Scooterotica

I have a problem, my vespa polini 231 runs great except it will not tick over, is extremely rich on tick over and hard to kick start. The tick over screw has no effect and is all the way in, I have gone from a 55 to a 48 pilot and it helped a little but runs to lean to keep it like that. Am I right in thinking that changing the slide may help this problem? It has a 4.5 standard slide in it, as a new slide is £50 I would like to only have to get one, so do I get 5.5, 6, 6.5,7. Is it just trial and error? I know that the higher the number the leaner the slide will be. I know each point difference in the slide equates to 1mm and was thinking of a 6.
My set up is a polini 221, 62mm crank, RD reed on a Taffspeed block.
Thanks
John

I had the same issue with my airstriker 35. After messing around with it for a while changing slides and even cutting the cut away bigger in the weakest slide I drilled out the pilot circuit hole which worked

cut the tickover spring in half with a pair of side cutters and try again,let us know how you get on

Thanks guys for the replies, will try cutting the spring first.