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Roger Moss

Stans advice is sound but if you are still in trouble, go back to basics.
take the jet access nut off the bottom of the carb and measure how much fuel you are getting through per minute.
I would hope that you are getting at least 350ml / min
If not check what you are getting from the tap
I would hope that you are getting at least 700ml / min
If not, drain tank and take out tap.
Check if it has a filter that it is clean and check that there are no pieces of debris obstructing the tap.
For my engines I need two taps delivering 1000ml / min each and if the float chamber is OK I should get about half that to the carb bottom banjo.
ie 1000ml / min
Is is not uncommon for the carb to be starved by poor feed from rusty tanks etc.
Do check that the pipes and float chamber are clean and unobstructed.
If the bike has been “tuned” then you might have to knock the timing back between 5 and 7 degrees.
I do sympathise as after a good few years, you cannot always see immediatly if something has been altered.
My philosophy if I have problems, is always to start at the beginning, hence fuel flow. If that is given a clean bill of health, we can look further, such as is it always one side that seizes, are both plugs identical in colour, if not, their could be an air leak.
All good character building stuff!
Kind Regards
Roger Moss