Fuel Leak

[Acejones]

Its a 1990 K75 with 17500 miles. I recently purchased the bike and after putting a couple of rides and about 200 miles on it I found fuel leaking (copiously) from under the tank . I finally figured how to get the tank off (no fun) and cannot find any leak source. The insulation pad under the tank is soaked and coming loose. The four screws on the fuel pump plate are tight. Is it possible the pressure relief valve blocked and forced fuel out of said screws ? How can I determine whats wrong here ?

HELP Please !

[Burnszilla]

Check the corners where the welds are. They are know to rust and leak. Find a welder to TIG it. Make sure you take the fuel pump out first or you'll cook it with the welding.

[Acejones]

Don't know how aluminum can rust. The leak seems to be above the corners anyway.

[Gilly]

Steve is right. May not be your leak source, but the corners are low spots in the tank and over time you get little traces of water that collect and cause, well not "rust" but the aluminum corrodes and you can get leaks.
The foil insulation was never really bonded tight to the tank, so will seem loose. I'd check hose connections. If all else fails connect the hoses to each other and bench test it for leaks. Maybe the level sensor??
Gilly

[DrPaul]

Its a 1990 K75 with 17500 miles. I recently purchased the bike and after putting a couple of rides and about 200 miles on it I found fuel leaking (copiously) from under the tank . I finally figured how to get the tank off (no fun) and cannot find any leak source. The insulation pad under the tank is soaked and coming loose. The four screws on the fuel pump plate are tight. Is it possible the pressure relief valve blocked and forced fuel out of said screws ? How can I determine whats wrong here ?

HELP Please !The four screws hold the fuel level sending unit/power supply cable. There is an O-ring between the plate and the tank. I don't think a fuel pressure regulator failure could not cause a fuel tank over-pressurization problem; the high pressure would be confined to the system between the fuel pump and the relief valve. You probably have a small leak in the tank at the lowest point on the left side. And yes, aluminum does "rust"; actually it oxidizes in response to water which finds it's way to the lowest point in the tank and over time a pinhole perforation may develop. This happened to my 1987 K75S and I used a JB-Weld product to repair it. It has held perfectly for 3 months now! If you do indeed have a hole in your tank and decide to have it TIG welded it must be absolutely free of fuel and vapors.

Dr. Paul

[Acejones]

Thanks Dr. Paul,
I knew someone would recognize that aluminum oxidizes. I still am skeptical of a "pin-hole" leak as the tank quit leaking for about 18 hours, only to start again. I am well aware of the virtues of J-B Weld. I am going to go over the bottom of the tank with a magnifying glass and check it out.

Thanks for everyones replies. I'll be back.

[Bobmws]

Thanks Dr. Paul,
I knew someone would recognize that aluminum oxidizes. I still am skeptical of a "pin-hole" leak as the tank quit leaking for about 18 hours, only to start again. I am well aware of the virtues of J-B Weld. I am going to go over the bottom of the tank with a magnifying glass and check it out.

Thanks for everyones replies. I'll be back.

Since you have the tank off, and presumably empty, you can pressurize it through the filler with a rag stuffed around an air hose ( you do have a compressor?!). It doesn' trequire alotof pressure. Use some soapy water to find the leak.

[BuddingGeezer]

Thanks Dr. Paul,
I knew someone would recognize that aluminum oxidizes. I still am skeptical of a "pin-hole" leak as the tank quit leaking for about 18 hours, only to start again. I am well aware of the virtues of J-B Weld. I am going to go over the bottom of the tank with a magnifying glass and check it out.

Thanks for everyones replies. I'll be back.

I have a '87 K100LT. Three pin hole leaks in the left side weld. They were very hard to find. The symptom was wet insulation under the tank. Look for a tiny paint bubble. My holes were not aparent and almost drove me crazy finding.

I enlarged the pinholes, scraped the paint and rough up the aluminum with an electric engraver tool. J B weld. 1 1/2 years ago, 16,000 miles, temp from 15 degrees to 115 air temp and still holding.

Ralph Sims

[crgrbrts]

As others have mentioned, K75 series fuel tanks gave been known to crack at the welds. Once your problem is solved -- as it will be -- make SURE to replace the big rubber grommets at the rear tank attachment points (where the circlips are). Those act as shock absorbers and their inevitable failure after years of exposure are a known cause of tank cracking.

Craig
(who found this out for himself the hard way)

[Acejones]

I finally determined the leak was coming from the sending unit plate. Time to replace the o-ring.