Quick update, for anyone who’s trying to solve the same problem: I got under the van for the first time since I started to properly understand how the cooling works (also delayed because it’s too damn cold out). Sure enough: no thermostat, no fan flap control linkages, and presumably no flaps in the fan housing. I think this explains my symptoms pretty well, because since I got the choke adjusted, it pulls away nicely for the first few minutes, then once the choke opens up it starts hesitating, which lasts until it’s properly hot. In other news, I have a nice new-to-me oil bath air cooler, with functioning gubbins and everything. Just need to get a barb welded onto the intake manifold . . .
That should fix everything nicely. As above, easy enough to drill and tap a fitting for the vacuum take-off.
When I changed to a progressive, I did the even cruder bodge of drilling a 6mm hole and JB Welding a piece of microbore copper tube into the hole in the manifold. A ten minute job that has lasted 50000 miles.. Which works because it is an aluminium casting. The steel tube of the stock carb manifold is probably better off drilled and tapped.
