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Motorcycle Repair/84 honda VT700 C fuel pump not working

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Question
I have a 1984 Honda VT 700 C, is hard to get it started, but the fuel pump works fine when wired direct to the battery, just will not
run when hooked in to the system the way it supose to be, it works
some time than other times it dose not work. What tells the pump when to run and when not to run? I was told, there was a triger to let the fuel pump know that the engine was turning over. I want to thank you for any help that you may give me. This VT700 C is a real Bear! Thank you Clarence.

Answer
Hi Clarence,

These bikes use a fuel cut relay which is triggered by the spark unit or ignition
coil voltage pulse. It is a transistor unit which when triggered allows power
to flow through the relay to the fuel pump. Very similar to a mechanical relay.

The only difference is a mechanical relay is triggered by the grounding of
the relay by the computer module. These work the opposite way
by sending voltage to the transistor base when the spark happens
it switches the relay on and then some fused power from the battery is allowed
through to the fuel pump.

You should have power to the relay on a black wire I believe with the key on.
The blue wire goes to a spark unit and coil 1.
The black/blue wire goes to your pump.

When the coil sparks it sends a pulse to the fuel cut relay which
should activate the pump momentarily.

If you look for a relay with the above wire colors that will be the
fuel cut relay.

WS
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Wayne S.

Expertise

Licensed Motorcycle Mechanic, Knowledge of motorcycles from 1960 up, Japanese, British and most other brand motorcycle repairs.

Experience

Worked for Yamaha, Honda, Suzuki, Kawasaki British: Triumph, Norton, BSA Other: Most Scooters and Mo-Peds

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Canadian Motorcycling magazine article

Education/Credentials
Licensed Motorcycle Mechanic

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