It is too lean if it dies when held nose up -- or your clunk may be stuck at the nose-end of the tank, which ca happen if your plane got a bump on the nose, or is stored nose down. Either one will do it. If you engine is transitioning well, you are probably close to a good tune. Try richening it up a few clicks -- you may also have to slightly re-adjust the low speed mixture as well.

On the other hand, being an MDS, it may never run well -- sorry to be discouraging, but you would probably be better off selling it & buying something else -- almost anything else.