I am reading a lot of advice that is incomplete. After checking fuel lines and flow on a test stand and making sure glow plug fuel and valve settings are good, and checking for fuel and or air leaks there are a few things you must ask. What altitude do you live at? I live at 5000 ft elevation. The needle adjustments here are much leaner than at sea level. On a normally aspirated engine the carb has a set amount of air flow(air bleed carbs excepted). All we do is reduce or increase fuel flow to obtain proper air fuel mixture. Also at higher elevation more nitro helps with idle and transition when air fuel mix is correct. At sea level 10% nitro may be fine, but at higher elevation you may need 15% or more to run well when properly tuned. So you see you can't make blanket statements about nitro percentage. You didn't say if the engine was mounted inverted. If so fuel tank position and carb adjustments become more sensitive to keep engine running well. If the fuel tank centerline is above the carb fuel inlet you will tend to flood an inverted engine. Make sure your valve clearance is to spec also. You didn't say what size prop you are using and that makes a difference. Just because the manual says your engine will turn a certain size prop doesn't mean it will. I have rarely been able to turn the bigger size props even close to advertised RPM.( Due to power loss at 5000 ft elevation) If you have access to Clarence Lee's engine problem section in the mags try to read them. They are very useful. Good luck!