Hi all, I recently purchased and installed a Sachs/Dolmar 3.4 engine on my extra 300 airplane. The engine was new over 15 years ago and has not been ran since. Upon receiving the engine I discovered a crack in the spark plug wire and promptly removed it, replacing it with a new 14mm wire and a ground wire coming from the CH ignition box. The engine did not want to run "open" and idled fine with a 22x8 and 22x10 JZ props. The engine surged and seemed to be running too rich from the start regardles where the needle setting were on the carb. This engine came with a HDA 23b carb so I located a rebuild kit for it and installed the new components in the proper manner. Fuel draw seems to be great and idle is fine with a sluggish transition fallowed by a surging burbly top end. Max rpms I coule achieve was 5400 with the 22x8 prop. I contacted Brison since they are familiar and helpfull with all engines and they suggested the small hole coming into the carb may be blocked or possibly gaskets misplaced within the carb itself. After dismantling the carb and cleaning with carb cleaner, small wire and high air compressor presure I have still the same problem. The spark plug seems to be building up lots of carbon followed by fuel spitting out the carb at higher rpms. I tried to use my hand as volocity stack and it didnt seem to help. Starting with the needles set 2 turns out and slowly adjusting from there the engine will sag when too lean and "load" up when too rich but the same sputtering surge at top end. The engine starts on the first flip of the prop and maintains a steady idle. I have changed the plug 3 times and use the recomended 32:1 breakin with ashless lawnboy oil and even cut it down a little to see if that would help. Timing seems to be on and I have adjusted it 5 degrees either way but no sign of clearing up. Spark is good with a new 4.8 volt battery which it suggested in the paperwork and fuel is steady to the carb. If anyone has had a problem simulair to this I would appreciate it if you could give me a idea where else to look for the problem. I wanted to send the engine to Brison but they consider this a chopped engine and prefer not to work on it. The engine was manufactured by T. G. MFG in New Jersey for airplane use in the 70's-80's and the ignition is the older brown box Ch ignition. Thanks and have a great day.