Let's Talk 2 Strokes

[Nate Surveyor]

If you are running a oil injection system, and you delete the oil injector, and pre-mix the gas, then the fuel you run is THICKER than straight gas.
The closer to 20:1 you get, the thicker it gets. (20:1 is the richest we have run)
So, you have to OPEN up the carb, and let more gas through it, the richer you get with oil.
If you are all jetted up for running 50:1, and you suddenly run 32:1, you could go too lean, and burn up the motor, due to a lean condition. Caused by the THICKER (more viscous) mix.

So, when you settle on a mix ratio, and have everything tweeked up right, then you get somebody else's pre mix, that is another ratio, you can have trouble.

Same thing can happen if you are jetted for 32:1, and then you run 50:1, it can run too rich, (juicy) and now you foul the plugs.

Anywhays!

Remember the viscosity of your fuel!

Nate

 

[seadoosnipe]

Viscosity?

Nate, I don't think I"ve ever heard it quite explained that way before. I don't know if that applies. Viscosity is weight by specific gravity, not by mix. Although, mix will affect the weight of specific gravity.

Our Seadoo's run on a variable rate, oil injection pump. Which means, at idle or slower speeds, the engines oil requirements are less, since the amount of heat created by friction is not that great. At this point, the rate injection pump may be pumping a ratio of 50:1 . But when we speed the engine up, we start creating more shaft torque and friction on the bearing surfaces. Our oiling requirements change. We need to add more oil to the fuel, so by the time your at WOT, the oil ratio may be as high as 32:1.

Remember, 50:1 has less of an oil mix than 32:1. The ratio is 50 parts fuel to 1 part oil. So, the higher the first number, the less amount of oil is actually contained in the fuel by the second number.

In the term viscosity, most think about the properities of oil. In a 10-30 weight oil, its specific gravity when cold is about 30 weight, but as the oil heats up, the viscosity breaks down to a specific gravity weight of 10. The same is true in a 90 wt gear oil. It's specific gravity by weight is 90. When heated, it retains the same weight. Though, you can buy a 75-90 gear oil, which means, when heated, it breaks down to a specific gravity of 75.

Since the primary purpose of oil is to carry away heat from the bearings created by friction, the purpose of weight (viscosity) set up by the manafacturer is to decide how long that oil needs to remain on the bearing during it's pass. Oil with a higher weight will remain with the bearing longer than one with a lower weight.

This has bee a topic of debate about 6 months ago. You missed a good debate. If you like, you can use the search engine above with keywords like "oil debate" and see what you come up with. I remember Robin Savell Lloyd and Dennis was part of it..................:cheers:

 

[Nate Surveyor]

Thanks Snipe

Some of that stuff about variable rate oil feed, I did not know.

Also, the exact meaning of "Viscosity".

But, we weren't exactly professionals either!

We were working with the practical side of the thickness of the mix, whatever the nomenclature.

But, the general look at the subject sure made some fast bikes, and alot of fun!

Nate