my newly aquired 100cc 2 stroke quad starts and runs fine at low speed and load, the electric choke is working fine and it has had a complete new carb and plug....the problem i have is the same as before i had a new carb and plug, any ideas please.....

when applying throttle over say 25% it doesnt pick up revs, you just get an increase in smoke out the back! interestingly i tried restricting the carb inlet with my hand and it revs up ok? so, i can only assume that it MUST have the airbox installed, does that sound right? only problem is I dont have an airbox, will have to find the correct one and buy one!

 

I wouldnt run it too long like that, could be you are running super lean like that, the oil injector doesn't know how much fuel is going in, so you get more oil and less fuel, so it smokes more. Does the smoke decrease when you choke off the carb, increasing the fuel ratio going into the motor? that would definately point to needing the restriction provided by an air box. Or....you could go up about 2-3 sizes on your main jet and see if it runs like that, if you dont want an air box. Did you buy it without an airbox, or was the original one damaged?

 

I bought it with no airbox, so i dont have one. I have ordered one now, so will see if its the problem, just seems a bit strange, i have never come across an engine that starts and runs easily but wont rev up just becasue there is no airbox on, first time for everything guess.

On another note, how does the oil injector pump know how much oil to put in, is it just based on the engine speed?

 

On a snowmobile, the oil pump has an arm on it that moves as the throttle moves, increasing oil output to the carbs. Most ATVs have a small gear drive that runs an oil pump, it is set to deliver a set ratio at every rpm, so spinning it faster (revving motor) gives you more oil, if you are very lean, that would mean your mix would be a lot richer than it would with the correct air/fule ratio. Depending on the intake size of the airbox, it can make a huge difference to not have the box attached, especially for a 2 stroke motor.