Strange carb problem? Any suggestions?

[psgnw]

This applies to my PK 50 XL2 with a Pollini 75cc.



My old carb cracked at the manifold end. Ordered a replacement carb. Exact same type (Dellorto 16.15F for Vespa PK 50 XL2, choke rocker and everything). After fitting this carb and jetting it with the same jets (new jets of the same size, original Dellorto jets), the scooter boggs and four strokes at WOT. It also 4 strokes when i pull the choke when driving (as it should?).

The thing is the plug looks like it's running lean. After a 30km ride the plug is still more grey than caramel.



It does not have hanging revs (it returns to idle after a couple of seconds). It feels boggy and the throttle response is kind of sluggish.

I'm running with the recommended spark plug for ths kit NKG B9ES (as suggested by Pollini in the manual).



Spraying carb cleaner on the manifold does not change the revs unless it gets into the airfilter, then it slows down.



I have replaced the exhaust elbow that connects to the cylinder with a SIP performance one. Fitted with new gaskets and also some Dirko HT sealant on the outside where the pipe meets the manifold.



Shouldn't a air leak give me different symptoms? My limited experience would say it's jetted a bit rich, but plug says otherwise.



Any suggestions on how to solve this?

[jeanshorts]

Make sure the choke plunger is actually seating well.

[psgnw]

Worth a check

[oldscooterbloke]

have you checked the float level and needle valve works , worth a check

[psgnw]

Aha! Not checked. Just presumed it was all good since I bought a brand new carb.

[psgnw]

Riding it earlier today it was bogging horribly and fourstroked constantly. Would not go over 50 km/h. This was after I have gone over the carb manifold connection, so I think there where a tiny air leak there. Plug was pitch black.

Came home and reduced the main jet 2 numbers. Now it's almost back to the way it where before. Still missing 5 km/h from my old top speed, but it is responsive and only four strokes when going down hill. Did a 15 km drive around town and on some faster roads. A mix of town driving and WOT. Plug (brand new from the box before the ride) looks pale brown/slight tan.