Ideal fuel mix?

[jp233]

yes Ironman, this is all true, Hello Nailhead meet Hammer. we did a lot back in the days with high performance 2-strokes motorcycle engines (making 72-80 hp in a 250cc, which translates to 288-320 hp per Liter .... which is insane). the jetting and the fuel/oil mix are different, but related. the charge has to perform a lot of functions - combust, lube, and cool. all in relation to the air.

many years ago I called Stihl about my old 028 AV Super asking them about mix - I was running 40:1 and it smoked and could coke up the muffle screen and all that. I was babying it since it was old and unknown to me, and I didn't want to destroy it. They said that even though the old manuals said 40:1 (or fatter mix when using other oils) was out-dated and the new Stihl oil can run 50:1 in all older Stihl saws. A local dealer then told me the same thing, so I switched, re-tuned the carb a bit, cleaned the muffler screen one last time for old times' sake, and it has been ripping ever since.

 

[mexicanyella]

I’ve found 32:1 to burn clean in a two-stroke with a short exhaust path (saw, trimmer) that runs revved up and loaded, like a saw or a trimmer that is actually doing some work. As long as the mixture is right.

I used to see some exhaust spooge at 32:1 on correctly-jetted two-stroke bikes, even with fast riding, but in that case you have several feet of thin wall expansion chamber exhaust system where the exhaust slows down, cools down and the unburned micro-droplets of oil can condense out onto the interior surfaces and spooge out of the stinger/silencer.

In my experience, a saw or trimmer has to do a lot of idling or low-speed/light load usage for this to happen...or it has to be set pretty rich. I have gotten several years’ hard use out of both saws and trimmers run at 32:1 with no need to clean the spark arrestor screens.

 

[jp233]

Yeah, my story was the 028 set rich, even though I was doing some bigger cutting I just didn't want to lunch the motor. That and, chances are the first time the spark arrestor screen got caked up, it had potentially never been off the saw or cleaned. So something like 20 years

 

[ironman_gq]

I’ve found 32:1 to burn clean in a two-stroke with a short exhaust path (saw, trimmer) that runs revved up and loaded, like a saw or a trimmer that is actually doing some work. As long as the mixture is right.

I used to see some exhaust spooge at 32:1 on correctly-jetted two-stroke bikes, even with fast riding, but in that case you have several feet of thin wall expansion chamber exhaust system where the exhaust slows down, cools down and the unburned micro-droplets of oil can condense out onto the interior surfaces and spooge out of the stinger/silencer.

In my experience, a saw or trimmer has to do a lot of idling or low-speed/light load usage for this to happen...or it has to be set pretty rich. I have gotten several years’ hard use out of both saws and trimmers run at 32:1 with no need to clean the spark arrestor screens.

Has a lot to do with the oil as well, some burn much cleaner than others, some hardly burn at all it seems. Good old castor in the dirtbikes was one that always seemed to leave a sticky film on anything the exhaust could touch.

 

[Huskybill]

I run 38:1 husky Xp+ oil. I have no faith in 50:1 mix. There’s a winter and summer carb adjustments depending on where we live. I found out I don’t need to touch the high speed screw in the winter setting. Just the low speed screw needs readjustment.


Did I hear two stroke motorcycles? Remember King Kenny? V4 500cc

 

[mexicanyella]

Has a lot to do with the oil as well, some burn much cleaner than others, some hardly burn at all it seems. Good old castor in the dirtbikes was one that always seemed to leave a sticky film on anything the exhaust could touch.

True. I am working my way through a pint of Klotz BēNoL mixed 32:1 (mostly because I wanted to smell some castor fumes and pretend I was still a dirt bike kid) and even after a bunch of full-throttle cutting of heavy grass in a boggy area, the port and inside of the muffler have an oil film with that stuff. The spark arrestor screen is still clean-looking, but I’ve only burned about 1-1/2 gal of that mix so far...

...smells good though! If I squint kinda funny and use my imagination, I can pretend it’s my old YZ, not a strato trimmer.

 

[jp233]

Yep. So you have a Kenny bike?? I could do one of those even though I haven't ridden on the street in 17 years. I'm specifically talking about 250 GP racebikes, mainly the venerable Yamaha TZ 250

Absolute thrill rides. 238 lbs with 2-3 lbs fuel, mine made 72 hp, zero low end power - all zing, forget it below 6-7k...... but above that esp 8-9k ---- hold onto your cookies!!

 

[Huskybill]

With some saws having bearing spinning in the bores in the case that tells me the bearings are over heating. Could the 50:1 lack of oil cause this. It seems the small saws and larger saws seem to have this problem.
Or your using old outdated mix. How often do you mix fresh mix. Two stroke mix lasts 30 days max. The oil seperates in the mix from the gas when it sits. We need to shake the can of mix before we pour it. Maybe the 50;1 mix in the can seperates and we’re running 100:1 by not shaking the can. Bearing seizures can be multiple causes.


I had a twin cylinder T500 suzuki too but I sold both streetbikes and stayed with my husky dirtbikes. My barn find, probably decades in a barn.

 

[PakProtector]

There is one more fly in the ointment; gas with ethanol and gas w/o. Ethanol requires about 2x more than gasoline, and I discovered I had to lean out my string trimmer a wee bit when I located a local source of ethanol-free. Have not yet fed any to the saws yet; I may have to close up their H jets a hair...we shall see. In any case, same 40:1 mix will be used.
cheers,
Douglas

 

[jp233]

in my saws I use ethanol-free 100% of the time unless I'm totally hosed (around here it's usually 91 octane, usually called Rec Gas or Rec 91). Down south it was Rec 90. You can generally always find it around marinas

and other yard equipment I use ethanol-free gas 98% of the time. I'll only use pump gas (i.e. up to 10% ethanol) when it is used right away in one job, and the gear won't sit for any appreciable amount of time, like a lawn mower or string trimmer (which are also both 4-chokes).

I've posted before but if anyone has lots of saws (are there people here that have lots of saws? I haven't noticed... ) , and or other 2-strokes and especially if you need to mix multiple ratios, I cannot recommend enough the Accu-Mix jug.

https://www.accu-products.com/accu-products-specialties/accu-mix-fuel-jug/prod_3016.html
This jug is fantastic, I've been using one for 17 years. Ratios 15:1, 16:1, 20:1, 25:1, 30:1, 32:1, 40:1, 50:1

Able to mix small quantities , so great for all small equipment like saws and other yard gear that is a 2-smoker.
Great caps and o-rings - mine are still original after all this time.
Mix up your fuel and mix oil, put the caps on, and shake it as hard as you want.

(OBTW each "unit" of fuel marked on this jug equates to one pound weight, depending on the fuel of course, this is a racing-inspired jug)