H 3120xp Slabbing-milling Oil mix ratio

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Drew Young

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Hi folks

I have been a lurker here for a couple of years and specifically reading the various threads on oil ratio. I have read a wide range of thoughts and opinions on 50: 1 versus 40: 1 and a few others. Admittedly there have been some very interesting and convincing opinions.

However, I also sense that not all factors are always considered. For example, newness of the machine, regular vs synthetic oil, the activity (cutting vs milling), the engine CCs, chain type, wood species, width...maybe even altitude!

So, heres my situation:

Im running a big machine, H 3120, which I have hooked up to a homemade saw mill rig.

  • I'm running a 4' bar.
  • Ripping chain
  • And while I do take the saw out to cut I'm primarily using it for milling
  • Using synthetic 2 stoke
  • My machine is used but has been refurbished and certified.
  • Mostly cut hardwoods


----

At any rate, based on my list above what do you all recommend for my oil ratio?


(Ps I'll snap some pictures of my new milling rig tommorow)

Thanks folks
Drew
 
32:1, if not more oil. 32:1 is still tolerable to breath while milling and seems to provide a decent margin of error in terms of oil residue on the bearings.

Piston and cylinder do not need as much, the bearings do. If possible flip that saw up so it sits normal while idling between cuts. Listen to the idle between cuts make sure it settles into a consistent idle and is not sounding different after long cuts. Set the carb as rich as possible while idling. It is tricky with the 3120, due to the carb.
 
Gut the baffle out of the muffler, leave the stock outlet, just gut the baffle out.. it's a pos restricted design that traps heat, you want to let out the extra heat generated when milling. There's No H screw on carb but you can Richen up the L for the extra fuel at idle, it helps, let it idle as much as possible, keep it under load not over reving in the cut, keep the chain sharp and depth gauges set a tad lower so it's not just sitting there doing fuk all overreving in the cut ... 32:1, use a good 2stroke bike filter oil to oil your air filter too
 
Gut the baffle out of the muffler, leave the stock outlet, just gut the baffle out.. it's a pos restricted design that traps heat, you want to let out the extra heat generated when milling. There's No H screw on carb but you can Richen up the L for the extra fuel at idle, it helps, let it idle as much as possible, keep it under load not over reving in the cut, keep the chain sharp and depth gauges set a tad lower so it's not just sitting there doing fuk all overreving in the cut ... 32:1, use a good 2stroke bike filter oil to oil your air filter too


If he has the stock carb with the fixed jet this may not be a good idea.

My 395xp muffler was quite free flowing, I used a screw driver to open up the little port and bend the little teeth on the outlet back. This proved to be more than enough for my needs. Saw doesn’t get that hot so I know the muffler is flowing enough.
 
Gut the baffle out of the muffler, leave the stock outlet, just gut the baffle out.. it's a pos restricted design that traps heat, you want to let out the extra heat generated when milling. There's No H screw on carb but you can Richen up the L for the extra fuel at idle, it helps, let it idle as much as possible, keep it under load not over reving in the cut, keep the chain sharp and depth gauges set a tad lower so it's not just sitting there doing fuk all overreving in the cut ... 32:1, use a good 2stroke bike filter oil to oil your air filter too

What is a baffle?

I apologize I'm not an engine expert.
 
32:1, if not more oil. 32:1 is still tolerable to breath while milling and seems to provide a decent margin of error in terms of oil residue on the bearings.

Piston and cylinder do not need as much, the bearings do. If possible flip that saw up so it sits normal while idling between cuts. Listen to the idle between cuts make sure it settles into a consistent idle and is not sounding different after long cuts. Set the carb as rich as possible while idling. It is tricky with the 3120, due to the carb.


What do you mean set the carb as rich as possible? Fully open ?
 
If he has the stock carb with the fixed jet this may not be a good idea.

My 395xp muffler was quite free flowing, I used a screw driver to open up the little port and bend the little teeth on the outlet back. This proved to be more than enough for my needs. Saw doesn’t get that hot so I know the muffler is flowing enough.
This is what I was thinking too. I'd run as much oil as you can without leaning out the air:fuel ratio. More oil on a fixed jet carb = lean saw. But if carb has been modified & has aan adjustable H-screw, forget what I've written & run what you wish.
 
Something else I was thinking.... The original owner lived in Alaska and I live near Washington DC so I think there could be some climate difference.

What am I looking for in terms of adjusting ... Is this about altitude or humidity?
 
If he has the stock carb with the fixed jet this may not be a good idea.

My 395xp muffler was quite free flowing, I used a screw driver to open up the little port and bend the little teeth on the outlet back. This proved to be more than enough for my needs. Saw doesn’t get that hot so I know the muffler is flowing enough.

The 3120 is badly restricted by a internal baffle more so than a 395, (395 can also be tuned having a adjustable H screw ). By removing only the internal baffle it will not open the exhuast outlet any bigger, so no effect on changing muffler outlet size. I did it to mine it was nice and cool running afterwards.

I also drilled the set H jet a size up because I opened up the muffler "outlet" as well.
 
What is a baffle?

I apologize I'm not an engine expert.
It's a small diameter section of steel tube that's inside the muffler that gasses have to travel threw before dumping out the muffler outlet, it quietens them but traps heat from dissipating, not so much a issue in cross-cutting as was intended with saws .. saws where not designed for the sustained long hard cutting milling requires, lots of saws die in a milling situation if not modified to help them out .. A cold climate and softwoods may help in northern hemisphere but much harder on saws in Australia in our conditions.

Less heat trap in the saw = win in my book!
 
Keep recoil and cylinder fins clear from chips and stuff, remove baffle and muffler mod. Richen mix, 32:1 or 25:1 ratio.

Milling/slabbing are hard work, they get very hot and start to cook oil away. Thats why saws get burnt using 50:1, let it idle like said above for a minute or more to let oil accumulate on bottom end and to feed internal components with more oil
 
What do you mean set the carb as rich as possible? Fully open ?

The carb on the 3120 can be adjusted on the low side or idling mixture and the idle position of the throttle plate. The low side screw determines how much fuel can be sucked into the venturi with the throttle plate in the idle position. If possible it would be handy to turn that screw counterclockwise as much as possible before the idle becomes so unstable that it floods into a stall. This is going to be a very small amount of a turn, think an 1/8 of one full rotation at most.

However, before you do anything at all to the saw you should get some time using it as it is. Mount up a bar and chain and run some tanks of fuel through it cutting some wood. Also be a good idea to watch some YouTube videos about 3120s and how to set carbs on chainsaws. Might want to watch some videos about chainsaw milling and chain sharpening as well.

A well maintained sharp chain being used properly will keep your 3120 running. The chain is the most important part, then the air filter. The best oil at 32:1 will not save a muffler modified saw with a poorly sharpened chain being pushed through the wood while sucking fine saw dust through the poorly maintained air filter.
 
That's why we recommend a good filter oil, like motul 2stroke dirtbike air filter spray oil ....it's very important for the big bores, they suck some serious air. You Can also use a woman's pantyhose(the thin woven silky smooth kind) as a extra layer of filter over the main oiled filter. Keep a sharp chain is key and depth gauges in check reduces fines into the intake air filter area.
 
I feel like such an amateur....I am, really. Ive used the saw for about 10 hours and had great success milling wide oak.

Biggest issue now is that I cant get it started...Ive cleaned the spark plug.... dumped the gas/oil....new gas.....not sure whats going on.
 
That's why we recommend a good filter oil, like motul 2stroke dirtbike air filter spray oil ....it's very important for the big bores, they suck some serious air. You Can also use a woman's pantyhose(the thin woven silky smooth kind) as a extra layer of filter over the main oiled filter. Keep a sharp chain is key and depth gauges in check reduces fines into the intake air filter area.

where do I spray this stuff?

And forgive me...I still don't quite understand what the baffle is...Ive been searching google images. Pics would really help me. Im an advanced metal craftsman so I can do the mods...just don't know exactly what I should be modifying.

Big thanks
 
If it is no longer starting after starting easily than something is amiss.

If it will start with a little bit of mixed fuel poured manually into the carb and run until that fuel is burned it is time to checked the fuel system. Around a teaspoon at most, not trying to get a confession out of it. Throttle wide open, choke off.

If it does not start with a manual prime, check for spark while pulling the saw over. Inline spark checker is the easiest way, available at auto part store and places like harbor freight. I have used a harbor freight one for years.

If it has spark, will not start with a manual fuel prime then it is time to check the piston and cylinder. Pulling the muffler is a decent way to get a look for a toasted P/C.
 
It's a small diameter section of steel tube that's inside the muffler that gasses have to travel threw before dumping out the muffler outlet, it quietens them but traps heat from dissipating, not so much a issue in cross-cutting as was intended with saws .. saws where not designed for the sustained long hard cutting milling requires, lots of saws die in a milling situation if not modified to help them out .. A cold climate and softwoods may help in northern hemisphere but much harder on saws in Australia in our conditions.

Less heat trap in the saw = win in my book!

To fix these problems, stihl and echo thinked out of the box and designed saws that are probably the most suited for milling 070/090 and cs1200/1201.

All aluminium muffler with fins, which 95% of most make and models dont have. The muffler itself is a heatsink, wide open mufflee exit. Both has louvres style exit, cylinder fins on the side where cooling air exit are wide open and unrestricted, cases are thick and big which sheds alot heat too. Both saws come with manual oiler and has low down torque. These are ultimate milling saw characters
 
I would run at a minimum 32:1 and woukdnt at all be scared to run 20:1. milling is very hard on a saw engine. Especially with a 48" bar.
I'm not familure with the carb setup on a 3120, but is it possible to drill out the fixed jet or replace it with the next size bigger? Some Stihl fixes jet carbs have replicable fixed jets.
Also Inwould run a quality semi synthetic or synthetic bike oil.
 
The 3120 can be a coil limited saw, I think the earlier versions were around 10500 rpm limits.

If it was purchased used then it may have had a different coil installed and or have had the carb modified. A couple of different site sponsors have provided that carb service over the years. If in the future milling with a stock 3120 becomes a favorite thing, having the carb modified and coil replaced are the first mechanical modifications to the saw I would recommend. Not at all required to successfully mill lots of lumber however they can make it a better experience and remove some of the guess work from running the saw.

The old school Stihl and Echo large saws are neat however not typically an option at a reasonable price point to the average shopper in the US, which is sad. Who would not want an Echo 1200/1?
 
Hi folks

I have been a lurker here for a couple of years and specifically reading the various threads on oil ratio. I have read a wide range of thoughts and opinions on 50: 1 versus 40: 1 and a few others. Admittedly there have been some very interesting and convincing opinions.

However, I also sense that not all factors are always considered. For example, newness of the machine, regular vs synthetic oil, the activity (cutting vs milling), the engine CCs, chain type, wood species, width...maybe even altitude!

So, heres my situation:

Im running a big machine, H 3120, which I have hooked up to a homemade saw mill rig.

  • I'm running a 4' bar.
  • Ripping chain
  • And while I do take the saw out to cut I'm primarily using it for milling
  • Using synthetic 2 stoke
  • My machine is used but has been refurbished and certified.
  • Mostly cut hardwoods


----

At any rate, based on my list above what do you all recommend for my oil ratio?


(Ps I'll snap some pictures of my new milling rig tommorow)

Thanks folks
Drew
Out of curiosity how long a full of gas last cutting big trees?
Thanks
 
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