I have had major problems with getting enough fuel for the high-end needle on both of my gas engines. My firt engine is a conversion ryobi that I bought from The Best Engines that came with a very small throat zama carb, the engine ran fine with this carb but I read in this form that a healthy power increase could be had by fitting a larger bore carb on it so I purchased a walbro carb with a larger bore. I picked up some good RPM gains but it would only intermitantly get enough fuel and it would not respond to the high end needle ie. sometimes it would run strong and sometimes it would just bog and die when throtle was applied. My next gas engine was one of the early DL 50 and although I have had this engine for over a year now I just started it a couple of weeks ago and I was unlucky enough to have one with the bad carb ie. no fuel to the high end needle. I have since purchased a new version of the DL and tried the carb from it on my older DL and that made the older DL run fine. So my next test was to try the new DL carb on my Ryobi conversion. At first the engine ran very good and I tached 6200RPM with a big Zinger 20"x8" prop. Then later in the day I tried it again to fine tune the timing on the electronic ign. and I ran into the same problem with getting enough fuel for the high speed needle again. I am getting a little discouraged with all the carb problems I have had so far as I have yet to have a flight with one of my gas engines. I would welcome any expert advice as to what ccould be causing my fuel flow problems.

r u moving in small moves i mean only a screw driver blade at a time and then retesting that is one big key to tuning a gas motor. set the H for max and then start working on the low. ONce the L is set go back and tweak the high it may need 1-3 screw driver blades at the most adjustment to achieve peak again and make sure the motor does not sag for a long run up on the grond long being about 15-30 seconds.....

If you've swapped carbs several times and obtained fair results one time but poor results another time with the same carb I don't believe the carb or the timing is the problem. Timing does not have to be dead nuts on the money for an engine to run acceptably. It can be off a couple of degrees and most people would never note the difference. It sounds more like you have a fuel delivery problem. It's not making the trip from the tank to the carb correctly. That's where I would be looking for air leaks.

Back to the Zama carb. Going with a larger carb will not always provide an increase in performance. Quite often you will experience a loss in performance. If the engine is a conversion then it likely had a carb that worked quite well in the original configuration. Many conversion engines have the same carb they started with since the conversion process did nothing or very little to internal components.

Go back through the fuel lines and see if someplace isn't sucking air.