Fuel:oil ratio

[North by Northwest]

I think I am a bigger two-stroke nerd than you are.

Now that's pretty funny !

 

[GeorgiaVol]

If you feel confident in your ability to identify lean running symptoms, that should work.

One thing to keep in mind is, chainsaws are either idling or WOT. So the margin for detecting a too-lean condition is narrower than it would be on a trimmer (idling or low-load part-throttle most of the time). Trying the different mix ratios in my stepmom’s trimmer was pretty low-risk; it’s not a very highly-stressed engine, it’s at high altitude on top of that, and it’s a Featherlite facrissake. Blew up a featherlite? No big whoop. Go find three more in your neighbor’s dumpster.

Aside from idle mixture settings, Most of your “this thing is too lean” cues are easiest to detect as flat spots in your response and acceleration, or slow return to idle...and a saw will give you less opportunity to observe and react to those cues since it spends very little time doing throttle transitions from one carb circuit to another. So you have to pay pretty close attention to that idle-to-WOT transition, how promptly it comes back to idle, any hint of flat spots in the acceleration response, exhaust smell...thus the “tune it to blubber a little out of the cut and pull clean in the cut” thinking. Gives you a margin of error, since a saw is less likely to survive running on the razor edge of tip-top mixture accuracy.

I read a pretty cool book about GP road race bikes in the early 60s, when two-strokes were starting to eat four strokes alive. Those guys were riding three-figure speeds into corners on the Isle of Man, next to stone walls and big trees, trying to hear signs of impending seizure so they could hopefully pull the clutch in fast enough to not be turned into impact sausage. A lot of them were not quick enough, apparently.

yes, that is what I listen for, that "4 stroke" sound outside of the cut. I know what it sounds like when a saw screams from being too lean. I burned one up. Early learning, that's what got me into saws. Typically I tune on the side of caution and just leave it fat a little.

 

[mexicanyella]

My Poulan Pro 5020AV's piston could tell you a story or two about me trying to tune my first strato engine that way. Apparently strato engines are a little different and less tolerant of error. After 15 years of running a little Poulan 2150 a lot and thinking I was pretty slick with the tuning, I got through the too-rich break-in period on that 5020, leaned it out so it would get out of its own way and seized it. Still runs and cuts but I am more conservative now, and at some point will be tearing it down. Kind of embarrassing.

 

[Deleted member 117362]

yes in theory ! Try it out and get back to us !

Is that like when people add oil into their snowmobile that is oil injected when it's cold out, thinking added oil will lubricate engine. Oops, sciezed motor.

 

[mexicanyella]

Seizing a snowmobile or an outboard is probably a pretty big bummer, compared to a saw or a bike. Expensive and harder to get home.

Hey, let's go seize an ultralight, or a gyrocopter! What's the worst that could happen?

My dad knows a guy who made a "fuel mixing error" in an ultralight back in the 80s. Seized it, crashed and broke his leg pretty badly.

 

[North by Northwest]

Is that like when people add oil into their snowmobile that is oil injected when it's cold out, thinking added oil will lubricate engine. Oops, sciezed motor.

Actually , much more incidents of snowmobiles cold seizing due to operator error than adding a few xtra ounces of premix . Especially these new liquid cooled mountain sleds . Some of these cowboys jump on their sleds without sufficient warm-up and hit the deep powder , bam locked solid lol. I run 3 ounces of Premium Synthetic as premix in 10 gal cdn.fuel tank for insurance in my oil injected 700 Polaris SKS . Also run 1 heat range cooler NGK plugs , 5000 miles on the big Liberty twin !

 

[North by Northwest]

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.

if your using Group III oil or above potential for carbon fouling will be significantly reduced . I try and to run FC & FD Group oil in my air-cooled engines . Back in the 70,s when I raced snowmobiles semi professionally the premix dino mineral oils required weekly engine teardown to decarbonize heads & rings , especially the Klotz castors , nature of the beast !

 

[North by Northwest]

yes, that is what I listen for, that "4 stroke" sound outside of the cut. I know what it sounds like when a saw screams from being too lean. I burned one up. Early learning, that's what got me into saws. Typically I tune on the side of caution and just leave it fat a little.

My Dolkita 5105H requires a tach impossible to determine when it's blubbering or hitting the chip @ 13,800. Much easier with the 576 xp since I ordered it without the Autotune

 

[Bruiser1]

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.

You do realize the lower you go in ratio the oil is thicker if you have a 50 to 1 it’s leaner. Higher more gas less oil ,lower More oil less gas. As for me I always like leaving mine little in the “rough”Little bit more oil As opposed to gas when I’m adjusting the carburetor

 

[mexicanyella]

What I have read (mostly in MX magazines concerning two-stroke dirt bikes), which has matched my actual experience with trimmers, a couple of saws and the maddening-to-jet-right YZ490 I had for awhile, is that more oil on the premix means less fuel, but the same amount of air, thus a leaner fuel/air mixture getting to the engine. So you jet it richer to compensate. Back in those magazine-reading, dirt-biking days you were “supposed” to run 20:1 in a lot of new MX bikes, but since real racers (I was not!!!) would do frequent top end overhauls, they would run 32:1, 40:1 or 50:1, claiming sharper throttle response once they rejetted (leaner; smaller main jet and/or jet needle on a higher clip groove) to compensate.

I ended up running 32:1 in everything; in the bike it fouled less plugs than 20:1 and it seemed to work well in the saws and trimmers. So I have stuck with that despite the fact that lots of people seem to have good results from 50:1.

Like the experience I had with the MS170 blubbering even in the cut on 50:1, the YZ was a blubbering, sputtering pig on 50:1 (what the prior owner ran in it: “Always use Bel-Ray MC-1+!!!” He said) but ran pretty well on 32:1. Eventually I did make some carb changes but not so I could change fuel ratios. I was just trying to smooth it out in the midrange. It pulled well at WOT, not that my cupcake play-riding ass spent much time up there.

 

[North by Northwest]

What I have read (mostly in MX magazines concerning two-stroke dirt bikes), which has matched my actual experience with trimmers, a couple of saws and the maddening-to-jet-right YZ490 I had for awhile, is that more oil on the premix means less fuel, but the same amount of air, thus a leaner fuel/air mixture getting to the engine. So you jet it richer to compensate. Back in those magazine-reading, dirt-biking days you were “supposed” to run 20:1 in a lot of new MX bikes, but since real racers (I was not!!!) would do frequent top end overhauls, they would run 32:1, 40:1 or 50:1, claiming sharper throttle response once they rejetted (leaner; smaller main jet and/or jet needle on a higher clip groove) to compensate.

I ended up running 32:1 in everything; in the bike it fouled less plugs than 20:1 and it seemed to work well in the saws and trimmers. So I have stuck with that despite the fact that lots of people seem to have good results from 50:1.

Like the experience I had with the MS170 blubbering even in the cut on 50:1, the YZ was a blubbering, sputtering pig on 50:1 (what the prior owner ran in it: “Always use Bel-Ray MC-1+!!!” He said) but ran pretty well on 32:1. Eventually I did make some carb changes but not so I could change fuel ratios. I was just trying to smooth it out in the midrange. It pulled well at WOT, not that my cupcake play-riding ass spent much time up there.

Yeah that pretty well sums it up . Use what works within the majority of your applications . Fine tune from there . As I tied to explain plug checks are the only proven security that the oil you are using is doing its job . Altitude which effects barometric pressure and engine tuning within air to fuel radio's will vary . Oil to fuel radio's are set accordingly . I have raced in the dirt on the snow and ice , chainsaw r&r is not rocket science rather common sense ! The majority of current small engine complaints are either directly related if not contributed to ethanol fuel that is **** !

 

[GeorgiaVol]

Yeah that pretty well sums it up air to fuel ratios cakes . . Use what works within the majority of your applications . Fine tune from there . As I tied to explain plug checks are the only proven security that the oil you are using is doing its job . Altitude which effects barometric pressure and engine tuning within air to fuel radio's will vary . Oil to fuel radio's are set accordingly .

I see a lot of trying fuel/oil ratios in the future to get my fixed jet saw to run right. Lol

 

[rogue60]

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 !

I run my ms170 on 32:1 sometimes 25:1 from new it was still fat more oil did not lean it out.
Modding it to let more air in (airbox) and opening up the muffler a little at a time cleaned it up runs sweet after doing that still has stock carb no high or low.

 

[mexicanyella]

I run my ms170 on 32:1 sometimes 25:1 from new it was still fat more oil did not lean it out.
Modding it to let more air in (airbox) and opening up the muffler a little at a time cleaned it up runs sweet after doing that still has stock carb no high or low.

I think a muffler mod is in my MS170’s future also. I think it’s still slightly on the fat side of optimum.

Admittedly, this kind of thinking resulted in a lightly seized 5020AV a week or two ago. Dammit.

Those non-adjustable MS170 carbs must have some pretty wide manufacturing tolerances if most people find them too lean. Definitely not the case with mine.

 

[Old2stroke]

Non adjustable carbs on a chainsaw are a real pain but what's worse are the fixed jet carbs found on lawnmowers and snowblowers. Blow them out with cleaner and compressed air and if they still don't work you are in for a lot of fun trying to find out what's plugged.

 

[North by Northwest]

I see a lot of trying fuel/oil ratios in the future to get my fixed jet saw to run right. Lol

Some people remove limitors or welch plugs to get at the jets to properly tune . The epa carbs on some saws cannot be tuned adequately . The majority of my newer saws have muffler mods to increase performance help the saw run cooler . The worst offenders were stihl in 2005 - 2010 era also echo they came very lean tuned from the factory . To the extent that resetting was required in some geographical locations .

 

[GeorgiaVol]

Some people remove limitors or welch plugs to get at the jets to properly tune . The epa carbs on some saws cannot be tuned adequately . The majority of my newer saws have muffler mods to increase performance help the saw run cooler .

I have never removed welch plugs in a carb. What do they do?

 

[North by Northwest]

I have never removed welch plugs in a carb. What do they do?

Prior to the new jet adjusters heads , e.g. pacman , spline & double d heads the factory installed aluminium caps or plugs over the adjusters to prevent tampering . Some manufacturers actually epoxied over the screws lol. Just a form of epa regulatory compliance to enable sales world wide .

 

[GeorgiaVol]

Ever seen a Shindaiwa carb? Weird looking. Similar to an Echo string trimmer carb, but on a chainsaw.

 

[North by Northwest]

Ever seen a Shindaiwa carb? Weird looking. Similar to an Echo string trimmer carb, but on a chainsaw.

Yes on majority of small engine carbs across the board . I have seen welch plugs on snowblowers , grass trimmers , chainsaws . Echo or Shindaiwa did also in the past . Majority of manufacturers have gone the route of speciality adjuster head configuration or a fixed jet configuration .