Fuel tap and carb problems on GS850G

I haven't used my Suzuki GS850GT since February and after putting it the bench to do the oil and filters I found the crank case had filled with petrol via cylinder no 4 which was still half full of fuel. Luckily I didn't try to start the bike The vacuum petrol taps on these bikes are crap and I intend to blank the vacuum pipe to the carbs and fit a gravity fed petrol tap that means I will be able run the carbs dry when I park the bike for any length of time and generally not worry about fuel leaking from the bike (which has happened before).
My question is how did so much fuel manage to run through a carb? Do the float heights need resetting or did the amount of fuel the poxy fuel tap leaked through just overwhelm the carbs?

I'd have thought that if the float valve was closing correctly you wouldn't have a problem - the fuel tap can flow enough for WOT, but you don't expect the carbs to overflow at idle. Bit of crap in the float valve seat? Dodgy float valve? Wrong float height?

Not that a manual off petrol tap is a bad idea - IIRC the diaphragm taps were happy to fail either open or closed, have a feeling riding around on prime means you have no reserve?

On the Suzuki carbs the float valve assembly seat is screwed into the carb body (brass insert) beneath it there will be an O ring (part nos 13374-44080).
With age and modern fuels these nitrile parts deteriorate and the petrol actually flows around the seat and bypasses the float valve and runs into the engine.
I've had this happen with a 1984 gsx 750, a 1995 import 400 katana and a mid 90's Rf400.

My sisters Triumph Legend TT did it as well. We had to do an oil and filter change and fit a clamp to the fuel line when we noticed how high the oil level was.

Neil W said:

On the Suzuki carbs the float valve assembly seat is screwed into the carb body (brass insert) beneath it there will be an O ring (part nos 13374-44080).
With age and modern fuels these nitrile parts deteriorate and the petrol actually flows around the seat and bypasses the float valve and runs into the engine.
I've had this happen with a 1984 gsx 750, a 1995 import 400 katana and a mid 90's Rf400.

Click to expand...

Thank's Neil and everyone else for your answers. The petrol tap has a prime position which allows fuel to flow without the engine running that can flood the engine with petrol, that has caught a lot of people out. The On and Reserve positions are ok when the tap is working but my tap seems to have allowed the petrol to flow into the vacuum pipe and into the carbs and then into the engine.
I think I have sourced a gravity feed tap (Pingle) it's not cheap but I just want something with an 'off' position so I can run the fuel in the carbs down a bit and leave the bike for a week or two without worrying that 3 gallons of uunleaded will end up in the engine or worse still all over the garage floor
Hopefully, the petrol hasn't damaged any seals inside the engine.