I have been restoring my 1994 model and finally have the tank back on the try and run this bike.

The fuel tap diaphram looks in good condition and does not leak fuel when off, on or res

I tried this

Fuel tap on, the vacuum line from carb tank blocked off
the bike will start and idle, I plug the carb vacuum line into the fuel tap while bike running it stalls

If I leave the vacuum line connected but fuel tap off it will run

I have not inspected the carbs inside could this be a stuck float maybe?

thanks
tim

 

The vacuum activated petcock works by vacuum from the #1 port pulling on the rubber diaphragm in the back side of it.
You may have a cracked rubber diaphragm that is allowing a leak.

 

Hey TimBucTwo,

finally got the bike going and this is a little embarrassing
the bike I got was in pieces and nothing connected, and a lot of parts missing or broken
but the fuel line for the tank I connected a "T" I thought was missing to the top lines
which I realise now are the over flow so i was basically feeding fuel into the over flow pipes of the carbs
and while it was hard to start and ran ok I knew something was wrong
anyway connected correctly, vacuum line to tap and all runs great
I did remove the carbs and gave a goo cleanout before I realised I connected the lines wrong

thanks for your reply my CBR is running again yee haa