Can't promise it'll fix your issue to be honest, but I hated that Encarwi and have had smooth sailing with the Dellorto SHA 15.15 ever since I put it on. Here's the intake, which hurts to spend that kinda dough on, but MLM is quality stuff. You should get a lot more reliable of a bike by doing this. I've never heard of anyone being disappointed with this particular upgrade.
As far as where you'll get flow on that Encarwi carb, I really can't help you too much with troubleshooting it because mine has been sitting in a box for...well...a while. I never could get that carb to work correctly.
I haven't got down to doing bearings/seals on this motor yet it's a planned winter project for me since this is one of my more reliable (albeit slow) bikes. I do, however, have the bearings and seals on hand as a local place here in Minnesota called Ickler was able to source them (and for all the other moped engines I've worked on) for me. I know they'll ship too, so if you get desperate you can contact them, their pricing was pretty good.
My setup is an '83 Trac Eagle with the Daelim M56 clone (same as the Laura M56 found on the Batavus, or at least everything is interchangeable between them). MLM People's pipe, SHA15.15, MLM reed block.
Here are a few pics, specifically some close ups of the intake/carb.
One thing I should mention with this motor is that you're pretty limited. I've just about done all you can do to it as far as bolt-on upgrades (carb/exhaust/reed block). There are no kits so if you expect to go beyond 35mph, you probably want to get a different bike, this is a just a cruiser, though it's been quite reliable as I mentioned since putting on that carb.