HELP I Have Fill & Vent Issues on 1973 19.6 ??

[Dannys Dream]

Looking for input .... So I have 95% completed a restore on my 73  19.6 and seems to have come out very nice ,,, and when i had the deck plate off to inspect the fuel tank I was surprised that the tank had already been replaced with a what I believe is a TODD 35 gal poly. We stripped the fuel fill & vent lines and replace with OEM sized new. The poly tank has the Vent at the back (Stern) of the tank and the fill at the front end (Bowl). Problem is that the vent only seems to work when the tank is 1/2 empty and putting the last 10 gallons in is always a struggle as it wont take fuel. Then when I do get it to what I perceive is the topped off the pressure is so high I can barley get the gas cap off to check to make sure I'm good to go ?? The last 3-6 Gals may take 4 hours to get in like 1/2 to 3/4 gallon at a time. You can hear and feel the pressure relieving as I screw off the cap. This pressure in turn makes the engine (1983 110 Johnson) leak gas on hot days back thru the carbs. Not sure where to go short of taking it all apart again and replacing the tank   ??????????  Any input guys ?????

[Aaron43]

Can u tilt the tank by propping up the end with the vent on it?....then as u fill it the air will collect below the vent and easily escape as u fill it...Did u check the vent itself....I have seen bugs plug up the vents...

[RickK]

 
Check the vent line.
Oh and post some pics of your rebuild so we can celebrate with you .

[CLM65]

Make sure your vent has a continual slope up from the tank to the deck fitting.  Any low spots will make it act like a trap and prevent it from working properly.  Also, my Inca poly tank for my project boat came with the vent port plugged (for FME control).  It looks like it was molded this way, and it is not obvious unless you look closely at it.  Maybe whoever installed the tank forgot to remove the plug?

[RickK]

Wow, I guess I should check my Inca tank before I install it.  Thanks Craig.

[Dannys Dream]

Thanks for the input and I will try pulling up any slack to the vent Craig ... Like it said it spits when the tank is 1/2 empty. Anything more would require de rigging and I might as well replace the tank with a 50 while it's all apart.