1994 K75S Unblocking a blocked tank vent?

Jeff,

I was puzzling what would cause a chirping noise if the tank went under vacuum. A vacuum would pull the cap seals closed even tighter, so I doubt if that would be it..

Then a thought came to me (always dangerous..) - the high-pressure blowoff on the fuel pump is looking at "differential pressure" - ie - the difference between the input pressure and output pressure. When that differential pressure exceeds the force of the spring holding the blowoff closed, it opens and relieves output pressure.

In this case - the input pressure is the pressure in the tank. If your vent is clogged up and you're pulling a vacuum on the tank, that means the input pressure is negative, so the blowoff will start opening at a lower output pressure. Combine that with a partly plugged fuel filter - and it becomes obvious to me what is happening.

I suspect you'll be happy once you get your ride in

Brief test ride; so far VERY GOOD!

Late last night I rode a few miles on the freeway (60-70mph) to pick up my wife from work. On the way home we rode along the boulevards around 30-50mph and the bike seems noticeably smoother than ever before.

I think the combination of unblocking the vent, new crankcase breather hose, new fuel injector nipple caps and 5 other new fuel/vacuum hoses really made a significant difference.

Although I probably still need to get the valves adjusted the bike is now running better than ever. Now I finally know what others mean about the smoothness of the K75---nearly four years since I bought the bike!

Don, your explanation makes perfect sense and I also suspect that the chirping is gone for good. I'd be surprised if it started again.

The other good news is that my ABS system is back on AOK; the new ABS relay and a couple attempts to reset the brain took care of the warning lights staying on all the time.

Now I can't wait to take her for a nice long ride!