not.... Depends on "things". People doing chainsaw carving , which can involve a lot of part throttle for the finer work have had problems with saws running lean and overheating. .
The carb on a car or motorbike is a more complex unit, and it does a better job at keeping the mix correct over the whole rev range, because a car is expected to be able to run all day at 1/2 revs / 1/2 throttle. 

[charles chang]

barbender: do you mean why can't i work the throttle so that i'm at full throttle regularly, like every few seconds?  it's really because i'm finding freehand milling quality at its best when i can feel/sense the saw's center of gravity.  and i can best feel the saw's center of gravity while i'm NOT at full throttle, where only one or two teeth are in contact with wood at any given time, and the saw "glides".  if i run the saw at full throttle at any time, it eats through the wood way too much- committing to the cut angle on its own, versus me controlling the movement and ensuring the saw is plumb.

if i freehand mill with half to 3/4 throttle, i can get pretty impressive results (for me anyways) consistently.  i can start at one end and when i'm done at the other end, i don't need to look at the end i'm approaching.  my vertical cut is usually around 1/16" of the pencil line i drew.  so let's call that "A" quality.  if i employ full throttle (along with half throttle) at every one of my "swing" cycle (one instance of the saw movement that's repeated) i get something like a "C" quality.  i might as well as just full throttle it all the way and take what the saw gives me.  half throttling really gives me that perfect balanced saw feel, while also giving the smoothest of cuts.  most people can't really tell it was done with a chainsaw unless looking at the surface very carefully.  and it's super fast- the cutting is fast, and also there is very little setup time, especially for squaring up beams.  that's why i'm trying to make this work.

also (barbender), do you mean that you can't stand the sound of the saw at 3/4 throttle with no load from your helper because it's 4 stroking?  which brings me to the question- is it bad to repeatedly 4 stroke?

ianab: i see.  i also see why then people try to run the saw rich, and why that's not necessarily going to address the potential problem.  

so i'm left with few more questions and a strategy i might try:

1- what's the consequence of running my saw very very rich (remove my carb limiter caps), where at full throttle i'll be running a much slower rpm?  and what do you guys think would be the lowest acceptable rpm for saw like 372xp?  

2- if i run at full throttle with only a couple teeth touching, it 4-strokes.  repeating the question i asked above: what is the consequence of this (repeated 4-stroking)?

3- what's the consequence of running the saw too rich besides changing spark plugs more often?

4- i might be able to still get the feel of the saw (center of gravity) while full throttling perhaps with rakers set high- i file off my rakers every 3-4 round file touch ups, and do notice that when it's time to file my rakers i use 3/4 throttle more than 1/2 throttle.

[barbender]

The reason I can't stand when my helper runs the saw at a steady 3/4 throttle is because it doesn't 4 stroke- even though the high speed jet is set correctly, it sounds like it is probably running lean at 3/4 throttle. I think that's what others here were getting at- you can have your low speed and high speed jets set correctly, and still have lean spots at medium rpms because a saw carb doesn't have a way to correctly meter fuel there. So when my helper is running it at those rpms, my mind is screaming "get a load on that thing!" which will either bring down the rpms, or force him to use more throttle.
  I built a log home shell years back. One common technique in log home building is called "brushing", which is fanning the saw with the bar perpindicular to a horizontal surface to flatten it. It's a low load and repetitive situation where people tend to do the half throttle thing. I always blipped the throttle on/off on/off because again, a saw engine running a steady 9-10,000 rpm with a minimal load is like nails on a chalkboard to me. Even if it wasn't bad for the engine, I just can't handle the sound of it. The engines develop a high frequency resonance that just drives me nuts, and that has as much to do with the technique I use as anything. If I was you, and I needed to have the steady rpms for cut quality, I'd probably set both my low and high screws as rich as possible and still have the saw run decently.

[mike_belben]

Dirtbikes, quads etc have more elegant carburetors.   a tapered needle jet that is in a vertical guillotine slide controls mid throttle air and fuel.  The needle goes down to the main jet holder so that at part throttle the main fuel pipe is basically half plugged on a variable basis dictated by the slide.    You can change the needle for a different taper or change the clip on the needle to alter its 'timing' relative to the slide and needle jet position.. All this componentry precisely meters the part throttle air/fuel ratio with consistency.



Saws and trimmers etc have crude carbs with just a butterfly and 2 circuits.  Idle and WOT.  They dont have the means to consistently meter the part throttle air fuel ratio so it is constantly in flux between too rich and too lean as the saws vacuum demand toggles its fuel supply between the low, high and both circuit conditions.  


At idle there isnt enough vacuum to pull fuel through the main, only the pilot.  High enough rpm activates the main circuit in addition to the pilot.   But just above idle will not, despite the saw now being under load and only having the fuel supplied by the pilot.  



If it were me id get the saw started on a normal tune then fatten the pilot way out and give the saw cooldown breaks when the temp gun dictates.  Before shutting down lean the pilot back in and run it WOT under load for a bit to clean off the plug so itll start next time.  



Or id rig up a hand planer on a sawhorse sled for squaring those little ones into cants.  

[Tacotodd]

The hand planer squaring, "I" think, is the better idea.

[JohnW]

I think you mentioned time, like you have a lot of logs to mill and don't have enough time to set up your mill for each first cut.  Maybe you could find a letter rail system.  I've seen videos of some guys that look like they can get their rails set up real quick.

[charles chang]

yeah, different methods each have their benefits.  all really depends on the situation.

i don't always freehand.  but sometimes, it's the most efficient way to go about it.  other times, it's worth it (and efficient) to take the rail setup and bring alaskan mill along.  other times, might call for a planer sled (i don't use this, but i have with a router sled for flattening slabs so get the idea) and i get the benefit, if i'm looking for that smooth look and i have all logs piled up in the same spot, and only expect to take a little off- but sometimes, i'm taking off up to 6 inches from all sides- and sometimes big logs are what i'm working with, that are all over the place.  just depends.  

i understand there are other methods- just looking to see if i do decide that freehand milling is the best method for the situation, what are the things i can do to minimize risk to my saw.  

i think i got the gist of it- thanks everyone for sharing their knowledge.

just one last question though- would the new fuel injected saw from stihl basically eliminate this half throttle issue?