excess gas pressure @ roll over valve

[smokin54]

1069558

'89,YJ,Carb,4.2,mech.fuel pump.
On any bumpy road, it builds too much presssure in the fuel tank and sprays gas all over the 1/4 pannel,tire, springs etc. from the roll over valve. I've replaced the roll over valve, rubber housing, & gas cap., checked all lines from motor and charcol canister. NOTHING seems to help.
ANY HELP PLEASE, I'M AFRAID IT'S GOING TO BLOW UP BEFORE I CAN FIGURE IT OUT!
P.S. It also sprays gas all over the muffler. :-? :-? :-? [addsig]

 

[Snitty]

1069588

do you have a vented gas cap? you should have a vent line on the tank to relieve that... it might be missing/plugged[addsig]

 

[jprtroy]

1069691

The fuel system is a close loop system, with a supply to the carb, and a return back to the fuel tank. The pump supplies fuel (under small pressure) to the carb inlet, the remaining unused fuel is returned to the tank.
Your tank will have a vent line, you need to inspect it for any kinks.
[addsig]