Thanks for the reply Wristpin I tested around the inlet manifold gaskets with WD40 but no change in engine note so looks like the new ones i fitted when i did the exhaust valve spring are all good.
Still convinced it’s a fault with the carb somewhere, Saturday morning again i stripped it down and this time put the housing in a pan of boiling vinegar for 15 mins, plus following the advise from the man in Amersham who sells numerous bits for the Ransomes Triple and seems to know a lot about them, i drilled out the 2 seals fitted to the carburetor after it was machined at manufacture. This should once an for all rule out any blocked air or fuel passages in the carburetor as i can now push a small piece of copper wire down every one to guarantee they are clear. I then drilled and tapped them with an M4 tap and super glued stainless bolts back to reseal them. It took me almost 3 hours including air lining and repeated spraying with carb cleaner and rechecking with a torch and air line that all passages were clear. I refitted it to the engine and it’s still got the same problem. !?!??
I then spent another 2 hours adjusting the governor and throttle cable positions as well as the throttle stop and idle mixture screw.
Whatever i seemed to do the engine runs at a good fast speed with the throttle butterfly in the carb fully shut. It runs on a bit and then after 20-30 seconds begins to die and is normally unrecoverable no matter how much you reopen the throttle. There must be fuel leak somewhere in the carb as with the throttle butterfly fully shut, only the idle or pilot jet should be allowing a tiny amount of fuel into the venturi in the carb. Only when you open the throttle butterfly does the main jet come in to play?
I’m going to draw a sketch of how the carb’s designed to try and better understand it.
