|Some research showed to me that
i would encounter fuel starvation at speed due to the CBR having a
vacuum actuated fuel supply. This is because that when the intake and
float bowls are at the increased pressure, if the tank is at the normal
pressure fuel will not be able to enter the float bowls.
#1 was to add a fuel pump to have a pressurised fuel supply line.
#2 was to plumb airbox pressure into the tank to equalise the whole
I hate wiring so i chose to plumb the tank. Luckily a friend had a CBR
tank that already had a VFR tank vent fitted. I disassembled the
tank breather and tested its ability to be a spark arrestor seeing as
it would be connected directly to the airbox, which was now without an
air filter. This was because I had revised the airflow into the
airbox with some
smooth bore clear hose and a straighter intake path to improve
efficency. Got it all together and it ran terribly. Turned out that i
was siphoning fuel from the tank to the airbox under heavy braking due
to the fact that the tank breather did not have the capacity to prevent
fuel from running out from the tank.
I then removed the breather setup and after some research realised that
the CBR did not require the fuel system pressurisation as it would not
be achieving speeds which would deem it necessary. Without the tank
pressurising setup the bike ran fantastic but at speed the bike leaned
out very badly preventing it from making decent power.
However i was getting to know my carburettors by this stage and i was
sure that the poor running was due to inadequately sized main jets.