Sounds like the carbs are not adjusted right. In particular the idle mixture screws probably need some tweaking.
Which WAY they need to be tweaked depends on how the carbs were adjusted in the past and what mods are on your bike.
If you're happy diddling with them and know what to feel for in how it runs then you can play with them yourself. But the quick and sure way to "fix" this is have a mechanic that's also a good tuner do the work.
Also depending on how often and how long the bike has been stored for over the years the carbs may be dirty and need cleaning. Similarly it's just possible that this is a new issue to go along with the maladjusted carbs. Like rust in the tank that is clogging the carbs. And then it's just possible that your petcock isn't opening properley. For that you need to disconnect the hose and see if it can flow out a liter per minute or more of gas.
Lots of possible things but not enough info to go on from what you typed. And it's difficult to say if it's rich or lean at this point without hearing more about how it runs at idle and when pulling away under light throttle. I've written that description of what to look for before. See if you can search for it with "idle mixture adjust" as the keywords.
Which WAY they need to be tweaked depends on how the carbs were adjusted in the past and what mods are on your bike.
If you're happy diddling with them and know what to feel for in how it runs then you can play with them yourself. But the quick and sure way to "fix" this is have a mechanic that's also a good tuner do the work.
Also depending on how often and how long the bike has been stored for over the years the carbs may be dirty and need cleaning. Similarly it's just possible that this is a new issue to go along with the maladjusted carbs. Like rust in the tank that is clogging the carbs. And then it's just possible that your petcock isn't opening properley. For that you need to disconnect the hose and see if it can flow out a liter per minute or more of gas.
Lots of possible things but not enough info to go on from what you typed. And it's difficult to say if it's rich or lean at this point without hearing more about how it runs at idle and when pulling away under light throttle. I've written that description of what to look for before. See if you can search for it with "idle mixture adjust" as the keywords.