Originally Posted by
rspears
Contraction is not your problem, as it's sucking air into the tank to replace fuel burned, or due to decreasing vapor pressure due to cooling. Expansion (or a leak) is what causes the fumes. That vent has to work both ways, so a check valve may seem to fix your problem but is going to pressurize your tank with increasing vapor pressures, especially in the summer. Dave (IC2) already shared his experience in your earlier post, including the fact that the charcoal canister doesn't work for a vented system, and his solution, which was a coil of tubing in the vent routing. Seems to me you have the answer, or at least one that worked for Dave.