Correct fuel/oil mix?

[Dietrich]

Maybe one of you veterans can help me out here. I have a 1945 CZ 125 motorcycle. Great shape, all original and runs well. But smokes too much. I am not sure of the correct fuel mixture for this two stroke. Right now I have it at about 25 to 1. I will experiment but it would be good to know the right mix. Let me know if you can enlighten me.

 

Thanks in advance.

[Paul Mihalka]

In those years 25 to 1 was the common measure - I remember. Today the common number is 50 to 1. I don't know if it is due to better modern oils or better motor design and materials.

[Boffin]

My 1970 CZ was 32:1 and smoked like Victorian chimney. My later MZ had a variable delivery pump that went from 25:1 at full throttle to 50:1 at part-throttle.

 

Modern oils are better and if you do not ride at max-revs then less oil is needed.

 

Andy

[racer7]

I always liked my 2 smokers but CZs were well up the curve of smog production even in the day. You can reduce it with newer oils and mixing less- doubt you'll get rid of it. I even like the smell so you can run it by my place any time, no matter how much smoke you're making...

[Guest Kakugo]

All modern oil manufacturers recommend never to exceed 4% premix (25:1) while using both synthetic and mineral based oil.

However: I was advised by a Motul tech to try running even older engines on lower oil content premix. An engine which back in the '50s had to be run on 4% premix can now be safely run 3%. Modern oils, be them synthetic or mineral based are much more advanced of those available even twenty years ago.

I also run an old Echo chainsaw (recommended 4%) on 2% premix without any ill effect for a few years. I gave the chainsaw away three years ago and it was still going strong. Foolish thing as I now need a new one (the one I kept just broke down) and a similar quality item is big money...

[Rinkydink]

Smoke, within reason is good...be vewy vewy careful.

[UberXY]

On the advice from a jet ski mechanic, I have been using Amsoils 100:1 2-stroke oil for the last five years in my Yamaha jet ski (150HP), my 1990'ish Johnson outboard (90HP), and my Yamaha DT250 (19HP). I disconnected the oil mixing systems and premix all of them.

 

[Please note I am not an Amsoil evangelist; this is the only product of theirs I have ever used.]

[steveknapp]

My understanding is ratio is determined by the oil quality. But the oil quantity can impact the A/F ratio if you premix and change a good bit. I wouldn't mix a modern 2 stroke oil that "thick".

 

I've also had good luck with Amsoil 2-stroke oils. Usually Interceptor for me blended 50:1.

 

In my snowmobile I run the BRP suggested oil. It works well, burns clean, and is reasonably priced. It has oil injection that goes straight to the crank bearings from what I can tell, rather than mixing oil/gas.

[kmac]

A tip I would say is to take off the exhaust and soak it in some sort of solvent and get it as clean as possible. This is often a cause of excessive smoking. The old oils were all 25:1 or worse and smoked very heavily and that builds up and sits in the exhaust. Even when you go to a better and more modern 2t oil it will still smoke since it will almost never get it all out of there.

 

I run Maxima Super M. I have had great life on all of my race bikes. I run it at 40:1.

 

I am NOT a fan of Amzoil and especially NOT at the 100:1 mix. I can not tell you how many Banshees I have rebuilt and MX bikes that guys thought it was the hot ticket. I have never had an oil related engine failure with my Maxima.

 

If it does not smoke at all...shut it down.

 

As far as premix or oil injector. I am a fan of premix. That way I am SURE it has oil. I do a nice left and right slosh before each start to make sure it stays mixed and I ride with confidence. Oil injectors, especially on a 50+ year old bike are VERY prone to failures.

 

I doubt you have a oil injector on a 1945 though sine they did not get popular until the 1960s.

[outpost22]

On the advice from a jet ski mechanic, I have been using Amsoils 100:1 2-stroke oil for the last five years in my Yamaha jet ski (150HP), my 1990'ish Johnson outboard (90HP), and my Yamaha DT250 (19HP). I disconnected the oil mixing systems and premix all of them.

 

[Please note I am not an Amsoil evangelist; this is the only product of theirs I have ever used.]

 

All but one of your engines is water cooled and the Yammy is low output. I'd be more careful on an air cooled motor running 100:1 that produces decent H.P.

[steveknapp]

" especially NOT at the 100:1 mix" - The only oil they suggest for that is Saber, and that is recommended for lawn equipment.

 

I've never seen Amsoil recommend Saber, nor any of their other oils, 100:1 for powersports.