• Please be aware that we have recently gotten a wave of users that, when researched, are found to be from Nigeria. They are trying to sell products and asking to be paid through Zelle or Venmo leaving users with no recourse if they don't ship the product. If you suspect this activity please contact admin and we will research their information to verify their location.

ArboristSite.com Sponsors
Peak Industries


Fuel:oil ratio

GeorgiaVol

GeorgiaVol

Addicted to ArboristSite
Joined
Jan 20, 2011
Messages
1,814
Age
41
Location
Harris Co Georgia
With some saws not having an adjustment for the high jet would running a higher fuel:eek:il ratio than spec cause it to run rich? And vise-versa?
For example : older Homie calls for 32:1, how would it respond to 40:1?
 
mexicanyella

mexicanyella

ArboristSite Operative
Joined
Aug 9, 2014
Messages
116
Age
51
Location
Troy, MO
I recently inherited a new, never-started Stihl MS 170 from a relative’s estate, and it has a non-adjustable carb. It ran too rich on 50:1, four-stroking at any throttle setting or load. I tried 32:1, which I run in my other saws (couple of Poulans), and it made enough difference that in the cut, it’s loaded enough to smooth out and pull well.

I notice a bit more smoke on cold starts but warmed up and under a load I don’t see smoke. Time will tell whether it requires more frequent spark arrestor or exhaust port cleaning...my Poulans and a 28-year-old Stihl FS72 trimmer have lasted well on that fuel mix for years with no carbon accumulation issues...for real.
 
OM617YOTA

OM617YOTA

ArboristSite Operative
Joined
Jan 20, 2020
Messages
166
Location
Oregon
Welp, now you gone and done it. Just what we needed, an oil thread.

I've read that the more oil in a given volume of mix, the less fuel there is in that volume of mix, and therefor a richer oil mix will lead to a leaner air/fuel ratio. This hasn't been my experience. I normally run 40:1 premix, and somehow wound up with one can of 50:1 premix. Running that 50:1 premix in my 034S required richening the high end to get it to four stroke out of the cut again. Clearly in this situation the oil was burning as well and contributing to the air/fuel ratio, and less oil meant a leaner air/fuel ratio.

Before the premix, I of course mixed my own fuel and tuned for whatever mix I was running and the conditions I was running in.

My take away is that until I own an autotune or M-tronic or eventually an EFI saw, I won't own a fixed jet saw. I need to be able to adjust the screws myself for the conditions at hand, whatever they may be.
 
mexicanyella

mexicanyella

ArboristSite Operative
Joined
Aug 9, 2014
Messages
116
Age
51
Location
Troy, MO
One other fuel-related thing I noticed with that new MS170...it came with an unopened gallon of Stihl 50:1 fuel (motomix? Something like that). On that fuel, it ran like crap. Blubbering like the choke was left on. Nearly unusable!

My new Redmax trimmer/pole saw is a strato two-stroke and loved that motomix; ran great and smelled like race gas exhaust. Oddly, the Redmax runs equally well on 32:1, but with noticeable two-stroke exhaust smell. No visible smoke, though.

As soon as the MS170 starts acting up it will receive an adjustable carb. I do like that little saw so far, stupid carb notwithstanding.
 
Old2stroke

Old2stroke

Never too many toys
Joined
Jan 24, 2016
Messages
580
Age
78
Location
Ottawa, Canada
I run a little Homie XL with no high speed screw. Runs great on 40:1, but just a little rich. Would 32:1 lean it out then?
Yes, it should lean it out a bit. I've had a number of older saws with fixed main jets, some were specified to run on 16:1 and if I tried to run them on my usual 30:1 mix, they would run way too rich.
 
GeorgiaVol

GeorgiaVol

Addicted to ArboristSite
Joined
Jan 20, 2011
Messages
1,814
Age
41
Location
Harris Co Georgia
I'm starting to understand this a little more now. So with the better oils made today, less is needed to provide lubrication, but the equipment HAS to be set leaner. If you run a richer oil mix, then the equipment has to be set a little fatter. Correct? I've always just run 50:1 in my string trimmers and 40:1 in my saws, but the fixed jet saws never ran quite right.
 
SteveSr

SteveSr

Addicted to ArboristSite
Joined
Mar 3, 2003
Messages
1,539
Location
Raleigh, NC
Website
Visit site
I recently inherited a new, never-started Stihl MS 170 from a relative’s estate, and it has a non-adjustable carb. It ran too rich on 50:1, four-stroking at any throttle setting or load. I tried 32:1, which I run in my other saws (couple of Poulans), and it made enough difference that in the cut, it’s loaded enough to smooth out and pull well.
That must be an oddball 170. In my experience these are almost all borderline too lean but then I am only 250' above sea level. Can you post a photo of the silver engine family label on the handle so that we can know when it was manufactured? Also what elevation and temperatures are you cutting at? Both of these will affect the tuning.
 
mexicanyella

mexicanyella

ArboristSite Operative
Joined
Aug 9, 2014
Messages
116
Age
51
Location
Troy, MO
I am in east central Missouri, around 700’ elevation, and I’ve used the saw in temps ranging from 30F to about 90F so far. I will look for the label and post a photo of it shortly.
 
mexicanyella

mexicanyella

ArboristSite Operative
Joined
Aug 9, 2014
Messages
116
Age
51
Location
Troy, MO
02908C42-2BD8-4E73-87AD-B1E8F24FA0D2.jpeg
That must be an oddball 170. In my experience these are almost all borderline too lean but then I am only 250' above sea level. Can you post a photo of the silver engine family label on the handle so that we can know when it was manufactured? Also what elevation and temperatures are you cutting at? Both of these will affect the tuning.
Sorry for the delay! From these two photos I think it’s clear that if you want a rich-running MS170, you need to find one from 2012 or 1948.

Man, that’s a long production run. Those Germans! 8D032215-B8CF-4362-884A-817FA0E578D0.jpeg
 
mexicanyella

mexicanyella

ArboristSite Operative
Joined
Aug 9, 2014
Messages
116
Age
51
Location
Troy, MO
As an aside, how about my uncle, buying a 2012 MS170 and sticking it on the shelf, never fueled or run, for seven years? Lucky break for me, but if I’d bought that thing I’d have been rarin’ to go, looking for stuff to go cut with it. Calling neighbors: “Hey, you want to see my new chainsaw? Got any trees that need to come down, or be trimmed? I’ll give you fifty bucks...”
 
SteveSr

SteveSr

Addicted to ArboristSite
Joined
Mar 3, 2003
Messages
1,539
Location
Raleigh, NC
Website
Visit site
View attachment 827073
Sorry for the delay! From these two photos I think it’s clear that if you want a rich-running MS170, you need to find one from 2012 or 1948.

Man, that’s a long production run. Those Germans! View attachment 827072
Sorry, those aren't the label that I was looking for. There should be another one located under the throttle trigger that has "Engine Family" on it. On that lable you'll find a MD or DOM code which can be decoded into a manufacturing date. The 2012 date is on the UL safety sticker. All we know is the saw is later than 2012. But it does blow my theory that this is a very old version of the saw before EPA began tightening the screws.

BTW, how dirty is the air filter? Remove it to look at the bottom side. The top side is the filtered side and it will always look clean.
 
Broken

Broken

The Great White North...Eh !
Joined
Mar 28, 2010
Messages
717
Age
69
Location
Canada
With some saws not having an adjustment for the high jet would running a higher fuel:eek:il ratio than spec cause it to run rich? And vise-versa?
For example : older Homie calls for 32:1, how would it respond to 40:1?
I run all my saws @ 50:1 Sabre . That includes 50+ yr old Pioneers . Exception is for initial break in of a new saw. , which involves 2 tanks at 40:1 . P.S. don't confuse fuel to air ratio with fuel to oil ratio , to separate considerations although one may and can effect the other , especially @ extreme elevations or temperature ranges !
 
GeorgiaVol

GeorgiaVol

Addicted to ArboristSite
Joined
Jan 20, 2011
Messages
1,814
Age
41
Location
Harris Co Georgia
I run all my saws @ 50:1 Sabre . That includes 50+ yr old Pioneers . Exception is for initial break in of a new saw. , which involves 2 tanks at 40:1 . P.S. don't confuse air to fuel ratio with fuel to oil ratio , to separate considerations although one may and can effect the other , especially @ extreme elevations or temperature ranges !
I tune all my saws to run on 40:1 with the exception of these that have fixed jets. I will be getting a Shindaiwa 300s running soon and it also has a fixed jet. Just making sure I have an idea what to expect from it. It needs 50:1 per manufacturer spec.
 
Broken

Broken

The Great White North...Eh !
Joined
Mar 28, 2010
Messages
717
Age
69
Location
Canada
I tune all my saws to run on 40:1 with the exception of these that have fixed jets. I will be getting a Shindaiwa 300s running soon and it also has a fixed jet. Just making sure I have an idea what to expect from it. It needs 50:1 per manufacturer spec.
Just do a plug check after one or to cuts of hardwood . 40:1 should be fine. In the fixed jet saws a little more oil is warranted .
 
mexicanyella

mexicanyella

ArboristSite Operative
Joined
Aug 9, 2014
Messages
116
Age
51
Location
Troy, MO
Sorry, those aren't the label that I was looking for. There should be another one located under the throttle trigger that has "Engine Family" on it. On that lable you'll find a MD or DOM code which can be decoded into a manufacturing date. The 2012 date is on the UL safety sticker. All we know is the saw is later than 2012. But it does blow my theory that this is a very old version of the saw before EPA began tightening the screws.

BTW, how dirty is the air filter? Remove it to look at the bottom side. The top side is the filtered side and it will always look clean.
The rich running occurred from the very beginning; when I received the saw last fall the tank had never been filled and the exhaust louvers had zero deposits.

I will look for the other label when I get back home later today. I don’t suppose the long number etched into the chassis below the muffler, visible in the one photo, can be decoded for any date info...?
 
SteveSr

SteveSr

Addicted to ArboristSite
Joined
Mar 3, 2003
Messages
1,539
Location
Raleigh, NC
Website
Visit site
Just do a plug check after one or to cuts of hardwood .
IMHO plug checks aren't real useful as these engines aren't typically run hard enough and long enough to show any issues. By that time it is the saw has seized.

For example I ran an MS260 16" bar buried in fresh oak and it was definitely getting "warm" according to the "tink, tink" sound it made while it cooled off after shutdown. I checked the plug when I got home and it was light brown indicating no problem. Yes, it was shut off after the last buried bar cut so didn't get loaded up at idle. The plug showed no issues but it was still getting hotter that I probably should have let it.

In the fixed jet saws a little more oil is warranted .
This is just plain wrong and dangerous! more oil = less gas which makes an already lean mixture even leaner. A good way to burn up a saw! There are multiple threads on this board about this.
 
mexicanyella

mexicanyella

ArboristSite Operative
Joined
Aug 9, 2014
Messages
116
Age
51
Location
Troy, MO
IMHO plug checks aren't real useful as these engines aren't typically run hard enough and long enough to show any issues. By that time it is the saw has seized.

For example I ran an MS260 16" bar buried in fresh oak and it was definitely getting "warm" according to the "tink, tink" sound it made while it cooled off after shutdown. I checked the plug when I got home and it was light brown indicating no problem. Yes, it was shut off after the last buried bar cut so didn't get loaded up at idle. The plug showed no issues but it was still getting hotter that I probably should have let it.


This is just plain wrong and dangerous! more oil = less gas which makes an already lean mixture even leaner. A good way to burn up a saw! There are multiple threads on this board about this.
I don’t say this to be argumentative at all...but I have run into a couple of small two-strokes with fixed high-speed jets which seemed to run too rich on the top end. One was an old Homelite ST-200 trimmer (engine at the top, big fat curved shaft, single-line auto-feed head...and I think the same engine as one of the little red plastic saws. XL-2, maybe?) That was at my Midwest 725’ elevation in the summer. 32:1 helped a little, and a couple of additional holes drilled in the exhaust outlet finished the job. Ran great and cut really well for a couple summers...although my hearing range may now top out at about 12 kHz instead of 20kHz! LOUD trimmer.

The other is an old 18cc Weedeater Featherlite (square housing, not the newer jellybean-shaped housing) my Stepmom uses around her garden. She lives west of Denver CO at about 8,500-9,000 feet, and runs 50:1 in that and her saws (MS170, Husqvarna 50). When I visit I get weedeater detail. I mixed up a few quarts of fuel at different ratios last time as an experiment. It seemed to work about right on 20:1, a holdover from my dirt bike days as a kid. Smoked a
bit on that fuel, but ran pretty well considering the altitude.

I wonder how her MS170 does on 50:1 up there. I would ask but I don’t think she speaks rich/lean.
 
Broken

Broken

The Great White North...Eh !
Joined
Mar 28, 2010
Messages
717
Age
69
Location
Canada
IMHO plug checks aren't real useful as these engines aren't typically run hard enough and long enough to show any issues. By that time it is the saw has seized.

For example I ran an MS260 16" bar buried in fresh oak and it was definitely getting "warm" according to the "tink, tink" sound it made while it cooled off after shutdown. I checked the plug when I got home and it was light brown indicating no problem. Yes, it was shut off after the last buried bar cut so didn't get loaded up at idle. The plug showed no issues but it was still getting hotter that I probably should have let it.


This is just plain wrong and dangerous! more oil = less gas which makes an already lean mixture even leaner. A good way to burn up a saw! There are multiple threads on this board about this.
As for plug checks light brown or tan is showing a semi lean condition .The only lighter shade of grey or white have been straight gassed saws lol. Brown to dark brown is optimal . A little more oil as I advised was within my choice of 50:1 in a adjustable jetted carb vs 40:1 in a fixed jet carb , thats all I was saying since enriching the overall fuel to air ratio in the fixed jet carb is sketchy at best . Are you saying 40:1 is ill advised ? P.S. persoǹally I do not favour any non adjustable carb or the new autotune / electronic controlled version . Fully adjustable jets and a tach for proper tuning validated by a proper plug check !
 
Top