NO NO NO... Don't spray carb cleaner into the fuel tank. I don't know what you have over in Ireland, but you'll need bottled carburetor cleaner. Something strong like Chevron Tecron, or Barryman B-12.
You said in your first post, that you see gold slotted screws. Those are the float bowl drains, so you've already found them. I use a bigger screw driver for the head size, then ground down the sides to get it into the countersunk bore of the screws hole. They're in there tight and will make a loud snapping noise when you crack them loose.
You may get lucky and you can flush out the carbs. I've done it before, but it only worked once. But hey, ya just gotta try! More than likely you'll be pulling the carbs to clean out the pilot/slow speed circuit. Be aware that you're not gonna get all the crap out of the bowls just by draining...
It's faster to pull the carbs, clean and reassemble, than jerk around messing with the carbs for day's on end trying to avoid the inevitable.
