Do these motors smooth out with time? I have been opening the low-end needle to get a good transition, but now the motor runs really rough at 1/4 throttle till 1/2. The high end is fine. Does opening the needle richen? Throttle response is good going from idle to full but from full to idle if done quickly causes the motor to stop with a huge shutter. I can keep it running if I bump it to 1/4 then down to idle. I dont have much more than an a couple of hours running the motor, it idles at 1500 and will hit 6,000 with a wood Bolly 24X10. It will idle all day and pulls like a Mack truck, the transition is great, I just dont like how it runs at 1/4 throttle (lots of burbling and vibration). I blanced the prop prior to the run-in. I mixed the fuel at 30:1 using the supplied oil.