if it feels like flooding check for flooding. It is common for the needle valves in the float bowls to fail. I reckon they don't like unleaded fuel. A Viton tipped version is available which seems to largely cure the problem, no idea who sells it in the US. If you either pull the air filters, or remove the pistons i n the SU's see if fuel is bubbling out of the jet, it isn't supposed to, it is meant to be drawn out by the vacuum of the engine running. generally if they do this they'll run OK on the open road but be a pig round town and at idle.

Aso check points, point gap, and timing.

Regards