sorting out strombergs

Appreciate advice on a couple of point for a, formerly good running, twin carb 3.5. It's taken to running extra rich, black fog trailing behind, and won't go over 50 mph. Something is stuck of clogged. I'm thinking float valve or piston.

First, does it sound like something accessible from the outside? Please stop me from rebuiliding if it's not needed.

Second, I expect I will be going through both carbs so what rebuild kit can I get in the USA? The usual Rover parts places don't have em. Moss Motors has kits for CD175s on TR-250, etc. Is one of them known to work or close enough? What would be a good interchange?

Thanks.

Have you checked to see if the choke is stuck on?
Mine did this, the choke cable was returning fully so it looked like it was off but the linkage on the carbs was seized.

Good thought. I have the carbs off and the cold start linkage turns freely. I'll check the cable. Maybe something else was holding it.

I know lrdirect sell gasket/rebuild sets for these carbs. I had a look for my own vehicle. Just easier to order out of the UK.