Derek, The carbs were rebuilt by a reputable person 15 years ago & they were used for a maybe 3 summers on my 1800, then placed on the garage shelf since I modified another engine with another set of refurbished SU HS6 carbs with SM needles and have been operating that setup from that time on.
So, I acquired this '67 144 with 67K last year with a BW35 that was removed and I switched it to a M40 manual. The back carb adjusts like it should with a 1/16" lift on the piston affects the tuning factor so that is dialed in and just fine. The front carb doesn't do anything bringing the damper piston all the way to the top without affecting anything at all. There is no binding either,,,it drops with a small clunk. I use ATF for dampening fluid. When it gets a little warmer outside I will take a look at the condition of the front jet and maybe replace it with a new one that I have in the drawer.