Motorcycle Repair: wont start, motorcycle carburators, air passages

Question
Hello. I have a 1980 Yamaha SX400. I bought it from a guy who had not ridden the bike or probably not started it for 5 years. I have cleaned out the carbs and changed the oil. I checked for spark, which there was. I put a new battery in. I have had it running for short periods (1-2 min.) but can't get it to start most of the time. I was getting some backfiring and even with the throttle wide open it would not go above about 1500 rpm. I cleaned the gas tank out and put new gas in. It has the cdi ignition so no points.  Thanks, Peter

Answer
Hi Peter, Carb cleaning any motorcycle carburators is a very involved task. It has to be approached with a surgeons precision. The carbs need to be removed and completely dissasmbled. In a well lit area each Idle jet, main jet, Jet needle, Needle jet, Emulsion Tube, Needle and seat, float and Carb Main Body Air passages require careful inspection. Commpressed air is required to free up blocked air bleeds. I have had Jets so plugged that it took days of soaking and picking to get them clear. You should double check everything you have done with the carbs and make sure they are clean and clear of any blockages. To rule out an ignition problem, next time you can get it started have a can of carb clean handy. Remove the air filter. While you attempt to raise the rpms spray a bit of carb clean into the carbs through the air box, if it revs up with the carb clean then your problems lie there, if no change then we are looking at an ignition problem.
 let me know how it goes

Randy