The low end adjustment can be a bugger to adjust at times. If the engine is bogging going straight from idle to full power with a lot of exhaust coming from the muffler its a sign that the low end is set too rich. First lean out the engine's high speed needle until the RPM increases tends to die, then open the needle until the RPM returns and richen it just a few clicks. Now go the low speed adjustment and make small adjustments until the engine comes up to power smoothly from idle. If your too lean the the engine will generally want to stall out. Lastly re-adjust the high speed setting. Its a good idea IMO to fly on the rich side as it prevents overheating most engines lean out somewhat once airborne. I like just a slight trail of exhaust when load is put on the engine while in turns and during maneuvers.