Hello everyone, im new here, and i want ask about carburetor size and jets sizes. I have Yamaha DT 50 MX 1991r. I have Airsal 70ccm cylinder, and Dellorto PHBG 21 carburetor, i buyed motorbike on that configuration, so i want ask that carburetor isnt too big for that cylinder, and also what you think what jets size i should use on it to get best performance, i read many topics and almost on everyone guys says 17,5mm carburetor are the best for 70ccm. Should i buy new carburetor ? Motorbike works, also i have unlocked cdi unit, but max speed what i get its about 55-60km/h. That speed are everythink what i can expect ?

PS. sorry if i my question are dumb but this is my first contact with motorbikes.

I think you are getting a good speed for a 50cc bike. In the UK a standard one would be expected to go to around 48KPH.

I don't know anything about the carb but you can judge that the bike is correctly jetted by looking at the spark plug.

Please remember to say hello in the new members section. People tend to get more, or better, answers to questioned when they do.

thanks i do, btw in this 21mm carburetor i have 85 main jet and i start thinking its too small, but im not sure. I have 70cc airsal so its should go faster than 60km/h i read here about some dt 50 go about 40-50 mph and its about 80 km/h .

My DT50 with a 60cc big bore kit used to do 50mph, iirc i was running the stock carb with a 98 main jet

My DT50 with a 60cc big bore kit used to do 50mph, iirc i was running the stock carb with a 98 main jet

you have only bigger bore kit or exhaust also are tuned?

my donkey was as tuned as i could get it.

bigone exhaust and expansion pipe, fibre reeds, big bore kit and was geared up with a taller front sprocket and smaller rear.

my donkey was as tuned as i could get it.

bigone exhaust and expansion pipe, fibre reeds, big bore kit and was geared up with a taller front sprocket and smaller rear.

what sprocket config you got? also what exhaust you have gianneli? maybe have some link to store when i get that one?

Im having same problem .ive a 88 jet but dont know my thread size so i can order jet for 60 cc kit