Corrosion. Endemic to the GL1000. In fact, this more than anything, even more than broken float pivot stantions, junks a carburetor. Because broken stantions is repairable. Corrosion, in all but the mildest examples, is not.
The GL1000 is susceptible to corrosion not because of ethanol fuel, not because of dissimilar metals, and really for no other reason than its metal. Until the late 1970s, Keihin made all their carburetors with an aluminum alloy that was rich in zinc. Production engineers will tell you when something is made of this alloy it is either for cost reasons (when it is almost all zinc, such as in children's toys of the 1950s), or due to the lack of advanced casting technology. Manufacturers with still-developing casting technology used alloys heavy in zinc because it flowed well into molds. It was easy to cast. Look at 1950s and 1960s BMW carburetors, Triumph carbs, and others.
A few years ago I compared a GL1000 single carb body, stripped to the bare casting, with a similarly prepared GL1100 carburetor. The two are very close in size (though the 1100 has a slightly smaller bore). Guess what? The GL1100 carb casting was lighter, much lighter, than the heavier GL1000 carb body, demonstrating the high zinc content of the GL1000 carburetor. The GL1100 carb alloy appears identical to that used in the DOHC fours, CBX, CX500 and others. Much more aluminum and less zinc.
GL1000 = 2 lbs.
GL1100 = 1 lb.
What does this have to do with corrosion? Just this. Remember what boats have on them? Sacrificial zinc annodes. The annodes take the brunt of electrolytic corrosion, theoretically leaving the other metal in the boat relatively free of corrosion.
So your GL1000 carbs are basically huge sacrificial zinc annodes. A little overstated, pethaps, but not far from the truth. After 40+ years these carbs are showing up very eaten up around their jet towers, as depicted in the image above. For this reason, I keep in stock a number of good replacement bodies for my customer's projects. More information at the links below.http://www.motorcycleproject.com/text/zinc.htmlhttp://www.motorcycleproject.com/text/c ... epair.html