When I bought my kart from the previous owner he gave me almost a full 5 gallons of fuel that was already mixed for the rotax. I used quite a bit of it my first day at the track, but what I’ve got left isn’t enough for my next trip out. So, it’s time to mix more fuel. I filled up my tank over the weekend and I’ve still got ~1gal of the original fuel mix remaining. I have no idea what what ratio of oil/fuel was mixed previously and with what brand of oil.
I bought some Motul oil for rotax and going to mix up a new batch of 5gal in the next day or two. I’m looking to drive this weekend. So my question is: how much of a risk do I take when mixing two fuel blends for a very short period of time? Am I supposed to purge the whole fuel system somehow first before I start using my own fuel mix to avoid some kind of problem(s)?
To be safe, drain out what you have in the tank and replace with your new mixture. What you drain out will run in your lawn mower. More than likely the different oils will mix properly, but I wouldn’t tell you to do that. What will be affected is the jetting if the two fuels have different gas and oil ratios. If you add your new mixture to the remaining fuel and then pour that mixture into a partially filled tank, the oil/gas ratio is going to be constantly changing. It’s not going to be a large change, but still a change. You’ll want to keep your jetting changes based on just the temperature and barometric changes during the day.
LAD Specialties customer / tony kart / rotax / kt100
Finish the old fuel first, or wait till you can top the tank off
And then start with a new batch at 60z per gallon (it is ok to mix 1/4 to 1/2 a tank) if anything it will run better. Considering the fact that you’ve already ran the engine on this fuel with no issues?
You can always mix new fuel in the tank with new fuel from your jug
But I highly recommend that you mix your 5 gallons of new fuel first
If lack of containers is an issue, then keep the old fuel in a lawn equipment container, that way your 5 gallon jug is empty and free from old fuel mixture
You could always use the rest for your weed eater or blower.
If I understood your question correctly, then this would be my answer.
I always ran 4oz per gallon on a Rotax although I think the manual even recommends less.
You shouldn’t mix different synthetic oils with each other but you can mix castor with synthetic. The thing is you don’t know what is in the other fuel so don’t mix anything with it if it’s going to sit over night. Use the old stuff until your tank gets low then use the new stuff. You don’t have to purge your system or do anything special except check your jetting as mentioned above.
Keep one bottle marked “premix only” that way three weeks from now when you’re scratching your head wondering if there’s oil in that (clear looking) gas, you’ll know for sure by the bottle it’s in.
FAA certified jet engine and aircraft technician,
Nicholson Speedway class champion 2001,
Yamaha KT100 Service Center,
41 years karting experience