There is a real advantage in the three ports close to intake runners on the tri-power type setups to even fuel distribution. Especially with bigger carbs, the center vs end cyl's get a different fuel mix, I'd like to see an analysis of A/F ratios on different cylinders with big center-mount vs tri-carbs.
As
CZLN6 illustrated, the OFFY specific linkage is what I would call
infinitely variable. Designed ingeniously with simple rods and slip stops, the Offy linkage can be adjusted from
fully synchronous, to
variable progressive with two simple adjustments with a screwdriver. Depending on adjustment the
progressive linkage can open outer carb throttle plates gradually from just above idle, be set to snap to WOT at a pre-determined position on the center (main) or can open some throttle position in between .
On the '61/250 with a
tri-port Offy adaptor I've experimented with many multiple and single carb setups both synchronous and progressive. With a large 2bbl center carb, the outers can open progressively later into throttle position close to WOT with good results. With the classic small outer carbs and slightly bigger (CFM) main/center the outer progressives' can open at any position best for
drivability.. I can literally drive the 250 to the speedway with normal tri-power progressive setup and simply re-position two sliders on rods with screwdriver to transform to synchronous operation for the day ...
I also bult a Hi-Rise plenum for a big 2Bbl (500 CFM 4412) to sit on the Tri-Port adaptor. It was infinitely easier to tune , ran great from idle to WOT but
wasn't any faster ..
have fun