[motorhead11345]

hello, I have a 2021 cforce 500. today while out riding i stopped along the trail for a break, when i turned back on i noticed the fuel pump sounded funny while priming, when i opened the fuel cap what i thought to be a large amount of pressure was released, so i did some tinkering, long story short, the fuel tank builds pressure within seconds of placing the cap back on and the pump doesn't sound like it likes the pressure, but the pump sounds normal with the pressure released. my question is, is should it be building pressure that quick? i did check the pressure release on the cap and its moving freely and passing air when pressed...... I just dont like the rapid fuel tank pressure build, and the sound of the pump. any help or info is appreciated. thanks.... p.s. the outside temp was in the upper 80s F

[NMKawierider]

Some pressure on the tank is normal as it is actually minor. Vacuum is not and is a symptom on a bad check valve. Getting back to pressure and especially quickly produced pressure, this is s symptom of excess engine or exhaust heat not being shielded from the fuel tank which causes more rapid expansion..even boiling of the fuel to create excessive pressure. This boiling can also put bubbles in the fuel which the pump picks up and makes notable changes in noise ..and adds this vapor to the pressurized side of the system. Fuel lines in this area also are susceptible to this heat and vapor-locking can occur when the fuel in the lines becomes vapor. Heat is the problem.  So...check for missing heat shielding. Add some on the lower side of the tank if you can. Of course moving faster also moves more air through the chassis which also move heat out so...go faster!..and no stopping and idling it.. lol