Fixing a gas cap to vent properly

[hamjet]

My old gas cap always vented well since new, but the rubber seal went bad, so I went to Napa to get a new one. I could suck through it just like the old one so I thought all was well, even though it looked like a different cap.. WoW!! Big back pressure when I tried to remove it a day later. I didn't like that so I thought about seeing what I could do. Looking at the bottom you can see the difference. so by spreading the small tangs, the plastic part comes right out. then with a small screw driver I pried the plastic ring off showing 2 springs. the small one lets air to enter the tank, the larger one lets built up pressure to escape, which wasn't to my liking. By cutting the large spring down and snapping the plastic ring back on, I could now blow through the back which means it won't build up as much pressure at the cap. But still not to my liking, so I snipped a little more of the spring, snapped it back together and now all is right with the universe.. It still gives a little puff when cap removed but nothing like before. I hope this helps those with too much back pressure, it work for me....