st70 petrol leaking from carb

petrol is leaking from the choke lever on my honda st70 1970 looks like its been tampered with before as the machine screws are rounded and its difficult to get them tight enough should I just replace the machine bolts if so where to source them from?
or is something more serious with the carb?

Check if changing the hight of the floater helps.
Also, check (by blowing in the fuel inlet and pushing up the floater needle) if the needle still closes fuel inlet once the bowl is full.

do I need to take the carb apart

YES
AND TAKE A PICTURE SO THAT YOU KNOW HOW IT GOES BACK TOGETHER

is there a specific height to float from the bottom of chamber on keihin carb or is just hit n miss

I don't know the exact height, but you can check by blowing in the inlet while slowly pushing the floater up.
The inlet should get blocked before the floater reaches the very top of the carb bowl.

I have tried different heights on the float but still leaks even tried to put a o ring gasket on the inside of the choke lever washer but still leaking petrol.
I now think the keihin carb is knackered. what can I replace it with? I have seen some cheap ones on ebay monkeybike/dax carbs. does it matter which carb as a replacement or can you recommend a replacement?

also couldn't get a year of manufacture letter from Honda UK how can I register with DVLA with the letter. Honda suggest a another but who?

After 6 weeks off the bike finally returned to a leaking carb and a flooding carb.

I tried different float heights but no difference so it whether to spend £25 for a full rebuild kit or does anyone know where I van get a replacement float needle

or a cheap Chinese replacement as not been able to find a Honda keihin replacement?

I bought a keihin carb off eBay, brand new, worked perfectly straight out of the box, £17 delivered . Just search st70 carb.

Pretty sure it's not an original one
That would set you back 10-20x the money.
There are some very good and affordable reproductions around.