Just finished building a 62 Series 3 150cc and stuck a 175 piston and barrel on.
So started it up and it just would not tick over...
Tried the usual, air mix screw/ throttle tick over screw -Checked Choke was working correctly.
Got it kind of ticking over once warm and then al of sudden it really over revved.... to the point I thought it might go bang, hit the off switch -did not work, pulled the HT lead off and it still ran as I walked around the scooter...and eventually blocked the air intake...a crazy few minutes.
Anyway I'm guessing I have a massive air leak so will do the inner tube test over the manifold inlet and exhaust, soapy water.
I noted some carbon/ soot on the exhaust joint once engine had stopped.
What pressure do you typically put into the system to check?
Last question -Should I stick a bigger main jet in?? I had a look at the current one and think it was "108" -the original dell 'Orto carb.
Cheers
JD