50:1 fuel in 40:1 machine

[IndyIan]

Originally Posted By: Shannow
If somehow the hydrocarbon oil replaced gasoline, and escaped combustion entirely...the premise that oil leans you out and melts pistons is farcical.

Well, how is it making the exhaust damp on your OPE then? Some oil must escape combustion. Try running 20:1 for a tank, you will see that more oil ends up on your exhaust. I doubt you'll melt a piston unless your motor is running quite lean at 50:1, but in some cases, 2-3% less gas by volume may make a difference.

 

[PhilsSmallEngine]

It's a McCulloch. It was one of the cheapest trimmers on the market. It will burn anything combustible and it will be lubricated by anything oily. 40:1 or 50:1 won't make a lick of difference. Does anyone really think that .6oz of a high quality oil distributed over a gallon of gasoline makes even the slightest difference on a McCulloch machine or really any 2-cycle small engine? That oil represents a meager ~0.47% of the 1 gallon for you math hounds.

 

[Shannow]

Originally Posted By: IndyIan
Originally Posted By: Shannow
If somehow the hydrocarbon oil replaced gasoline, and escaped combustion entirely...the premise that oil leans you out and melts pistons is farcical.

Well, how is it making the exhaust damp on your OPE then? Some oil must escape combustion. Try running 20:1 for a tank, you will see that more oil ends up on your exhaust. I doubt you'll melt a piston unless your motor is running quite lean at 50:1, but in some cases, 2-3% less gas by volume may make a difference.


Clearly,
* the oil that is in the middle of the cylinder/chamber is not lubricating anything...it is there burning, as part of the hydrocarbon that is reacting with the oxygen...it's not leaning the air/fuel out and burning pistons.
* The only oil doing the lubricating is in the fuel/oil that is in contact with, "sticks to", and wets the wall...a tiny fraction of what oil was in the chamber...it, and any fuel that was still unevaporated from it doesn't burn due to the closeness of the flame to the relatively cool wall.

The "wetness" of the oil dampens the carbon in the exhaust.

Mercedes used an oil drip feed on their wankels to ensure that a wet film made it along the inlet manifold port to lubricate apex seals without filling the chamber full of octane reducing lubricant that wasn't lubricating anything.

 

[bubbatime]

For what its worth, I had a trimmer that called for 40:1. All my other equipment was 50:1, so I decided to just run 50:1 in everything.

It flat out ran terribly on 50:1. I tried every carb adjustment I could and it still wouldn't run right. Went back to 40:1 and it ran like new again.

 

[Mike72]

Originally Posted By: PhilsSmallEngine
It's a McCulloch. It was one of the cheapest trimmers on the market. It will burn anything combustible and it will be lubricated by anything oily. 40:1 or 50:1 won't make a lick of difference. Does anyone really think that .6oz of a high quality oil distributed over a gallon of gasoline makes even the slightest difference on a McCulloch machine or really any 2-cycle small engine? That oil represents a meager ~0.47% of the 1 gallon for you math hounds.


It's splitting hairs but It will make a slight difference over time. With the additional .6oz in the 40:1 versus the 50:1 mix,there will be slightly more oil build up in the crankcase and slightly more deposits in the exhaust ports and muffler.
With a two cycle engine,any amount of oil added to the fuel in a mix ratio must eventually pass through the combustion chamber, and in a ideal situation, most of the oil will burn with the fuel and leave a minimum of deposits.

 

[PhilsSmallEngine]

The reality is that through gasoline evaporation, the ratio will vary no matter what you attempt to do. The Stihl oil is more than good enough to provide the same, if not significantly better protection at 50:1 than the bog standard non-synthetic 2 cycle oils at 40:1 that machine was designed to run on in the 80s-early 90s.

 

[lars11]

Good for you that it recovered, but the case sounds completely unreasonable. Generally, 2 or 2.5% will work perfectly in most small OPE. If you want to mix just one can of fuel and you have both requirements, just choose one ratio. I would choose 2% but you could just as well go 2.5%, none of your ope will fry. With some oils, you could go to 1 or 1.5% even.
For best performance you may want to adjust carbs, but that's something you may have to do anyways due to different gas characteristics between cans. If your ope have stupid locks or difficult screws on carbs (EPA etc), remove them and ajust anyways.
Originally Posted By: bubbatime
For what its worth, I had a trimmer that called for 40:1. All my other equipment was 50:1, so I decided to just run 50:1 in everything.

It flat out ran terribly on 50:1. I tried every carb adjustment I could and it still wouldn't run right. Went back to 40:1 and it ran like new again.

 

[Jakegday]

great input guys. very much appreciated. Although im now wondering, what does OPE stand for?
After using my new trimmer a couple times, i cant see myself ever picking up the mcculloch again (unless of course this new one breaks down) so i just prepared it for storage, and put it away. My new husqvarna blower/vac also uses 50:1, so i lucked out there!
Again, thanks guys. This has been a good read.

 

[Michael_P]

OPE: Outdoor Power Equipment