Air cooled and Water cooled fuel mix

[TheDamo]

Is it possible to run two water cooled bikes 84 yz and 89 rm as well as an air cooled 76 yz on the same oil and fuel ratio successfully?

[Nathan S]

Yes. I've been running my X and my KX125 on the same fuel (96 octane, Motul 800 at 30:1) for years.

Assuming you're talking about fairly stock motors, How hard you rev them matters at least as much as air vs water cooling.

[Rossvickicampbell]

I agree with Nathan - run mine - regardless - on Silkolene at 40:1 - have had no issues?

[oldyzman]

agree with Nathan, i run Motul 800 30:1 with BP 98, in everything from old RM125A to modern KTM300. I only mix what i need and after 1 week the leftover goes in the missus car' s next full tank.

[80-85 husky]

ive run watercooled bikes happily at 100 to 1 but I wouldn't go over 50:1 on an aircooled bike. I use motorex full synthetic and have had no drama in the kato 300, the husky 400 and I use it also in the chainsaw and the blowervac. all good.

ive recently changed to the semi castor at40:1 just to get the smell!

[skypig]

Oil ratios are like: "What oil is best?"
100 people with 100 stories.

The general consensus seems to be that modern synthetic oils will keep your engine from premature wear at 60:1 or even leaner.

There does seem to be a ground swell of people that believe 25-30:1 actually offers an advantage in ring sealing and therefore power, especially in older design engines. I.E. Those that were designed to run at around 20:1.

Does Maxima Castor 927 still have the disadvantages of the old castor oil? (Gum/turn to jelly in the carb)

The number of oils available is over whelming. Motul make several full synthetic 2 stroke oils.

I use so little, I don't care what it costs, if it was actually "better".

I'm running the very first model of water cooled Suzuki 125. A 125X.

I used "Bardahl" back in the day, one of the first synthetic oils as far as I remember.

[80-85 husky]

Does Maxima Castor 927 still have the disadvantages of the old castor oil? (Gum/turn to jelly in the carb)

Christ I hope not....

[TheDamo]

Based on the replies so far it seems that a late model 2t synthetic like motul 800 will happily work at 40:1 in an older air cooled bike as well as a pre 90 water cooler.

[Nathan S]

If you ever get the X onto the mainjet, it will want more oil than 40:1...

Until then, 40:1 will be fine!

[Slakewell]

I do not use modern oils in air cooled bikes. Testing has shown me that they make the engine run hotter because they burn to well. The unburned oil actually helps transfer heat from the piston to the cylinder and out to the fins. Modern oils leave an air cap around the piston. Put a heat sensor in your header pipe and run different oils and see the difference. After seeing the results for myself, I now use old school mineral oil in air cooled bikes.

[skypig]

If you ever get the X onto the mainjet, it will want more oil than 40:1...

Until then, 40:1 will be fine!

Unless you get it on the mainjet, you won't get it out of the pits!
Nothing in the way of midrange!! Nothing.

Actually, I'm slowly getting the jetting and midrange (1000rpm below max, ha ha) slightly better.

At CD I was finally keeping it in the band long enough for the big jump.

I've been using Motul 510, at 25:1 (semi synthetic)

[Lozza]

I do not use modern oils in air cooled bikes. Testing has shown me that they make the engine run hotter because they burn to well. The unburned oil actually helps transfer heat from the piston to the cylinder and out to the fins. Modern oils leave an air cap around the piston. Put a heat sensor in your header pipe and run different oils and see the difference. After seeing the results for myself, I now use old school mineral oil in air cooled bikes.

"air cap around the piston"    ??

[Nathan S]

Skypig, YZ125X, not RM125X.
I sold my RM125D because my YZ125X was 500% better down low, 100% better in the midrange, and only gave up a bit in top end. (This post may include some exaggeration - but probably less than you think).

None of the above is meant to disagree with your post, BTW.

[skypig]

Skypig, YZ125X, not RM125X.
I sold my RM125D because my YZ125X was 500% better down low, 100% better in the midrange, and only gave up a bit in top end. (This post may include some exaggeration - but probably less than you think).

None of the above is meant to disagree with your post, BTW.

All good, I'm always smiling on this forum.
Interesting re your RM125D. Suzuki changed the motor from "case reed" on the X, to full reed on the Z and D for "more midrange". Imagine what the X is like!

Unsurprisingly, when I was a teenager moving up from a YZ80, the RM125X powerband was just fine.
Now I'm a slow old man accustomed to modern 4 strokes, its almost unridable.

I think there is still a small improvement to be had. I ran out of needle clip positions (each position richer was an improvement) and now I have the next richer needle jet in my box of tricks, which according to the experts will allow me to put the clip back in the middle.

All good fun.

[pokey]

everyone has a story on why their oil is better than yours and they have used it for years without a problem. thats lovely and good on them .

One of the best things that oil in an aircooled does beside make things a bit slippy is transfer heat away from the hot  bits. this is the wicking effect and some oils are better than others at it.

Yeah sure you can run the same mix but why would you if the engines were designed to run on different oils and mix? its not like you can just run down the shop and pick up a vintage piston and rings  if it nips up because you used a mix that wasnt good for it.