Common fuel valve problem?

[McDog]

My tank is full but my ski won't run with the fuel selector in the "on" position. It runs on reserve, but still seems to act as if it's out of gas at times. I checked all my lines and they look fine. I guess I need to check for trash in the carbs but I think it has something to do with the fuel selector. Is this a common failure for the fuel selector valve?

 

[XtSuperJet]

just take the fuel selector out and blow in it to see if it's got any crap in it.

 

[Higgins-LCHC]

I had the same prob. I took the petcock valve out and cleaned both the on and res. fuel lines. I got a 2 1/2 inch long white worm looking chunk of crap out of the on line. I still have no idea what it was. Runs like a champ now.
Higs