Elan owner with Strombergs here, so may be missing something Europa-specific - but on the Elan twink, the tube connecting the 2 carbs is very important as it balances the airflow across the carbs and siamesed intakes. An Elan without would run extremely rough, at best. But that is a metal tube not a rubber tube, so perhaps you're speaking of something different. Regardless, there is nothing wrong or problematic about Strombergs, and if Joe Curto rebuilt yours you can likely rule them out as the problem and I'd be thinking ignition circuit somewhere. They're pretty simple to work on and diagnose, so don't be scared to open them up and look around if you're concerned about fuel gunk in the bowl. How are they mounted? On the Elan twin cam, the mount needs to be flexible with a good viton ring between adapter plate and secondary throttle and with thackery washers or similar under the nuts, I assume the same on the Europa. A hard/fixed mount can cause fuel frothing which may also cause issues. Last, have you checked the damper oil?
Agree with your last thought on checking your points, as well as the rotor itself. Even if new check the cap carefully and try an old or replacement rotor, there is a lot of new junk out there. In my opinion, Distributor Doctor is selling the best quality distributor parts, if you need them.
