hello to all im new to all this

i have recently bought a r reg thundercet not run for two years done all that needed doing but its only firing on 1 2 4 it was firing on 3 4 at first but after blasting air through carbs it now runs on 1 2 4 i have spark on three and carbs have all been cleaned so theres no reason why fuel shouldnt be getting through any ideas

Are you getting a spark to #3?

It may be a dodgy plug or HT lead.

I assume from the post that you have a spark on ALL 4 plugs?

If so then I would suspect lack of fuel to number three which could be blocked jet or a valve problem - I suggest you do a compression test. If you haven't got a suitable gauge then put your thumb over the plug hole - if there is a big difference in compression you will feel it.

I had a similar problem with my GT550 couldn't figure out why it wouldn't pull fuel in 1&4 until I found the valve clearances were a mile out and the valves wern't closing - new shims and it's all sorted now - but it had me scratching my head for a while.

Good luck.

:D