Topic: 1987 Shadow VT1100 fuel pump

[Patrick]

I'm hoping someone can help me with a vexing problem I have with a project of mine. I picked by an '87 Shadow VT1100. Very nice cosmetically, doesn't run. I traced the problem to a lack of fuel. The fuel pump is not pumping. The PO swears the pump works, but he said the pump relay is shot. So he wired it into the harness using the blue/yellow wire from the spark unit as the only power source. He said this allows the kill switch to be used to turn the pump on and off. This L/Y
wire is connected to the black wire main lead from the pump and a black and yellow wire from the pump whose purpose I haven't identified yet. The black and yellow is not on Clymer wiring diagram at all. Here are my questions:

1. Why does a hot wire run from the spark unit to the fuel pump? What does this wire do? The wire from the sparker is now the only hot wire into the fuel pump. The L/Y wire that runs from the fuel pump that this wire normally would be connected to is not connected to anything.

2. This fuel pump had at least two hot wires running into it - the wire from the sparker and the main black wire hot lead. It isn't pumping now. Does it need both hot leads to supply enough juice to operate?

3. Anybody have any idea what the black and yellow wiring coming from the fuel pump is for? There is no corresponding wire in the connector the fuel pump harness attaches to, nor does it appear on the Clymer wiring diagram. This wire is now connected with the black wire from the fuel pump to the wire that runs from the sparker. Unless I know what is does, though, I'm not sure what to connect it to or whether it should be connected at all. There is a fourth wire, the green ground wire, that is properly connected from the pump.

4. I have considered the possibility that the pump isn't working because the fuel lines are not connected right and the pump might be pumping toward the tank instead of from it. Without pulling the pump, which requires disassembly of the entire rear end of the bike, how can I tell which line goes where?

Fuel pumps for this bike are quite expensive. I don't want to replace it unless I have to. Can anyone offer any insight that might help me make it work?

Thanks in advance.

Patrick

[tsflstb]

I don't know much about this as I'm messing with my first fuel pump also.  I've got the opposite problem - fuel pumping out of the carb overflows.

There may be some sort of low level shutoff going to your fuel tank to keep the pump from running with no fuel.  My FZR has a toggle switch that acts as a reserve.  Those extra wires may be something like that.

[Bodi]

Clymer manuals are (in)famous for leaving the really interesting stuff off electrical drawings. See if you can get a look at a real factory wiring diagram.
Fuel pumps are usually driven by the ECM in EFI injected engines, this is a safety function so that the pump is shut off should the engine be stopped - in a crash it might be pumping fuel into a fire (not good). Older cars had mechanical fuel pumps driven from the engine, same effect. Many cars with electric fuel pumps and carburetors have rollover switches that shut the pump off should the vehicle get upside down.
Anyway, I think your bike has carbs but no ECM so probably the fuel pump is controlled by the ignition module which should know if the engine is running as it will be firing the plugs. It's possible that the module cannot provide enough power to run the fuel pump and that's why a relay was used.