K75 won't start unless Jetronic CU unplugged

[bast1472]

Hello all,

I made the mistake of parking my 1995 K75 outside under a cover. Shame on me, I know, but I hoarded one too many project bikes and ran out of space in the moto shed. I checked on it about every 2 weeks to charge up the battery and take it out on a ride to make sure nothing would stagnate from sitting too long. However, the last time I went to take it out, I pulled off the cover and the bike was covered in mold. I gave it a good scrub with a mild bleach solution and it looks nice again. It's no longer parked outside, but after the mold incident it will no longer start. It will cough once or twice like it wants to start, but then it just turns and turns with no sign of starting and a smell of gas.

Today I tried ruling some things out, so I sprayed starting fluid into the air intake (no success), disconnected the forward fuel line in the fuel rail and watched fuel spray during startup attempts, and cleaned the contacts on the L-Jetronic control unit box and harness. I haven't checked for spark yet, but when I tried starting the bike with the L-Jetronic control unit disconnected, it would start and run for <5 seconds before eventually bogging down and dying.

My first thought is that moisture may have gotten into the box and wreaked havoc, but I haven't verified that yet. Is there anything else you guys suggest I check/replace based on these symptoms?

Thanks in advance!

[Laitch]

Is there anything else you guys suggest I check/replace based on these symptoms?

Check the fuel pump pressure using a T fitting in a line from the fuel delivery port to the fuel rail. Fuel pressure gauges are often loaned out by Pep Boys, Napa, AutoZone and some other major vendors for just a refundable deposit.

[daveson]

If the fuel pressure is low and not returning to the tank, I'm thinking one way it could run for up to 5 seconds with the fuel injection unit unplugged is if the injectors are constantly earthed, meaning constantly open injectors and gravity fed fuel. This would result in a rich mixture. If this is the case, keeping the revs high would mean the bike continues to run, not just for five seconds  but more than five minutes. I've run one of my bricks in this condition for over half an hour.

Your thought about water in the jetronic box is a good one, especially if you used a high pressure washer. If you think you can hear, or see signs of, water inside when you tilt it, you want to open it and dry it out, and the idle switch, and actually dry all the electrical stuff.