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Repair guides and support for motorcycles manufactured by the German motor group, BMW.

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Why wont 1985 bmw k100 stay running

have 1985 bmw k100. turn key, hear fuel pump. press starter, bike starts right up, then sputters and dies. then hear fuel pump again, will start right up again, sputter and die. when engine starts, i dont hear fuel pump. I have changed the ECU and the fuel pump relay.

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1 Answer

Most Helpful Answer

Too many causes to provide an "answer". On the K's the pump is wired off the level sensor.

I'd lift the pump out, disconnect both + & - wires (put hose over ends=no sparks) and directly put wires on the pump, - to ground & hold the + to the battery just as you start the engine.

This will parse a mechanical vs electrical problem.

If it runs ok, it's electrical: get the Clymer manual (M500) to trace power wiring.

If it still sputters & dies, I'd put pressure gauge inline of pump to injector rail. It should be ~38psi.

The regulator may be bad (pinch the hose of rail to regulator to see), but more likely the pump can't keep up.

I've build 3 K bikes from wrecks and worked on many others.

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bryan christensen will be eternally grateful.
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