Question: This may be a ridiculous question, but I would like to know the correlation between air/fuel ratio and oil/fuel ratio rich/lean mixture. Is it acceptable to lean out the oil/fuel ratio from that of the manufactures recommendation to compensate for rich running conditions. I use Golden Spectro 2stroke oil in my ’99 KDX 200. Manufacturer recommends 32:1,I run the Golden Spectro at 40:1 and sometimes leaner and I find this to be acceptable by reading my spark plug. Please, could you inform me if I’m off track?
Answer: Its not a ridiculous question and you are right on track. Golden Spectro is ideal at 50:1 in the KDX 200 and the affect on fuel mixture is as follows: A change from 32:1 to 50:1 oil fuel mix = 1% in percentage of oil present. 50:1 = 2% oil and 32:1= 3% oil So, at 50:1 you are 1% richer on FUELfollow that? 1% less oil = 1% more fuel.
Mikuni jets are metered in percentage increments. So, a 170 main jet is 10% leaner than a 180 main jet. In order to compensate exactly for the oil ratio change, not accounting for air density, you would need to go leaner 1%. If you have a 180 main you would have to scrounge around for a 179 main jet. Good luck! They don’t make them.
More important though is what happens in the low and midrange because we can feel the bike running a little richer there when we go leaner on oil. Well, some of us can. So, the best course of action is to turn out the air screw a 1/4 or 1/2 turn to clean up the bottom to compensate for changing from 32:1 to 50:1. THAT’S ALL! (provided by Spectro)