Modern Vespa

Just had my px125e engine rebuilt after a seize. It has had the dr 177 piston and rings replaced and the crank has been changed to a mazzucheli crank, it also has a 21 tooth cosa clutch. For some reason it will not start without the airfilter on where as before it would. I am now running it in but just don't understand why it needs the filter on to start. Is it anything to do with the new crank?

may be very lean. Maybe the air filter restricts just enough air for it to start..?

is that a good thing or bad thing?

the spark plug colour is right but then I am running it in gently. Takes a lot of kicks to get it started in the morning. Never used to.

What jets are you running with the new kit?

they are the same as before, main is 116/160. It had the dr kit on it before but just had new piston and rings put in after the seize, but after striping and inspection the head was nothing to do with the seize. Was wondering if the new mazy crank that's just been fitted would have anything to do air filter. The guy that did it for me tried 4 different carbs and had to put his finger over the idle jet on all or the air filter back on to start it. Conks out if loosened or taken off. At work at the moment but will let you know what the idle jet is later. Thanks

p.s ran fine before and also had the heart shape holes drilled out of the filter without any problems. The timing is on IT

p200 carb