88 T2 weird fuel issue

[TehMonkay]

so i just got my 88 t2, with a full tank of gas, it lacks power, with 3/8ths or less, it cuts out randomly, between 3/8ths and 3/4 it hammers pretty hard, this is very strange lol. I am getting a walbro and changing the filter soon, there isn't anything else i can think of that would affect this like that unless perhaps there is some sort of check valve on the fuel tank vent that could affect it.