I hade the OPS MAXI 60cc twin for some years. It did not had the original Del-Orto carb. but had an homemade slide carb. with a separate Mikoni pump. It was ok on power, a little stronger than the STG4500 which it replaced but it dropped a cylinder sometimes in the air and caused me to land.
Important is to use the correct fuel which is maximum of 5%oil and methanol for the rest. I only benchran my 30cc:s with tuned pipe and the original Del-Orto carb. for a short time and it seemed like they had great torque easily turning an APC 20x12 prop.
If the Del-Orto carb is not working well, and difficult to find parts then i think another 90-120 carb. can be fitted to these engines.