okay so i did the carb swap, the fault follows the carb now cyl 1 and 2 arent working, float levels on both are the same

so i guess now the question is what is wrong with my carb, any tips or sugestions on what could be the problem?

That's good news!

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Okay so it sounds like there is fuel getting into the carb so the next step would be to take a look at the fuel delivery from the bowl onward, so you'll most likely need to dismantle the carburettor and give it a good clean and a blow out. You are looking for a blockage.

When you were running the engine did the two cylinders that were not working suddenly work again when you moved the throttle?

Before you do all that just confirm that your linkages are actuating properly on the carb and are fitted up correctly,

Determining what part of the throttle the two cylinders 'wake up' will assist to determine where or what component of your carburettor is blocked. Going by your diagnosis you are having trouble at the idling operation which can point toward (check option D first)

A) blockage in idling jets

B) blockage in the ducts from the idling jets

C) blockage in the idling feed holes.

D) the idle screws are screwed all the way down allowing no fuel to pass during idle operation.

Take a look at some of these diagrams:

Useful Diagrams

thankd s lot for those diagrams, im thinking of blocking off the coldstart entirely to eliminate one section of the carb, and il take the carb off again and double check that all the little tubes are clean, any idea as of what the best way to clean them is? besides the normal air compressor blow out witch i have done already? to be totally honest i was hoping the engine was at fault cos to me it would have been much easier to reseat valves or do a piston ring replacement, il keep you posted on the progress, but for now off to bed and hopefully get it sorted after work tomorrow

oh and the problem is at its worst between idle and half throttle, full out it runs cleaner but still has a massive powerloss

heres a couple of pics of my old SU setup

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Did you have a look at the idle screws?

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I'm not sure why you'd want to block off the cold start, unless it is damaged and stuck in the on position there is no reason to block it off......

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Normally compressed air does the trick very rarely would one have to open the galleys to clean, unless they intend to bore and hone them out for more fuel delivery (methanol etc).

To open the galleys you'd have to drill out the lead plugs at the ends of each galley and then reveal them ones you've done what you have to. A tricky process that typically require a professional/experience. But I'm not convinced you'd need to go to that extent just yet.

The Twin SU Setup looks very tidy, nice work.

Reason why im thinking some of the galleys are blocked is cos the idle jets are clean and the idle mixture screws have absolutely no ifluance on how the engine idles or revs , where as on the other carb it lets the engine die when they are fully screwed in, as per recommended on the 138's my starting point on the idle mixture screws were 3 turns out

thanks, im actually starting to miss my old su's lol