Ragz,

Yes tygon can collapse.. I use 6mm clear so I can see whats happening.. You need to go thru the system again and make sure all the fittings and connections dont have a restriction... on my rookie, it did the same thing.. it ended up being the tank vent having some additional brass casting.. I drilled it out and problem went away.. I used to see the tanks and traps flex...

Troubleshooting>>

Take the main feed line from the air trap and push fuel backwards through it and flush the system into the header tank.. then pull the header and dump it and clean it.. check the fittings while there.. then put it all back together.. fill it normally, and pull the fuel through the trap with your fueling pump... you can use a smaller battery or lesser voltage but if it flows through the trap and tanks and the bungs with the fueling pump, it will work normally... i use my pump to check out my systems on every install before running it...

if you are pulling fuel thru your main line and watch the tanks to see if any of them are getting sucked down or sqeezed on the sides, watch for bubbles... on my elan, I got a piece of fiberglass out of the system.

when its all done.. put it all together and run the motor half to 2/3 and make a ground run and feed all the fuel out down to the header to make sure...shake it, watch for bubbles.. I dont like the soft tubing myself..