yet another oil thread

[GMP]

IMO, one word, EMISSIONS. Same reason their OI is programmed so stingy.

It has been proven on a dyno more oil = more power down to 16:1 as long as jetting is corrected. Migration tests Maxima did with radioactive tagged oil showed optimum ratio for a 250 to be about 36:1. This weekend we did a 24hr team race. My bike ran about 7 hrs of those, with just a small damp ring around the silencer opening. 36:1 Dominator. Bike has over 160 hrs now on original top end and runs hard like new.

[mattc82]

Thanks. What, if any negative effects are caused by running with a little more oil say 40:1 vs 60:1? Maybe a little more crude out the muffler?

[GMP]

IMO, none. When I pull my motor down at the end of the year I will make it a point to take some pics. From nothing but positive experience over the years, no one will convince me that leaner is better as far as oil ratio, but it will always be up for debate thats for sure.

[ricoyam]

I'm of a differing opinion. I run Optimol 2 at 100:1. I've been running it for 15 years in a variety of 2T's, air cooled, liquid cooled, 50cc up to 402cc. Unlike Glenn I don't pull top ends every season. I only do it if there is a failure or wear is evident. I've not had a failure or any notable engine wear in those 15 years. I have a 1998 KTM 200 EXC that has never had the head off and still runs crisp and quiet. I don't foul plugs and have no spooge although with the lean oil ratio my bikes tend to run rich on the bottom. A problem of not being able to get pilot jets lean enough.

I think you should just find an oil you like and stick with it. Guys that change oils every 2-3 years never really know if what they're running is good or bad.

The last 2T I had to do any top end work on was the Bonneville Streamliner I crewed on. It was a Aprilia 50. Over the time we ran it we tried methanol, nitrous, nitro-methane but set the record running a turbo with methanol. We ran a 36:1 mix with 927 because of its castor base and good mix ability with alcohol. With nitrous we could barely get two runs out of it and never did get back to back record runs. We were getting in excess of 24hp out of it with a rev limiter set at 14,500rpm. What this taught me is top end seizures have less to do with oil and more to do with the fuel and the burning characteristics.

[lodcomm]

Thanks. What, if any negative effects are caused by running with a little more oil say 40:1 vs 60:1? Maybe a little more crude out the muffler?

Bear in mind that running a Higher oil to fuel ratio (i.e. 30:1 instead of 50:1) will result in a leaner fuel mixture, and may result in the negative effect of your engine running hotter. Your absolute best bet for protection and performance is to run your pre-mix according to the bike manufacturers spec, and jet your bike for that mixture and your local elevation & ambient temps. any of the modern synthetic oils are designed to work perfectly at the 50:1 or 60:1 most manufacturers spec for synthetics these days.


heres jeff slavens take on 2T oils:

https://youtu.be/tcSDNZohzfM

[GMP]

My top end is original, over two years old now. I do take a peak in the port now and then to see how things look and they look great.
Compare these two ratios. 50:1 = 2%, 36:1 = 2.7%. Thats a -.7% difference in fuel mass through the carb, or .7% leaner all else being equal. Using the main jet for an example, and assuming the numbering scale of Keihin brass is linear at least in a narrow range of interest, that would mean an equivalent of .7% smaller main jet for the richer oil mix. So, if you current main is #162, it would be like leaning the bike way out with a #160.9, if you could get one. Am I worried? I would think normal unaccounted for environmental variables have much more effect.

[nevermind]

My top end is original, over two years old now. I do take a peak in the port now and then to see how things look and they look great.

Glenn,

What mix ratio are you running?

[GMP]

36:1, based on several factors. Its also a good mix to share with a 125 as I do occasionally, and when we would go on trips I would cut it 50/50 with straight gas for my wife's GG Pampera(trials motor).

[Gibnut]

I know this is an older thread and much of it is subjective however I am curious why the Beta owner's manual calls out a 1.6% ratio on mixing which equates to about 68:1.

Any thoughts here?

Probably because modern full syn 2-t oils are very good at lubricating and the stock jetting is pretty rich.

FWIW, I run 98 octane/Motorex full syn @ 50/1 in the 250 with (back to) stock jetting - no spooge & runs great.