My honda fireblade 1992 900rrn?

my bike runs fine for up to 6 or 7 miles,then suffers "fuel starvation" the petrol tap is in the on position & the tank is full of petrol.If I turn the tap to reserve,eventually it will start & run fine again.It is as if I am running out of petrol & need to go to reserve,but there is loads of fuel in the tank.Sometimes it will go 1 -2 miles like this,other times 6 or 7.Do I have a blocked or partially blocked "on position" fuel tap,but the reserve is ok?Do I need to remove the whole fuel tap & clean filters? or could it be something else