Q: Dirtbike 2stroke can't reach high rpm

asked by on August 06, 2017

I own a Kawasaki KX85 Dirtbike (2 stroke 2006 model). Didn't start it for about a year because i didn't have time to change the piston. Now i've done and my first ride was amazing. That lasted for like 200-300 meters. Then it started to not being able to reach the high rpm on the gears. It gets to a point below the high rpm and loses all the rpm for about 0.2 sec and then picks it up again at the same point, like if i was pulling the throttle up and down but i have it at max. Later realized i mixed fuel wrong and had about double the amount of oil. Got the fuel right but no change after running a few small tanks. Then i realised i didn't have any oil in it (yes i have no idea how i forgot these things) then filled up oil and it went fine for about 200m again, then same problem. I should also mention that it goes a little better when running out of gas. And at low rpm it sounds kind of "blob blob" but picks up at higher rpm, and the blob isnt there when low on gas. I beg please help!

Hi There, It sounds like you may have a rich oil/fuel condition causing the motor to bog down or potentially foul out the spark plug. As you know, 2 stroke motors require a mixture of fuel and oil to keep the motor cool and to run properly. When there is too much oil in the fuel mixture, this causes the motor to struggle to burn the fuel charge as it enters the combustion chamber resulting in the motor bogging down as you describe. I would suggest checking the spark plug to be sure it is clean and not fouled with oil and fuel. If it is substantially black, you will want to replace it with a new spark plug. You will also want to be sure that the fuel/oil mixture is as precise as possible as this will ensure that the motor fires properly and is not too lean and not too rich. The reason it seems to run better when running out of fuel is the motor is leaning out and running on nearly all fuel and no oil for a few seconds as the motor runs out of fuel.

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