Gas oil ratio question

[weimedog]

Still 32:1 after all these years....since I always run 32:1, and I always stay on top of the tuning I never have to "re-tune" because i have no intention to changing until I see a reason to do so. One thing I can say...theoretically..a racing two stroke might generate slightly less "flash" peak HP with the heavier oil mixes, but at the end of a race they will have lost less than those pushing the edge in mixtures with less oil. AND I can tell you they last longer over a season than those with less oil in the fuel. Part of the reason earlier synthetics wanted to be a 50:1 was first a marketing deal and second, they didn't burn as clean as the products they were replacing and would make a mess of the exhaust...now they have improved to the point they burn cleaner than the old non synthetics as well as out perform them in higher heat & shear situations. My feeling is the power you might loss with the more oil is gained thru less losses due to heat and friction over the period of a race. Wish there was numbers to back that up...but my seat of the pants during the races when I was doing that and my eyes evaluating tear downs have pushed me to ..not change from the 32:1....in motorcycles and now in saws.

[Al_Smith]

Once again I'm kind of like Walter in the fact I see no reason to change either .Evidently most of the hotsaw guys don't either because they mostly run higher grade oils at----32 to 1 -----  ;D I figure if it's good enough for a 5,000 dollar hotsaw it's good enough for me .

[stump farmer]

I've always run 40:1 thinking that I've built in a little buffer for safety due to the elevation differences I work at: sea level to 10K+. Smalldog's point is making me re-think that, I do follow what you're saying with the less fuel=leaner due to more oil in the mix. And yes my saws do feel lean at low elevations. Good info, thanks.

[Al_Smith]

If you tuned them for 10,000 they would be lean a couple thousand lower .Conversely tuned at sea level then going to 10 thou they'd likely blow black smoke .

[stump farmer]

They get tuned around 2k and I've been limiting the high rpm to 12500 (stihl 460) in the hope of again having a buffer. Trading some performance for reliability I hope. I'm looking for a setting that will work well enough for all elevations. I won't allow anyone on the crew to field adjust the saws as it usually results in a seized saw. Those little orange handled screwdrivers are locked away. This has been working OK, but I'm always looking for something better. Never thought that using more oil could lean the saw.

[Al_Smith]

 :D It doesn't lean the saw .That's taking one persons opinion and discounting 100 others .Besides 40 to one is an accepted ratio .

Well then ,take junker of a saw and run it at 80 to one and document exactly how that works out for you .

[stump farmer]

Realize it's an opinion, but an interesting one at that.

[Al_Smith]

Okay ,let's look at it in a different perspective .When you run any engine with too much air in the mix it runs lean .Lean ratios of fuel  to air  burn faster which also equates to hotter .Now because some type of oil is required in the fuel mixture for two cycles it would effectively lower the heat generted by the combustion of the fuel merely because it lowers the burn rate .Plus the fact it gives lubrication to the vital components of the engine ,most important .

So that said that fuel and oil ratio will remain the same no matter if the saw is at the top of Pikes Peak or in Virginia Beach Va at sea level .The only thing that needs changed is the adjustable carb jets to effectively change the fuel to air ratio .

Now a modern automobile does this all by itself using the ECM or engine control model but a chainsaw isn't quit that smart yet,you have to adjust them .

Oh alas ,I'm fighting a loosing battle .

[John Mc]

Example: a 40:1 mix will have twice the fuel in the air/fuel mix as will a 20:1 mix because the extra oil is not taken into account for air/fuel mix calculations.

No. 40:1 will have slightly more fuel, but no where near twice the fuel. The % fuel in 40:1 is 40/41=97.6% gas. In a 20:1 mix, it's 20/21=95.2% gas. A pretty small variation, which might just be overshadowed by altitude or temperature variation. The difference in % of Gas between 40:1 and 50:1 is s

Another question: how much does outside air temperature affect the air/fuel ratio? At 120 degrees the air should be thinner that at 40 degrees. The colder air is denser which will richen up the mixture.

Denser, colder air will make the mixture leaner, not richer (more air per unit volume).

[stump farmer]

Thanks for setting me straight. That post was all wrong.  :-[

[John Mc]

No problem. I get it backwards myself half the time.

[smalldog]

Opinion of one??? I take it you didn't search the subject then.  Whatever.......

[SPIKER]

There were a good number of inject-able oil engines back in the late '70's when they were coming out.   I have a '77 Kawasaki 440 snowmobile setting out back with it on , though I mix it rather than depend on the injection function properly.   Also had a RD350 Yamaha street bike circa 84 that was I think a '76 vintage bike.  That was a ride pretty much the first crock rocket ;)   Bright orange with black stripes.

Like others mentioned Mix is less important than the Oil brand recommendations from what I have read learned through past.  Oil in the mix is only partly burned so it displaces gas and a slight lean condition could develop but at such a low rate that a 1/4 turn on the A.F. screw or dirty filter is a bigger problem than the oil change from 40:1 to 50:1 will make.   The rich oil mix will also raise the octane rating of the fuel slightly as it lowers temp & ignition point of the fuel during high speed running.   Some types of oil also burn less than others and can foul exhaust system and carbon up or foul plugs which also increases compression ratio on small engines that are often in the 13~14:1 compression already slight build up can effect pre-ignition detonation which is also where overheating & melt downs can happen when running low octane blends.   Toss in the 10% or more ethanol in most fuels today and you can really bugger up a small 2 cycle engine which is why there is some legal pressures to NOT push the E15/E85 stuff the EPA has mandated for 08 & up cars.

Mark

[tyb525]

All 2-stroke engines require oil. Oil is their lifeblood, because without it, they wouldn't run for long.

Historically, running a mix richer in oil, such as 30:1, has been successful since day one.

Sure, technically 30:1 will be "leaner" than 80:1. BUT that does NOT mean it is getting less oil! Failure from running lean is due to heat and lack of lubrication. The oil has the ability to cool AND lubricate.

SO, running a mix of 80:1 simply means you must burn more mix in order to get equal lubrication. You will use the same amount of gas, but now where is the lubrication (oil)? It is reduced.

Is reduced lubrication ever a good thing in an engine of any sort? Would you run 0w20 oil in your diesel, or mix your lawnmower's engine oil 50% gas and 50% engine oil to thin it out in order to use less oil?

Sure, they might run okay for a little while, but what about long term? What about when the engine really gets pushed, or you forget to change the oil for awhile? Since you were really toeing the line of proper lubrication from the start, what now?

Just because you can run your saw with 80:1, why risk it? Have you done rigorous tests with all saws to make sure they can stand up to that? You're really pushing the envelope running mix with that little amount of oil.

At what ratio is there too little oil? When you reach straight gas?

[Al_Smith]

Sure, technically 30:1 will be "leaner" than 80:1. BUT that does NOT mean it is getting less oil! Failure from running lean is due to heat and lack of lubrication. The oil has the ability to cool AND lubricate.

  At what ratio is there too little oil? When you reach straight gas?

Thank you ,that's the point I was trying to make all along but with little success .

[weimedog]

And to add a little fuel to the fire..when you tune your saw, you are basically tuning the burnable fuel to air ratio...not the oil air ratio. And while you may have to tweak from one mixture to the next assuming someone randomly changed the oil gas ratio's I have found the difference between 40:1 and 32:1 to be small enough that when I run short on fuel, my friends 40:1 mix work fine..usually without the need to change anything...it has happened..not often.

I guess another way to look at it is you tune with your hi and low speed adjustments until you get the the right volume of fuel...the oil goes along for the ride. And yes those screws might be turned out a little more to accommodate the additional volume of oil. But its a bit backward to think the oil is leaning out the mixture...and as was said in many ways before, there are lots of additional benefits to having a bit more oil than less....still 32:1 after all these years...and everytime I tear a saw or motorcycle down (Like last week's Jonsered 820) that has time on it..the more empirical evidence is telling me not to change...

[clww]

I run 32:1.
No discussion :D :D

[Just Me]

Try as I might I can't get through my 2 inch thick scull why anybody would run a saw at half throttle for very long  ???

Log home work. I have a couple of Husky 142's with crosscut and rip chains that I use, and there are many times I have to be cautious not to make a costly mistake, so I run mid throttle.

That being said, I run synthetic, have since the 70's, but at 32-1. I have those two saws tuned to run well in the middle, and I do have to change plugs more often, but they serve me well.

I am a firm believer in synthetics. We had a smashed radiator on our race truck at Crandon, finished the race and the gauge was pegged the last two laps, gauge went to 350 degrees but we have no idea how hot it actually was, just over 350. At the finish line it was so hot it burst into flames when it stopped, motor siezed immediately. After it cooled down, the motor restarted and was able to finish the race the next day, although a tad down on power. When torn down there was some ring damage and scuffing of the cylinders but the rod and main bearings were fine. Amazing.

I use it in everything that is expected to work hard, from cement mixer to tractor.

Someone mentioned a Yamaha RD 350. I had one of those for years set up for road racing just to play with with a full engine build. Bad fast! It would beat my 1000 Kawasaki up to its 120 mph top end. I can't imagine how Enderle won Daytona with one though as my hand were so numb after 10 miles that I couldn't feel the bars. It was fun, but the local constabulary told me the next time they caught me on the street I was going to jail. Had to let it go..... :(

[smalldog]

This is just too funny!

This is what I said 17 posts ago: All I'm saying is the premix ratio affects jetting. If you want, Google "premix affects jetting" and read for your self.

I never said less oil is better. I did say that if you have a newer EPA saw that is quite lean to begin with, increasing the oil in your premix WILL lean it out further. Just adjust your carb for the new mix.

Now, I never stated what ratio I run, I never said that I think people should run a specific ratio.

I have converted many sleds, cycles, and atv's from oil injection to premix. Many of them were for people that raced. The newer ones were Yamaha RZ350 cycles and the 350 Banshee ATV's. In those cases, going from zero premix (injection)and going to say a 32:1 ratio, will have to increase the size of the carb jets to allow for the volume of oil that is now flowing through them.

I don't care what brand oil, at what ratio or what brand saws you run, my only point is: if you change the percent of oil going through the jets of your carb, you are also changing the amount of gas going through.

Yes, the Yamaha RD bikes were good bikes. I've worked on many on my own and at the dealer. I personally had  '70,'72,'73 Kawasaki 500 triples and a nasty '72 H2 750 triple with milled heads and chambers.

[smalldog]

Yes, if you have a older saw you will have nice big carb jets and fuel screws. Some modern EPA saws (most are non pro saws) are coming with either restricted adjustable screws or no screws at all. Many have pressed in jets in the carbs. I all ready went through this back in the 1980's and 1990's with motorcycles, snowmobiles, and ATV's at the dealer. This is going to get much worse before it gets better. Fuel injection helped everything from auto's to snowmobiles as far as the lean EPA standards went. What will happen with chainsaws? Fuel injection or 4-strokes? Definitely more weight.

[screwman]

Yes, the Yamaha RD bikes were good bikes. I've worked on many on my own and at the dealer. I personally had  '70,'72,'73 Kawasaki 500 triples and a nasty '72 H2 750 triple with milled heads and chambers

Wow, man, those things were downright scary.

[weimedog]

Yes, if you have a older saw you will have nice big carb jets and fuel screws. Some modern EPA saws (most are non pro saws) are coming with either restricted adjustable screws or no screws at all. Many have pressed in jets in the carbs. I all ready went through this back in the 1980's and 1990's with motorcycles, snowmobiles, and ATV's at the dealer. This is going to get much worse before it gets better. Fuel injection helped everything from auto's to snowmobiles as far as the lean EPA standards went. What will happen with chainsaws? Fuel injection or 4-strokes? Definitely more weight.

I'm betting on battery less fuel injection systems like on the new four stroke motocrossers. That with some level of ignition & fuel curve control as on those race bikes as well. A whole new area for those who like to tinker to play...and before folks cry about the concept...look at model railroading, race bikes, race quads and a whole host of other area's where the interface of cyber tech and the control systems of mechanical systems generated entire new places to hack around. I'm looking forward to it and I really don't think weight will be as much of an issue as the technology evolves...anymore than it is with the two wheeled world.

[Just Me]

Yes, if you have a older saw you will have nice big carb jets and fuel screws. Some modern EPA saws (most are non pro saws) are coming with either restricted adjustable screws or no screws at all. Many have pressed in jets in the carbs. I all ready went through this back in the 1980's and 1990's with motorcycles, snowmobiles, and ATV's at the dealer. This is going to get much worse before it gets better. Fuel injection helped everything from auto's to snowmobiles as far as the lean EPA standards went. What will happen with chainsaws? Fuel injection or 4-strokes? Definitely more weight.

I'm betting on battery less fuel injection systems like on the new four stroke motocrossers. That with some level of ignition & fuel curve control as on those race bikes as well. A whole new area for those who like to tinker to play...and before folks cry about the concept...look at model railroading, race bikes, race quads and a whole host of other area's where the interface of cyber tech and the control systems of mechanical systems generated entire new places to hack around. I'm looking forward to it and I really don't think weight will be as much of an issue as the technology evolves...anymore than it is with the two wheeled world.

I have to agree. In 1973 I had a 125 Suzuki TM 125 2 stroke motocrosser that weighed 212 dry. It had about 7 inches of travel and that was about all it had, Fast in its day, but not even a good play bike by todays standards. After that bike they started picking up weight as they picked up travel.

Fast forward to 2004, I bought a KTM EXC 450. Had a Bad 450, 12.5 inches of very controllable/adjustable travel, brakes that worked, did I mention a 4 stroke, six speed tranny, and it had lights and electric start. Weighed in at 252 pounds, but it felt ever so much lighter that the TM. KTM has a two stroke 250 with electric start at just over 220, and a whole lot more bike in that 8 pound difference.

The EPA is up our Heineys on every front, so it is only a matter of time before the mandate the use of FI, or make emission restrictions that can only be passed by a FI motor. Not necessarily a bad thing, but the cost of saws will go up.

I cant make up my mind if I should buy a 345XP or a 357XP. Maybe I should buy both, then I'll be set till I'm old and gray. Oh wait, I'm already gray........

[Al_Smith]

Yes, if you have a older saw you will have nice big carb jets and fuel screws. Some modern EPA saws (most are non pro saws) are coming with either restricted adjustable screws or no screws at all. 

Okay maybe for consumer saws and those not really adept at saw tuning .However keep in mind that some of us do not fit in that catagory .Besides that, they  as they might  still haven't figured out how to make a carb we can't fiddle with .If they think they can,bring it on .If we can't tweek it we'll just change it out to one we can and keep the mix ratio we already have . 8)

.

[John Mc]

I cant make up my mind if I should buy a 345XP or a 357XP. Maybe I should buy both, then I'll be set till I'm old and gray. Oh wait, I'm already gray........

Did you mean the 346XP?

BTW... Husky has a replacement for the 357XP in the works... The 560 or 562XP. From what I've read here, it sounds like quite a saw.