Hello! guys, I need a little carburetor and tuning lesson on my rotax max. It has done well, at least 10 rides, but I would like to make some adjustments to optimize performance. I find that it stalls a little at low rpm and I thought I would try lowering the main jet to a 162 and maybe 160, since I have a 165. I changed my gear to 12, since I had a 13 and see the difference, the sprocket is an 82, and I reach about 12500 rpm max, but the guys have 84 - 11. I tend to find that it revs quite fast and don’t want to wear it out for nothing, just to have better recovery. I have read a little about it and I know that you can play with the needle in the carb, the main jet, the air/fuel screw, but I don’t really know. My needle is at the second position, jet 165, air/fuel screw at 2 turns, spark plugs br10eg, which I will perhaps change for a br10eix, and my mix is 2.25%. Merci !
I will take all the advice that will be good for me, what is best to do and how all these settings work and how to test them without breaking.
The difference in gearing is pretty significant and is going to cause low end problems. Run the same gearing as others so you can run it in the RPM range it’s designed for. As long as you are up on maintenance, don’t worry about wear. If you’re not sure on how the engine has been maintained then that is the next thing to do.
Adjust the gearing first, then adjust other things as/if needed. The EG plug is fine. I can’t stress enough how important gearing is. Next look at power valve if low end performance is still slow AND your apex speeds are similar to others, then dig into other changes.
Agree with James - throw the 11 tooth driver on it and let the motor rev some more.
The Max is a very reliable motor - as long as you’re running 2-3% oil in the fuel, have water in the rad, gradually bring the motor up to temp on COLD days, and aren’t leaned right out (the engine will “pop” when you go too lean), they’ll last for 50+ hours before they need service, if all you’re doing is playing.
When you’re that far off on gearing, you’ll never really be able to tell where your carburetion is at.
What minimum RPM do you see at the slowest turn? It should not be any lower than 7000 RPM. Best would be better if it’s 7500 RPM. If you’re coming out at 8000 RPM might indicate that your gearing is too short (too many teeth on the axle) but it depends. Like what James said if the RPM is too low, carb adjustments won’t add low end torque.
How long is the track? Typically, short tracks use shorter gearing and longer use tall gearing but not always but it depends.
Not sure if you are racing but if you are, then you need to run whatever makes you fast and not worry about wearing out the engine. If you not racing, then sure run a taller gear.
Rotax motors typically like to run taller gearing. Also, when you add throttle, it needs to be applied gradually, sort of roll on the throttle but don’t mash the throttle. When I raced Rotax, I sort of lead the throttle position as the RPM increased.
Perfect, thanks James
I’ll do what you say and start with the gearing and then adjust the rest if needed. Very good advice!
Perfect! Thanks Rob
You are quite right.
Thanks Larry
I’ll check all this out, it’s very enlightening and I’ll come back if necessary.