The Ofna block is a great engine, but the carb could not hold a constant tune. The carb was made of plastic and when the engine got up to temp, they seemed to lean out and send the temps up. I remember when I had one I had to constantly keep tabs on the low speed and high. I swapped out that carb with a OS VG carb and it was constant set and forgett it! All metal construction and two needles. I liked the Ofna motor because it was a Hyper 8 and it has crazy RPM's.
Many people have the same complaint. They all switched the carbs and everything works great.
Motors like OS are more tune friendly.