In Bill Silver's books on Honda 250/305's, he shows a Honda Service Bulletin that recommends drilling a second vent hole on the underside of the gas cap, 1/16 th inch dia. on the opposite side from the original vent hole on the underside of the rim just outside the gasket. (be careful to drill through the top of the gas cap). Even new replacement caps may only have 1 vent hold!! These gas caps can be dis-assembled to be cleaned and drilled by tapping on the outside edge of the upper part (exposed side) of the gas cap. Pay attention to how it comes apart; the cap is assembled by pressing the parts back together after cleaning and adding the second vent hole.
This may or may not correct fuel delivery problems to the carbs but it was what Honda recommended in the mid 60's.
This may or may not correct fuel delivery problems to the carbs but it was what Honda recommended in the mid 60's.
