We have kits for the Triumph and BSA 250 singles and the Triumph Cub. The 250s use a 24mm and the Cub uses a 21mm. Performance is a very noticeable improvement over the stock AMAL carburetors. Kits include a manifold flange adapter and extra jets for fine tuning. Your throttle should work on the 250s, but I'm not sure about the Cub. It may need a new cable. To the right, select the kit you want and the shipping destination.
We have put a 28mm OKO on an A65 BSA 650 with a single carburetor, which is the Thunderbolt. This kit will also work for 650 Triumphs with a single carburetor. Jetting is adjusted for it. Twin carburetor kits are also available to select here. Just be aware that OKO only makes "Left hand" carburetors. Smoother idling, more power and throttle response are achieved with the OKO.
Mike Waller of Britannia Motorcycles helped us develop a kit for the BSA Goldstar. Starting is much easier with the OKO, as well as performance being much better. We use a 36mm OKO and provide extra jets and a manifold flange adapter with the kit
Sorry, we have no photo of the Vincent Rapide. We have a California customer we worked with to put two 30mm OKOs on his Rapide, so we are making this kit available to all. The kit is just the carburetors. If you need flange adapters you can add them.