Malossi "Sport kit" for 2002 Vespa ET4 50cc

Hi, need some help.

I am rebuilding my ET4 and have bought the Malossi "Sport kit" from SIP. Variomatic, clutch an so on.

I first changed all the old parts with the new ones from malossi, and immediately after startup the scooter felt heavy, underpowered and slow. It accelerated very slowly and only reached 30km/h top speed. To troubleshoot I tried putting all the old parts in again, and everything worked fine. Then I started to test each part: Just the clutch spring. Old clutch spring on new clutch. Old rollers in new variomatic. New rollers in old variomatic. No matter what I tried, just installing one of the parts from the malossi kit made the scooter slower and underpowered. I have checked and checked again that everything is properly installed, but nothing helps. I only get ok performance when using the original parts. Does anyone know of a solution?

 

PS. I have removed the restriction ring from the variator, the new malossi belt from the kit works fine. The included malossi air filter does not fit my scooter, I think it is for the 125cc.