ORIGINAL: Konrad
I don't think the new carb will help. Please remember that the engine ran great with Mx X carb and doesn't need the improved carb to run. Remember that these toy engines run great with fixed venturis. It sounds like you are having a fuel draw problem. This is he opposite of the way you discribed the problem earlier. The glow plug shouldn't be an issue if you are leaving the glow plug drive on. I have to ask since the needle may have been reversed could the carb's spray bar be installed upside down? The cutout (fuel discharge port) should be pointed towards the engine.
The new 2600 carb is an improvement with regards to midrange and transition. There is no improvement as far as how strong the engine runs or for ease of starting.
I'm still pretty new to the aircraft thing. The problems I was having before were the opposite of what I have now because the needles were reversed before. The spray bar is in the right way too. That was never taken out of the barrel. After the engine ran its first 5 minutes and started acting up, the crankcase was flooding out pretty bad. I had to dump fuel out of it twice. It is also not running "forward" on startup, either. It almost always starts in reverse (clockwise) even though I am flipping it counterclockwise. In that first 5 minutes of good running, it would correct itself and switch directions. After that, it would start in reverse and run for a few seconds and quit. Sometimes (just a few) it would start in forward, then switch to reverse and once or twice back to forward and/or stall. (forward being CCW and vice versa.) My K&B .65 would start backwards during break-in occasionally, but flipping the throttle a few times righted it and kept it going. <shrug> I don't know.. I will have to keep putzing with it. Any thought on the head shim deal? should there be one or is it supposed to be metal-to-metal fit?