I'm with feral on this one. Carbs are the ducks nuts on these little engines and when they're set up properly they'll be perfect. No need for EFI. You'll probably need a full gasket and jet kit, whcih will set you back a few hundred bucks.
You need to find some dude who knows these old set-ups - don;t go to anyone else 'cos they'll never get it right.
My solex for my 18RG were done about a year ago and it was $700+, but the results were amazing - it was like a new engine and it's still perfect.