Have you tried swapping out the ignition between them? There are a few things that will cause an engine to quit in flight, first, and most likely cause, too lean a mixture. What works good on the ground doesn't always work good in the air. Second would be cooling, again, what works good on the ground, doesn't always work in the air. Third, glitchy ignition box, and these are the worst to chase. Finally, and most rare, carb icing, or turbulence at the venturi.

The second and fourth can be mitigated with proper baffling, the first is just a matter of chasing needles until you get the most reliable idle, transition and WOT. The third can only be figured out by a swap out. My DLE20 is also finicky, it can run great for a few flights one day, and thinking you got the needles nailed, doesnt run well at all a week later. It is a few years old and has the funky ignition box that high idles then transitions down, making landings a PITA.