TOPIC:

Last summer I had a several different gas issues with my small boats outboard. The 1st 2 were bad gas.(water mixed in) Finally came the conclusion that the cap must be bad and when it rains I get water in my tank. So after talking with a number of people I just went & purchased a new tank. So the first time out things were fine, all ran well. The next time out it was a warm day & as the day went on I noticed the new tank seemed to be swelling. (see picture) You'll see the old tank on the right and the new on the left. The new one had already had the pressure relieved but retained the some of the size.
I really didn't know what was going on & was starting to worry that the tank was going to split wide open. At first I didn't notice any issue with the motor but shortly after seeing the tank swollen the motor died on me. I smelled gas & the motor seemed flooded. Well to make a long story shorter. I ended up with the motor at Cabela's for repair. They told my the the float in the carb was stuck and that's what was causing the flooding issue. So after the repair away I went. The next time out it was even hotter and the tank looked like a beach ball. I called the trip early & a good thing it was because on the way to the ramp I had the same issue of flooding. By now I'm nuts with this issue. So I went home and changed the tank back to the old 1 with the old cap. After cleaning the plugs and starting it up I had NO issue. I ended up with the new tank but using the old cap.
I'm just wondering if the swollen tank added pressure to the fuel and then was pushing through the carb and flooding out my motor. Being that swollen it had to pressurize the tank. I did notice that when connecting & disconnecting the fuel line I seemed to get more of a leak. That's the only answer I could come up with.
Has anyone else had this type of issue or am I the only one? I just don't understand the idea of the new cap. Does it just keep swelling? I'm hoping someone else has had an issue like this so I'm not wondering if I'm crazy or not.

I can't say that I have had a similar issue but I have vents on all of my tanks. As a liquid heats it expands, contracts when cooled yes and will cause pressure or vacuum is there is not a vent. Pressurizing your tank can cause fuel flow to increase to you carb and a vacuum will cause your carb to become starved. Sticking floats are way too common with the crap gas these companies are producing. Setting in your carb for even a short period of time can cause small jets and floats to gum up and harden like glue. I have heard of some caps being designed with internal vents and even the portable ventless can to prevent something deemed important by the EPA. Mostly I have found it to be the start of inferior product production and I am hanging on to my older tanks and cans as long as possible. I also have started using products to help try to stablize and clean to combat the crap gas as I am using my smaller engines such as outboards, weed trimmers, ice auger, lawn tractor, etc.

I use marine sta bil in all of my engines marine or lawn mower. It helps with the alcohol in the gas and keeps the fuel fresher. No vent on the tank is the problem.