PX 150 Four Stroking on Cold Start

Hi folks,


I have a 2014 PX 125 fitted with a Piaggio 150 Cylinder & Sip 2.0.

20/20 Dellorto

100 MJ

145/160 IJ

AC 150


Drilled Airfilter.


My problem is it four strokes from a cold start with the choke. I pull the choke and start it and it turns over after about 6 turns then I kick the choke in and rev up. When I ride off it four strokes for around 3 minutes then runs perfectly from idle to WOT. Once warmed up it starts on first turn when I press starter.

On inspection the choke mechanism returns to fully closed inside the carb when kicked back in and is not sticking....

I tried a leaner IJ - 42/160 but it made no difference. 

I set the mix screw at 2 turns then found best running at 1/8 turn in as it would bog down if turned in any direction either way.

What could cause the four stroking ?

Many thanks,