70cc's For The Honda Express

New piston 46mm bore vs Old piston 40mm bore

New piston see the intake Port on the top side

Big Bore install complete, Look at those fins stick out past the head, new size 65cc's ,thats a 33% increase, present speed 43mph that's a 30% increase
I installed the big bore kit and adjusted the carb air mix more rich ( left/counter clockwise)
I also adjusted the oil pump for maximum I am also adding a mall amount of oil to the gas ( just to be safe)
There was some lean surging when cold untill I move the throttle needle to the bottom notch and adjusted the carb again ( I have re-jeted the carb to a #81 jet since then)
the NC/NA 50's with wind up starter (77 - 80 ) , DO NOT have an adjustable oil pump it will be nesscessary to use premix fuel if you go big bore mix at 24:1

70cc kit by mfg by DR Racing and Purchased from www.50cc.nl , contains, new aluminum piston , new 46mm bore cylinder, gasket kit

I'm using a 1977 express carb & intake and mounted a 2pc Biturbo exhaust designed for the Tomos moped ( a cut & weld mod is nesscessary to attach the biturbo to the express exhuast pipe ) ,the biturbo came Themopedwarehouse
the head HAS to have the chamber opened up so it is the same diameter as the new bore try to mantain the same contour , and a new drive belt has been fitted, the variator has had two of the rollars/weights removed.

A bolt on ( NO welding ) Proma performace style exhaust is available from VT cycles in Hawaii for $55 plus shipping. He informs me these are of limited supply.