Fuel flow issue. 1986 vfr 700f

FUEL PUMP DRAWS FUEL OUT OF FILTER BUT FUEL FROM TANK DOES NOT FLOW TO FILTER.
This has been going on for years and started on the way home after having bought the bike. I replaced the fuel pump but that was not the problem. I have cleaned the tank, replace the fuel filter many times, checked the fuel cap, petcock and fuel lines. If I turn off the petcock, removed the fuel line to the filter, turn the petcock back on, fuel flow readily from tank. I prime the filter, replace the fuel line and bike starts and runs well but it will happen again immediately or in a day or two. If anyone has thoughts and recommendations, I would like to hear from you.

 

Have you checked your tank vent lines? A blockage will cause sporadic fuel flow problems.

 

I have blown up the vent pipe and it appears to be clear. It seems to me to be a vacuum being created between the tank and fuel filter. Does the vent pipe vent from below the fuel cap as opposed to inside the tank ?

 

There should be 2 vents, one for beneath the fuel cap (for over fill spills), and another for the inside of the tank (so a vacuum isn't created as fuel is drained/used).

 

Will look into the one inside the tank and see if this is the problem. Could be a good catch on your part. Thank you.

 

Vent pipe clear I am afraid. Is there a vent in the fuel cap that could be blocked and causing the fuel flow problem ? There is only one vent pipe on this tank, which I believe is original, and it vents around the fuel cap for overflow. There is no other vent. I took off the petcock and it is clean and clear. Tank is clean with no dirt or rust in the fuel. Fuel strainer inside the tank looks OK from what I can see. The last possibility is that the fuel cap has a vent blockage if it is in fact vented ?

 

Bought a new fuel cap, petcock, OEM filter, fuel line from tank to filter. Will test once all parts have been delivered. Will this solve my problem ?

 

After the fuel tank restoring (following a crash) I had a problem: opening the fuel cap I note that vacuum is generated inside. I had a engine stop caused by the fuel lack.
I've dismounted the fuel tank and opened all accesses (cap, petcock, level) and inspected with a camera inside. The tank is clean and the two pipes are in correct position, I hope, The big one for over fill spill is opened and connects the fuel cap area with the fuel tank bottom, corresponding withe the rubber funnel on the moor. The smallest tube, reaching that latter position in the bottom, end inside the fuel tank, about 1 cm, in the front direction, from the noon fixing bolt. If I blow air in the small tube, from the bottom end, it is locked.
My questions are:
1 - do the small tube "breath" from the tank plenum?
2 - could be the locked tube the cause of the vacuum generation?

 

The tank on non California bikes from those years vented through the cap, California bikes had a sealed cap and vented through the emissions canister. If at some point the cap was replaced with a California version (can not tell them apart visually) it will cause this problem. Seen it a few times.