CR125 Fuel:Oil Mixture

2 Stroke Kart Engine Forums
1

I bought a used Swedetech built CR125 kart. After reading a ton about fuel, I settled with Sunoco 110 Leaded Race Gas (I wish the airport would let me buy 100LL, would be much closer).

I also adopted a jetting chart, which was made with VP98 Fuel and 24:1 mixture.

I don’t plan to race. So I don’t mind going oil heavy (and I guess leaner).

Now, Swedetech (and Honda) recommends 32:1 mixture. Swedetech specifically says Maxima 927 Castor (which I do have). I also have Red Line Synthetic Racing Oil as well.

So if I go 32:1 with Castor, and add some Redline, resulting in somewhere between 24 and 32:1…is my jet chart valid anymore? Should I do another chart for 32:1?

Would it even be valid for 24:1 with 110 Octane (I would think so at Octane is anti-knock)?

Is 24:1 right for CR125? It sounds like a lot of oil.

2

24:1 is not uncommon for 125’s in a Karting application. They see a lot more sustained high RPM. 100cc non gearbox sometimes can be as much as 16:1 or 14:1

I think I’d be very cautious about the jetting chart when you have that many variables that were (probably) not accounted for in it.

I’m a little concerned VP98 might be a touch on the lower octane side of the engine is built to a high level. Typically folks would run C12 in those.

Long story short, I’d run 24:1 because why not. More oil won’t hurt unless you don’t jet to compensate and oiling up plugs shouldn’t be a problem. Start with a big jet and work your way down if you need to.

You’ll get lots of opinions and as long as people understand what you are running, any of them should be fine.

Lastly, I think I’d stick with one oil vs mixing two of them. Some people do it, but again I think keeping variables to a minimum will keep the fun factor up for you.

3

In my cr I used c12 and motul 800 @32:1 and never had an issue in the 40 hours i put on the bottom end. That was a mix of racing and practice days. More oil can’t hurt unless with fouling as mentioned above, if your just lapping, jet a bit conservative, put a little extra oil and enjoy

4

Thank you gents. I think 110 + Castor at 24:1 is it. That way I don’t violate anyone’s advice (including you, gents).

5

I made a computer program that figures out the needed ratio dependent on type cylinder cooling and max RPM and it says Castor 927 is good at 23:1 at 14,000 RPM. More RPM, more oil, and vice reversa.