To add to my post on the FL-25 weedeater I am working on. I finished the conversion and ran it with the original carb, just to see what this single needle, non adjustable, carb would do. With a 16x8 prop, I got 7000 RPMs and a 3500 RPM idle. This is a main problem with all single needle carbs for RC, there is just not enough flexibility for our use. I then replaced that carb with a 2 needle carb having the same bore diameter, 1/2". This carb produced 7000 RPMs also but with a nice 2500 RPM idle and a bit better overall running characteristics, throttle response included. Then I installed a 2 needle ZAMA carb with a bigger bore diameter, 9/16", like I used on the 21cc weedeaters. The ZAMA gave me 7100 RPMs and ran great with nice throttle response. I suspected that I could get more by porting, so I opened up the exhaust and intake ports as much as I practicaly could within reason. You can go too far. I always keep from filing down to the top of carb pulse hole use for the carb pumping function. Now I am getting a nice running 7800 RPMs with the same nice sounding 2500 RPM idle. It sounds pretty good a t 7800 too, not like a weedeater at all. It would probably get to 8000 RPMs but it would be close to being too lean. I am well pleased with this lightweight weedeater now and I am going to quit messing with it while I am ahead. It could improve with time also, it was new, and only has about an hour at most on it now. By the way, it was easier to trim than the 21cc weedeaters also. After the running test, and while cleaning it up, I discovered the gasket under the spark plug was leaking compression, noticeably, so I fixed that, but didn't run it again. I think it is safe to say that a FL-25 modified like I ported this one is good for right around 8K with a 16-8. I am very pleased with it to say the least. I can help with photos of the porting if anyone wants to see how far I went. I did open it up quite a bit to result in 8k.