Another starting problem!

[Scootie32]

My sons scooter has run fine for 12 months. About a month ago he put his engine in his other scooter that has just been repainted. On its first long run it pulled some dislodged dirt through. So tank and carb were cleaned out. We went to Newark last weekend and he used a load more fuel than me, same engine set up, fuel spitting back through the carb like you would not believe! Anyway we found out the float has developed a pin hole and filled with fuel. New float and clean again. The out come is it will only start with a squirt of fuel down the bell mouth then fine. So tonight swapped my carb on still the same, mine starts with his carb his still needs squirt with my carb fitted! Any ideas? I was thinking May be damaged rings? So not enough suction to draw fuel through when kicking? Both scooters are stage 4 tuned 200's with 30mm Dellorto carbs, Rayspeed electronic ignition with lightened flywheels. I was thinking we had better strip the engine and check the piston and rings this weekend.
Any help much appreciated, Andy.