Yea...lol. Those same engineers put a fixed high side jet on the Ms260 and then plugged the muffler up. Result was many scored skirts and chitty running saws.
mixing ratios for 2 stroke chainsaws
- Thread starter sawmill sam
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Air cooled motors do not have tight tolerances.
Pretty much.
Thanks for admitting that. And I guarantee what I said was 100% accurate.
I've messed around with cr500 motors that where in various states of tune for many years. I would not run any less than 40:1 in that particular motor. I always ran mine at 32:1 or more depending on load/use. The cast iron cylinder liner in concert with the forged pistons I prefer for that application are not very forgiving.
Oh , i had a lot of intense moments understanding the design rational of fixed main jets on numerous recreational engines . That were to be utilized within various elevations throughout the world . No achievable tuniability without a complete jet replacement . Then lets make it even worse & restrict the exhaust capabilities or install limitors or welch plugs or even epoxy to deter operator capable engine tuning for basic temperature or barometric pressure swings . Oh don't touch that , it will void your warranty , seriously as if I give a **** about any expressed limited warranty lol. I did the same with my 1980 lowrider back in the day . Drilled out the Welch plugs adjusted the low speed jet & replaced the high speed jet . Hell , it was running so rich at 6000' through the Smokie Mountains , it would barely start & run , until I gapped the plugs @ .050 to get to the closest dealer to borrow a drill & installed the new jet & retuned the bike . Anyhow yeah Engineer's .
Thank God they then trashed the fixed jet Mikuni's & went back to tunable Kehien CV 's the next yr ! 
I hear you , I never personally ran any MX bike that lean , especially at around sea level here , not near enough safety factor . I always ran 40:1 in my Enduro's & 32:1 in a Moto-x when modern quality 2T oil became the norm . I always like a little fatter oil ratio in performance related equipment . Especially , within Quality Forged pistons & Likosil performance liners . Oils cheaper than aftermarket parts & unscheduled downtime !
My first 260 would barely run with the stock carb. Very lean!Oh , i had a lot of intense moments understanding the design rational of fix high speed jets on numerous recreational engines . That were to be utilized within various elevations throughout the world . No achievable tuniability without complete jet replacement . Then lets make it even worse & restrict the exhaust capabilities or install limitors or welch plugs or even epoxy to deter operator capable engine tuning for basic temperature or barometric pressure swings . Oh don't touch that it will void your warranty , seriously as if I give a **** about any expressed limited warranty lol. I did the same with my 1980 lowrider back in the day . Drilled out the Welch plugs adjusted the low speed jet & replaced the high speed jet . Hell , it was running so rich at 6000' through the Smokie Mountains it would barley run until I gapped the plugs @ .050 to get to the closest dealer to borrow a drill & installed the new jet & retuned the bike . Anyhow yeah Engineer's .
What was you elevation then , about sea level more or less ?
As business decision your most likely correct !
This one I just picked up has the carb with both screws, has plastic limiters I need to remove. I am going to drill 2 more holes in the muffler and see how I like it.
Liquid cooled engines do have much tighter tolerences . Not much has changed within air cooled tolerances , perhaps better quality components due to more precise metallurgy !
UP of MI so maybe 1200'.
Will some oils actually dry up over time? I just pulled apart a junkyard Husqvarna 50 that had a very nice oem piston/cylinder in it. The crankshaft was very difficult to move and I thought the bearings were shot. On a hunch I oiled them up and now they move freely. Oiling the seals seemed to make no difference.
This is a cause for concern if I was going to store a saw for any length of time, I'm now thinking fogging will be mandatory.
It seems so little oil was left in the crank of that saw, yet there is no scoring and it would be fine with just a new ring. Or perhaps this is carbon from blow by that has hardened over time and the oil loosened it up? It did have some carbon stains in the crankcase.
Maybe that extra bit of oil at 40:1 vs 50:1 will have another benefit besides reduced engine wear, more oil in the crankcase for long term storage.
This is a cause for concern if I was going to store a saw for any length of time, I'm now thinking fogging will be mandatory.
It seems so little oil was left in the crank of that saw, yet there is no scoring and it would be fine with just a new ring. Or perhaps this is carbon from blow by that has hardened over time and the oil loosened it up? It did have some carbon stains in the crankcase.
Maybe that extra bit of oil at 40:1 vs 50:1 will have another benefit besides reduced engine wear, more oil in the crankcase for long term storage.
I've taken apart engines that I knew hadn't run in years and years that still had oily residue. It seems to me that oil doesn't as much dry up as it does "leech" away into anything porous, or turn into a black coating mixed with dust.
There is also a difference in the way some synthetic oils dry versus mineral oils. Some of the synthetics dry to nearly a wax type substance
Extra residual oil is another very good reason to use a bit more oil.
I use fogging oil in all my stuff if it will be not used for an extended period of time.
That waxy substance is typically found when ester based oils break down, which they rapidly do in the presence of water and 02. Esters are actually made by reacting a acid with a fatty molecule of some sort, so the residue you noted makes sense.
Wow , almost as bad as Echo's reputation for factory lean condition . That's brutal !
To add to the answers of oil ratios, I use 25:1 100LL/Maxima K2 in my 3120xp and 30:1 in my smaller stihls.
I've had to switch carbs in the 3120xp to a WB37 with some modifications so that I can adjust the high-speed circuit. WB37 doesn't come with a choke, so use a fabbed linkage to prime the diaphragm. Works really well. Operating at about 1000'-4000' msl at density-altitudes of (-)100' through (+)6000', depending on weather conditions, so careful carb-tuning each day is a prerequisite to a happy engine. Pistons always appear bright and clean, top and bottom... obviously because it's running cool. I've done some tame porting mods to the 3120xp -- trimmed the base so compression is up to around a true 10:1; squish is tight at around 0.30mm, lower transfers opened and radiused for good flow; transfer tunnels smoothed and polished (kinda). Merely widened the exhaust port, upper transfers, and intake port a bit. Unlimited coil retarded by 12 degrees makes for easy starts and tons of power over 8500 rpm. Fabbed custom exhaust. Lightened and flowed piston; coned piston-pin ends. Balanced crank/rod/piston assembly. Try to keep her below 12,000 rpm. Runs like a raped ape, but super-smooth. A real pleasure to handle.
I've had to switch carbs in the 3120xp to a WB37 with some modifications so that I can adjust the high-speed circuit. WB37 doesn't come with a choke, so use a fabbed linkage to prime the diaphragm. Works really well. Operating at about 1000'-4000' msl at density-altitudes of (-)100' through (+)6000', depending on weather conditions, so careful carb-tuning each day is a prerequisite to a happy engine. Pistons always appear bright and clean, top and bottom... obviously because it's running cool. I've done some tame porting mods to the 3120xp -- trimmed the base so compression is up to around a true 10:1; squish is tight at around 0.30mm, lower transfers opened and radiused for good flow; transfer tunnels smoothed and polished (kinda). Merely widened the exhaust port, upper transfers, and intake port a bit. Unlimited coil retarded by 12 degrees makes for easy starts and tons of power over 8500 rpm. Fabbed custom exhaust. Lightened and flowed piston; coned piston-pin ends. Balanced crank/rod/piston assembly. Try to keep her below 12,000 rpm. Runs like a raped ape, but super-smooth. A real pleasure to handle.
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