I have almost the exact same setup and almost the exact same problem. I have tried sooo many things with little luck. My 145 had a non stock gas cap that had a lock on it, so going with what has been said in this post and what others have told me, I grabbed a stock cap from the junkyard. There is also some thoughts on the charcoal canister being part of the problem. When my car dies, and I look under the hood all I can smell is fumes which makes the venting issue seem much more credible. I too am collecting parts for the SU swap, but if it's just the floater or the stupid canister, why spend all that money to get a set of SU's? I, like you, am stumped...

I'm that friend that KLR142 posted about. We tried a ton of stuff with little success. New pump, cleaned and lined gas tank, removed in-tank filter, fuel pressure regulator to ensure the carb isn't getting flooded with fuel, new accelerator pump diaphram... Now I'm trying stock gas cap and thinking about rejetting the carb or getting some SU's.