I had a go at changing the part throttle jetting.Look in there with a flash light, is your drill all the way into the jet? its not supposed to be nearly that large.Was your engine having an off idle lean condition dururing crusing? Like you step lightly on the pedal and it bogs a bit? If not, don't bother messing with the part throttle mixture. Look down the carb throat, there's a spray bar running across the top just below the choke. One or two small holes are drill in the bar. Those bleed holes allow a little air to enter, which controls the vacuum signal pulling fuel from the bar.Stick a fine strand of wire into the hole,(strip a piece of #14 stranded wire) tie it off to the choke.see if that makes any difference, sometimes it does. On a 261 I used two matching carbs of the larger size.Bolted them on unaltered with 57 main jets, on a heated manifold they carbureted nicely.I did reduce the high speed jet to .028 from the stock .035.The engine pulled cleaner at full throttle after that.
