hey guys, as the title says im having trouble with the bike. it got stolen then returned (5yrs l8r) and ive fixed the thing up to pretty much immaculate. the trouble now is its very hard to start, has very poor response down low and just now when i started it - was backfiring/popping intermittantly. the carb is squeaky clean and have checked several times. i have done the yz timing but it ran fine afterwards. it was just all of a sudden this started to happen, random. the valve clearances are sweet also. the thing is sometimes it runs better than others, but the poor response is always there. could it be electrical or the ignition timing or something ? would the accelerator pump do this ? its still stock. any ideas ? cheers.