Cdi Unit Restoration For A 87' Vfr 700 F2

The tach and fuel pump work together, at least on the 86 bikes. You have to have the tach wire from the ignitor box plugged into the fuel cutoff relay for the tach and fuel pump to work. The pulses from the tach signal wire tell the fuel relay to supply power to the fuel pump. The faster the rpms, the faster the pump works. The pump still only delivers what is needed by the carbs, though. It is only a 1psi pump, so when the floats close, the pump stops. Temporarily bypassing the relay delivers full 12v to pump and is a good way to prime carbs that are dry.

Edit: I think the 87-89 bikes get the signal for the fuel pump relay from the #4 coil wire.

 

Re the above: pump is 3 psi.

All my bikes run with the pump relay eliminated and a jumper wire across its plug. Much easier starting and less battery drain on bikes that are only ridden occasionally.

 

Are you sure 3psi? I've read a few places they were only 1psi and where one fellow swapped in a 3psi pump, but regulated it down to 1psi. You don't need much pressure at all. As soon as the carbs fill you want the pump to stop.

As far as bypassing the fuel safety relay, why? Don't you want the pump to stop when the engine stops, like in an accident for example?

Why would bypassing it make it easier to crank?

Why would it have any effect on the battery?