Thank you guys for your inputs.

I will first test it again after the mods i did in [link=http://www.rcuniverse.com/forum/fb.asp?m=9373056]post 73[/link].

If still not OK, I'll do the flow test as you described, Oliver and have a closer look at the inside of the PST trap.
I have a few of those brass porous pickup clunks in diferent sizes lying around, so I could replace it my self if there looks to be something wrong with it.

Will report back after I've run it again.

Happy new year guys!