0.156" diameter orifice = an area of 0.019 in sq.
0.25" diameter line = an area of 0.049 in. sq.
You're certainly right that a 0.25" orifice is way larger than the 0.156". There is certainly no harm in using a fuel valve with this larger orifice (as some have done).
BonS - I don't understand your response "...the fuel line is 60% larger than a 1/4" ID hose and 100% larger than a 5/16" ID."
Yeah, that's not a very clear, or perhaps well thought out comment. I was trying to say to the OP that the fuel line is considerably bigger than the orifice in any case. I used the same OEM inlet and outlet fuel line diameter with my model 111 install.
I'd love to hear if a heavily loaded Valk (say with a sidecar, rider, wife, canine, tools, and a weeks worth of gear), doing 70 over the Grapevine in CA in July getting 20MPG would have any fuel starvation issues. Maybe, maybe not - I'll let you know in July.
I've been running the Model 111 for many years. I've never had any issue whatsoever unless I had a fuel filter or kinked fuel line. Last Summer, I ran my Interstate two-up with a trailer, into a very strong Kansas headwind and crosswind, on a very hot day, at around 80 mph. I got around 22-24 mpg, as I recall, and never had any fuel flow issues.
But I am pretty sure than if you made the entire fuel line 0.156" you may have issues at higher rpm's draining fuel from the float bowls faster that it could gravity fill.
You certainly may. There is even a difference between a thin and thick orifice plates with the same diameter hole let alone a long length of fuel line of that diameter. It has to do with the drag of the fuel along the side walls of the hose. Technically, the flow velocity at the wall is zero due to frictional drag.
