Join Date: Jan 2009
Location: South Central PA
The problem I find with using a 250 petcock on a 450 isn't so much a matter of vacuum vs not, but rather fuel flow. The 250 petcock is 3/16" diameter. not much fuel needed for a single carb. The 450 is 5/16", needing double the fuel flow to feed two carbs and a larger appetite.
Ther are people that have successfully converted the 450 petcock to a gravity fed by blocking off the vacuum diaphram (solid plate) and plugging the line from the head. IIRC, it was recommended to do an overhaul of the whole thing to make sure there were no restrictions. YMMV
Comments contained in my posts are not intended to cause physical or psychological stress and are mearly my two cents worth, and in this economy, that's cheap!
Midnight Venture - Black Lithium II...