K75s idles but dies as soon throttle is applied

[surreybeemer]

My k75s was running fine and now all of a sudden it developed this problem where it will start and idle fine but as soon as the throttle is turned and the rpm reaches 2500 it sputters and dies.  I took out the spark plugs and they were wet with gas and dark black in color.  Looks like too much gas is pouring in.
Also the fuel pump keeps running with the ignition on even if the engine is not running.  I had the same problem earlier but it resolved when i took out fuel pump and re-assembled it.  I have no idea what fixed it at that time but the problem is back.
What components can cause the bike to run richer?  Temperature switch?  tps? air flow sensor?
And why the fuel pump keeps running all the time, what signals it to run like that?
Thanks!!

[franck]

Just a thought......I had a similar problem with my K75C (1985).  It had not been run for many years and idled but when I touched the throttle it died.  I tracked down the problem to the air flow meter - it was totally blocked.  If you have never done battle with the afm you may find this link useful.

I also remember testing the afm by checking resistance at the EFI connector  (pins 5, 7, 8 and 9) - I kept a hard copy but I can't find the link.
Best of luck
Franck

[Inge K.]

A bigger leak at the hose between the airfilter housing and plenum chamber would also cause this.

[Grim]

I agree. This sounds like a vac leak. Check all the hoses and boots between the AFM and the head. At the age of these bikes the rubber is all going bad