OK here you go. I have one of these engines and it now runs great but it didn't always. I experienced the same problems as you. The first thing I did was put in a Champion RDJ7J plug. This helped a tiny bit. Then I went to an unregulated 5 cell nicad battery. Helped a bit more but still not good. I checked the timing and it was set at 10 degrees and it is supposed to be 30. The Halls pick up brackett was at it's maxium so I had to drill and file it to open the slots enough to move it and get my 30 degrees. This timing issue seems to be a problem with most of these engines. Now the engine finally came alive and ran without missing and backfiring. I still found it a bit hard to start and would not idle low enough for me so I purchased the RCEXL auto advance ignition ( mine came with the CRCC fixed ignition - black plastic box ). I also had to alter the Hall's brackett on this to get it advanced enough. I believe the holes are drill a bit off in the hub for the bracketts they use. I also went to a 4.8 / 4 cell pack.

Now the engine runs absolutely perfect. Starts easy, idles easy and turns an MSC 18 - 10 @ 7300 and an Xoar 20 - 8 @ 6900.

Some of the very new ones come with a silver ignition box which IS auto advance and uses only 4.8 volts. If yours is like this all you need to do is change the plug and adjust the timing ( I bet it's off ) and you should have a good engine.

Even though mine works great now in retrospect I would have been better off to buy something like a DL50 right from the git go