Mine shot up to 60 after installing a 340 Walbro. Couldn't turn it down. Had a case of of the Saginaw fitting blues. Hadn't heard of one shooting up with a 255 but anything is possible. That first pic that brad posted showing where to cut the little vent window may be your solution or drilling out the Saginaw fitting to allow an increased volume of fuel to return to the tank. Have you tried just adjusting the regulator to lower the pressure?