Mix ratios

[SupermotoFan]

Rebuild question as it relates to oil:  I thought I remebered hearing somewhere that full synthetics were not the way to go in some situations (i.e. just after a rebuild, or on a brand-new vehicle).

Can anyone confirm or deny?

P.S.  As the bike has never started under my power yet--I'm ready to sign up for the Amsoil Interceptor at a slightly cautious 80:1

Thanks!

[alan]

Check with Paul, he is the Amsoil King!

[KXcam22]

The only time to avoid synthetic is on a 4-stroke on a brand new engine or rebuild.  You must break it in before switching to synthetic or the rings will not fully seat.  I experienced this on a friends new street bike and we had to pop the cylinders off, and re-hone it.  For 2 strokes there is enough fuel wash on the cylinder walls that this is not an issue.  Hope this helps. Cam.

[SupermotoFan]

Cam,

Thanks for all the good info.

With my current situation (worn out stock-size cylinder in need of a boring and replating, and not having the time or money to do the right thing right now) I'm going to put in a Wiseco (stock size) and putt around for the weekend (good friend's 40th celebration next to a big OHV park in California).

The guy at the shop recommended Motul 7t (Ester based full synthetic) at 32:1.  I'm thinking at least 40:1 with your comments about how oil burns hotter than fuel.

Once I get the cylinder cleaned up, and another new piston to fit the new bore properly, I'll follow your advice about seeing how thin I can run the oil.

Thanks again!

[Utah]

Good info here! I am just back on to dirt bikes after close to 5 years off. Will pick up a new for me KX250 ('04) tomorrow. So, as I read this sounds like smaller cc bikes may rev higher so higher ratio of oil to fuel is in order. Good quality synthetic oils w/ high "shear" value allows for leaner mix. Did I get this right?  W/ 250, am I safe to run say 80:1 for a mix of slow trail "bog" (when riding with GF) and flat out rip across the desert when I head out on my own? I'm thinking I'll probably run klotz or something similar.  Appreciate the input!

[martinfan30]

So from the guys running 100:1... Any issues as of yet? Or still running strong as I suspect?

[Mick]

But, as hard as I ran my KX, I did notice when I started running 32:1-40:1. It surged worse. Running 50:1-80:1 I noticed it wasn't so bad.

Not implying that you didn't already know this, but just for riders who may not understand what's happening:
Running a rich oil/fuel ratio (premix) LEANS out your jetting.  That's correct...it's like using a smaller pilot/main jet.  Without increasing the size of jets in your carburetor, transitioning to a 32:1 premix from a 50:1+ will cause surging typical of a lean running motor.  It has in fact become a lean running motor when you've about halfed the amount of fuel the motor is getting by increasing the oil ratio.  The opposite is true when you transition from 32:1 - 50:1+ the motor will run rich unless appropriate jetting changes are made.

I heard that even though Amsoil has a "full synthetic", it is not. I was told that it still has some form of bean oil in it. And that is the other thing...bean?

This is true, but it's not an issue to cause alarm.  Synthetic oils today are a combination of ester packages and formulas to meet a desired criteria/goal.  Amsoil has likely added some blend of esters formulated by Castor bean oil to augment their add package.  Doesn't mean it's castor oil, and it curtainly doesn't mean it's not synthetic.  Each of those claims would be totally false.  It just means Amsoil is takeing advantage of a particluar function of castor oil by including a very specific "ingredient" that performs similar to the compound from which it was created.

And now to throw my flavors in,
I run Torco GP-7 @ 50:1.  I'll likely switch to Amsoil Dominator after I finish off my Torco supply.  Although Maxima Super M looks good too.

[kaw rider]

40:1 is good for stock hp
32:1 is good for 75 hp
16:1-32:1 FOR +75 HP.

[martinfan30]

Didn't i read something in here about determining correct ratio by the amount of oil that pools in the bottom of the crankcase? I searched but no luck.

[hughes]

Some people try to run leaner fuel/oil ratio's to compensate for rich jetting conditions/black goo running out of the silencer etc. You always need to consider that the lower end of the engine needs proper lubrication just as the cylinder. I have always ran 32:1 with proper float heights some mild jetting changes and bikes have always ran clean with no plug fouling issues nor black goo running out of the silencers. I prefer to run Yamalube 2R @32:1. There's no benefit to running leaner fuel/oil ratio's other than making your quart of 2-stroke lasting longer.