Fuel Mixture Supporting evidence for 2-stroke oil/fuel ratio

[Fabian]

G'day all

Just a quick note for the banter going on about what oil/fuel ratio is best.
I've written up some of my ideas on the best ratio for the issues we have to deal with on our 2-stroke Chinese Bicycle Motors.

I firmly (and with good supporting evidence as listed in previous post) use plain old 2-stroke mineral at 20:1.

Doing some research i came accross a castor oil fortified 2-stroke oil listing the oil/fuel ratios for various applications.
In the world of lubrication, nothing gets any better than straight degummed, first pressing castor oil for maximum tolerance to heat and pressure.

This product (similar to others) is a blend of castor and synthetic but when the going gets tough, it's the castor giving you the real protection.
Scroll down to the bottom of the page and look at the oil/fuel specifications.
Since our bicycle motors are air cooled and small capacity, they most closely fit the "Kart" specification.

My goodness, they recomend 20:1 and that's with the extra protection of castor oil.

Naturally, everyone will have their own opinion
Still, it's food for thought before you try and run your Chinese Bicycle Engine engine on 40:1 or worse, a nightmarish 50:1 just because the oil container says it is recomended for use at 50:1

http://www.klotzlube.com/techsheet.asp?ID=2

Cheers Fabian

 

[Pablo]

But you offer no proof that the correct oil at 50:1 in a normally loaded MB engine does harm. (because it doesn't).

I have nothing against Klotz - good stuff - but what about all the guys zipping around with 100:1? (And I am NOT just talking about Amsoil, Opti guys!) - however to use an advertisement as your backing (while stating this is the best oil with castor, etc) is no different than someone reading a bottle and saying "yep 50:1".

I'm not posting to say 20:1 is bad or to say 100:1 is bad or 32:1 is bad.

What I AM saying - use what works and a great starting place IS what the oil manufacturer recommends.

BTW - I use Amsoil Racing oil (Dominator) with my own castor oil added. Not near as dirty as Benol.

 

[Fabian]

Yes Paul

You make a very good point: quote "But you offer no proof that the correct oil at 50:1 in a normally loaded MB engine does harm. (because it doesn't)."
I am certainly not advocating one manufacturer of oil over another - just that they had a website listing recomended oil/fuel ratios with a castor fortified oil.
I use mineral based 2-stroke oil at 20:1 with great results - when i used 25:1 the results were not so good.

Using the SickBikeParts Jackshaft system the only throttle position the bike ever sees is 'Wide Open Throttle'.
As soon as the bike hits 3500 rpm i change up a gear and run full throttle, change gear, run full throttle, change down a gear for a hill, run full throttle, maintaining the best speed i can squeeze out of the motor.
With the trailer attached, i'm really squeezing the motor for all it can give.

The bike never sees anything other than wide open throttle.

I will agree that if you are just tootling around, hardly ever using wide open throttle, you can get away with leaner oil/fuel ratios.
From my experience though, there is only one throttle position - Wide Open Throttle as you can't get enough power at any other throttle position, so i'm coming from a perspective where the engine never gets a rest; it runs hard from the moment it is warmed up till the trip is over, sometimes being a 3 hour trip with in situ refuel.

I've posted plenty of supporting evidence in another thread and there's enough data if it needs to be researched and verified; a good education in 2-stroke lubrication and fueling requirements presents itself when involved in Karting where the top guys extract every last little drop of performance out of those 2-stroke engines and in the search for that little bit extra, sometimes experimenting with friction welding internal components.

Fabian

 

[Pablo]

I was not talking about YOUR application. Pulling a trailer, up hill, at WOT - well 20:1 is fine. I thought I was fairly clear that I was speaking to a larger audience than just you.

All I see is a link to Benol, and yes I have read all the 10:1, 15:1 "studies" - but those guys actually adjust their fuel/air mixes for conditions, include fuel/oil ratio. What other supporting evidence did you post? I'm not trying to be a wise guy. I can distinctly say every MB meet I have been to, there is a VAST difference between what those engines see and a racing kart engines see! Huge, really. Again - your application may even be WORSE than a kart, but recommending folks will automatically get better protection at 20:1 is a bit broad for my tastes.

 

[Fabian]

You have a completely valid point Paul.

I have no reason to disagree - your logic is sound based on variability of operating requirements that my application never gets to see.

My experience though is that there's only one throttle position for these little Chinese engines - Wide Open Throttle, trying to squeeze on them everything you can get, whilst keeping the rpms less than 3500.
To do that though, you need a Jackshaft Shift Kit.

Fabian

 

[oldsalt]

Why would a mixture leaner in oil than, say, 36:1 be desirable? Unless of course it's a competition engine that needs to have its high octane fuel as unadultarated as possible. The oil seriously lowers the rating. Maybe for economy? But the math seems to say that a 50 cc engine operating 100 miles per month will save cents, not dollars, in operating cost. The only other reason I can think of is the plug fouling issue. But that's a red herring. Since the early '60s modern two cycle oil has vertually eliminated that problem. That was a problem back in the loop scavaged, baffled-piston days, but not now. BTW. I use 20 or 24:1 in every two cycle I own.

 

[Fabian]

Exactly, oldsalt

There is nothing desirable about lean oil/fuel ratios except for emissions reasons or trying to extract the last once of power out of a precission engineered liquid cooled 2-stroke racing engine.

Over and over again, the issue of hydrodynamic piston ring seal through an oil barrier is widely overlooked, especially in an air cooled engine manufactured with poor engineering standards.

It's got far less to do with engine protection and more to do with maintaining combustion presssure as the rings pass over areas of localised bore distortion caused by significant temperature variation and metalurgy that isn't the image of perfection.
Having said that, oil absorbs heat and helps control temperature variation - running overly lean oil/fuel ratios robs you of this critical aspect regarding thermal stability in the cylinder bore area, especially on the exhaust side.

These debates will contine - it's the nature of human emotion over riding logical analysis by science.

Fabian

 

[Pablo]

I really can't argue with that logic.

I won't even try to override science - BUT there is nothing WRONG with a street MB in a moderate climate with a 180# person with a standard engine running a good oil at 32:1 or somewhat leaner. He will see no excess wear, lose no power, etc......especially when everyone is trying to shut 2 strokes down for emissions.

Use the ratio that is correct for your conditions!

 

[Fabian]

That's good logic Paul: quote "Use the ratio that is correct for your conditions!"

I would never go against this reasoning - if you are just tootling around, in areas of pedestrian traffic, using maybe 1/4 throttle and never running periods of wide open throttle, 20:1 would not be of any advantage; just making excessive smoke and irritating people around you.

I will say this though, using 20:1 in my application of constant wide open throttle, the engine never smokes when under load.
It will however smoke somewhat when idling at a set of traffic lights and when taking off from traffic lights till the crankcase has been purged from settled oil, whilst idling at the lights.
Typically, i time my way to a set of lights so the lights have gone green when i get there.

Fabian

 

[motorpsycho]

why is it then, that my 2 stroke weedeater recomends 40:1, my 2 stroke chain saw recomends 40:1 and the instructions for my 2 stroke bicycle motor recomends 40:1(after break in)? every 2 stroke that i have ever dealt with says to run at 40:1. my father in laws 40 h.p. outboard also recomends 40:1.
I have been running my weedeater at 40:1 for 15 years...maybe 40:1 was the suggested ratio at the time that it was made? my chain saw is about 8 years old...and i still run it at 40:1. My bike motor was built jan 2009, and it says right in the instructions to run it at 40:1 as well.
A bunch of people say that 40:1 is too lean.
so.....who's right and who's wrong?