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There is a current thread going on the 701 forum dealing with what you're talking about. I agree it does sound like it may be a problem.
My Pegastol wings have a single 30 litre tank in each wing. I feed both tanks to a 15 litre header tank behind the fire wall which in turn feeds the engine.
I put a sight glass (clear plastic tube) on the header tank to ensure there is sufficient fuel available/visible. Haven't had any problems with fuel flow from the wing tanks to date. I think from memory the tanks were originally intended to be vented at the wing tips but I have put an ali tube vent on the top of the wing facing the airflow. The theory being that it pressurises the tanks slightly. Seems to work.
I've got both tanks out at the moment to try and sort out a few leaks and was looking at putting an outlet at the rear of the tanks as an extra. At the moment there is about 4.5 litres unusable per tank.
Happy to help with any other issues you might have.
if you have a 701 # you can access the 701 forum on this site.
here's the thread, I don't know if you can access or not.
read all the way thru
so your outlet is on the same end as the filler spout? Something's not right about that. Can you post a pic of it?
That sounds like a tank designed for some level ground type operation. Feeding from the front won't work unless I missed something big in fooling with these things for 50 years. The inlet needs to be front outboard top and the outlet near the rear corner inboard bottom.
I'm not that familiar with the 701 wing tanks, but from the fuel tank drawing at CH701 Sample Drawing 7-V-11.pdf it looks like the fuel outlet is at the aft bottom corner of the tank.
Please ignore my post above. Reviewing the available literature on the 701 Pegastol wings, the fuel tanks are very different. My apologies.