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Louie, Technician
Category: Motorcycle
Satisfied Customers: 12658
Experience:  25+ yrs. experience
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Bike will start, then imediatly dies, yes. shall i go

Customer Question

bike will start, then imediatly dies
JA: Will the headlights turn on? Is the battery fully charged?
Customer: yes. shall i go through every thing i have done
JA: What is the model/year of your motorcycle?
Customer: 1985 bmw k100
JA: Are you fixing your bike yourself? What have you tried so far?
Customer: yes. changed starter switch. fuel pump, fuel filter, fuel pressure regulator, fuel pump relay, hall sensor, mass flow sensor, ecu, under seat computer. cleaned all injectors, cleaned fuel rail, cleaned under tank ground.
JA: Anything else you want the mechanic to know before I connect you?
Customer: think thas it
Submitted: 9 months ago.
Category: Motorcycle
Expert:  Louie replied 9 months ago.

Hi and welcome to the site, I’m Louie. Sorry you had to wait awhile but I’ll do my best to help.

Initially, have you checked the spark plugs?

Still, let's check/review the basics. Proposed preliminary tests (if have not been done) after the " will start, then imediatly dies...":

  • attempt to start again (even if it will not catch/run);
  • work the throttle as if flooding the engine;
  • carefully remove the spark plugs;
  • note if the tips are wet with fuel;
  • cautiously perform a spark test.

The above would determine if the issue is electrical/ignition (least likely) or fuel delivery/starvation (most likely).

Customer: replied 9 months ago.
spark plugs are firing. when i turn the key, the fuel pump primes, as i press the start button it stops, engine starts then fails, then the pump turns on and primes again. then bike will start again. it will do this over and over.
Expert:  Louie replied 9 months ago.

Have you checked for consistency of IGN+12V to the fuel pump motor? ...and if it has good ground connections?