Hey everyone,riding along then it started backfiring and it stopped ,  I had the carb off and cleaned but same problem it starts for about 20 seconds then it dies and feels like fuel but it backfires like crazy .It feels more like fuel than electrics but I'm at a loss any ideas?

The above was written on my phone hoping that someone might have an idea while I was at the bike but now I am at home at my pc so a few more details - I had the bike repainted about a month or so ago - tank and mudguards - since replacing the parts I've had problems firstly the electrics were playing up ( lights, horn, starter etc  only the rear light was playing the game ) but once they came back on line the bike ran ok finally we found a dodgy earth and have repaired it - but as soon as that was sorted the bike stopped after a ride of about 10 miles - I pulled over and tried the starter again, it would fire up and last about 10 - 15 seconds and then die as if it was petrol starvation but accompanied by horrendous backfiring flames out of the exhaust and backfiring through the carb as well, I called out the RAC ( the equivalent to the AAA in the USA ) who tried to repair it and his idea consisted of revving the balls out of it so that the header pipe was glowing red hot but anything lower than warp 10 and it backfired and died, it sounded like when I had the old brit bikes and the timing was way out. After messing around with the idle adjustment and the air mix screw it went for about 50/75 yards of fairly noise and backfire free riding but it stopped and didn't go again which resulted in a fairly hair-raising 45 minutes being towed by my mate on his BSA A7 through the fairly busy roads of Birkenhead back to his house where we have been trying new spark plugs etc but the spark seems ok which I presume means the coil and igniter unit are ok we cleaned the carb which seemed to have a little bit of crap in it which looked like it might be the sanded down bondo from the tank (I have an in line filter which was free of crap  that could be seen by the naked eye). The jets seemed free of dirt but  there appeared to be a very small amount  of a putty like substance inside the carb but it was on the body rather than the jets or air holes etc. should I do an in depth clean of the carb before going on to other targets ? The carb is a mikuni which was  bought from lancer and is normally spot on, if anyone needs any more info please ask and I will try and supply it, cheers one and all

sounds like the Pilot jet is fouled, try the trick with the compressed air (don't let the jet get away from you) and see if that helps
Also check you petcock for proper function

OK another update I have blown through the carb with compressed air have replaced the starter relay with new the right hand switchgear with new the ignition with new and still the problem persists engine starts and when starter button is released the engine cuts out - I really am at the end of my tether - I am beginning to exhibit the early signs of madness lol. This must be electrical or...mechanical or..... fuel or..or..or perhaps god just hates me. Methinks soon the river Mersey will be home to another motorbike or rider perhaps both! If I post no more you will understand    goodbye cruel world :'( :'(.

Cheers for that SteveH will try later on today - the spark plug is new and it is sparking when the start button is depressed but will check the way you said more updates later thanks

Great news!  

Now get out there and Enjoy your rides - well maybe not this weekend but when it dries up eh?  

Mine is staying in my garage until this spell of wet weather passes over - at least its mild  

LOL spoke too soon - halfway home started bucking like a rodeo bronco, this went was on and off for 5/6 miles then it finally conked out ( I noticed that the rev counter was bouncing about as well - so maybe its the coil ?  ) I had a spare igniter in me pocket put that on and it still wouldn't start, the fuel seemed to be flowing ok and battery was good - and just for good measure as I had broken down outside a pub the usual drunk old man come along giving it  " I've been riding bikes for 50 years and the problem is you've been buggering about with put it all back as standard and it will work, youve got the wrong carb on it - the handle bars aren't right blah blah blah " for half an hour - just what you need at half past midnight when you know you'll be waiting two hours for a pick-up truck and you've spent 3 weeks replacing parts resoldering joints and getting covered in crap with your mate (who also has 50 years experience with bikes) and then finally when you think its sorted it does it again. Whats the soddin' point.

My response to old drunk: So why the F are you drunk in a bar instead of out riding your perfect unmolested factory bike right now? Piss Off