2 Stroke engine oil observation

Larry Trotter

Larry Trotter

Well-Known Member
I have had this bike running in Arizona for about 3 years now. Built on a 200C fixi/free wheel frame from Big 5 Sporting Goods, about a $90.00 bike. Put a wheel and forks from a Roadmaster on the front to get some of the bumps out of the ride and life is good. In the past I have always used synthedic chain saw oil at about 30 to 1. This year I could only find some regular chainsaw oil in a little bigger bottle when I needed to mix some gas after the summer. Mixed this up at 20 to 1 just to be safe. Now the bike is quite a bit faster than it was using the synthedic, it will hit 32.5 on the flat when before it would top out at 27.5mph. Both are faster than is really comfortable but nice to be able to do. Nothing else but the oil has changed. I am thinking the regular oil may burn a little better then the synthedic stuff so it makes the engine a little happier? Don't know but someone else may have had similar experience with reg vers syn oil? Larry
B4.JPG
 
Larry it sounds like with the increase in oil you leaned the fuel to air mixture, you probably could have got the same speed at 30/1 with a smaller jet using the other oil. If it runs good and doesn't drip a lot of oil have fun.
 
It may not seem that the fuel mixture is thicker to the eye but 20/1 will be harder to draw through the jet resulting in less fuel in the mix going into the cylinder. I have been able to gain several mph with just smaller jets, just about every bike I've built has been on the Rich side as they came.
 
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Well I get one small drip after a long run, so I am guessing things are good. I will probably just keep using this mix as it works well and is simple to remember.
 
You will find many people using different fuel to oil. 32 to 1 is by far the most common and what I used. An expansion chamber would make a big difference. I would also look at a front disc. An adapter can be used if you want to keep your current fork. At $90 any fork will be better than stock. From your picture looks like a 1" threaded headset. Still measure and google to be sure.
 
It seems counter intuitive but more oil actually leans the fuel/air ratio. Just like Greg suggested and Larry experienced. This is because oil isn't a fuel, it's a lubricant. It will burn but it doesn't add to the combustion process. When you put more oil in there's less fuel in the resulting ratio because there's oil displacing a small amount of fuel. Leaner.

I know that seems backwards and the effects are negligible, but that's what actually happens.
 
Well I drained my gas back into the can and added about half of a little bottle of syn oil to it to bring it to about 16 to one. The bike is faster now, you are right! Seems to me now that the oil ratio has really very little to do with the speed you can get and that the speed has much more to do with mixture and the oil ratio being very lean isn't really the thing that makes for better power and speed. Larry
 
Good explanation guys. Gas and oxygen make power when mixed & delivered in proper proportions. Oil lubticates and takes up space in the fuel mix (which also cools the 2 stroke internally) oil does not contribute to power directly just helps keep things running..simple no?

Rick C.
 
Well I guess that if you drop the needle one notch and it is too lean and up one is too rich you can add a little more oil and split the difference.
 
Larry Trotter said:
Well I guess that if you drop the needle one notch and it is too lean and up one is too rich you can add a little more oil and split the difference.
Click to expand...

I'd use that as an excuse or opportunity to buy a less restrictive air cleaner and/ or bump compression a little with a thinner copper head gasket add an expansion pipe & then read the chop and hopefully require running a lot richer...see where my heads at?

Rick C.
 
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