Pulled my 1990 GS out of storage (spent 6 months stored; carbs bowls drained.) Turned the petcock on; fuel went to the fuel filter, but no farther. Opened the drains on the carbs; they're not getting fuel.

The bike's not running a vacuum petcock; I altered it instead to a simple off/on arrangement using the stock unit and capping off the vacuum lines. I'll do more work to check fuel flow past the petcock, but for now it seems like the floats are stuck in the "up" position.

Any ideas on why they're not filling that I missed?

Filter got sludge up while in storage? Simple test would be to just hook up a line directly to the tank. Find the faulty component one by one.

That's next step for this weekend... isolate the problem.

What's odd, to me, is that the carb floats seem stuck shut. Typically the problem I find on bike carbs is that the floats won't close. When I went to open the petcock, I wheeled the bike outside and stood ready for it to leak gas on the pavement. Obviously that didn't happen, and opening the carb drains showed them empty.

I'm looking for any insight into why they wouldn't fill given a supply of gas (if the filter's plugged it's not getting gas, but I can see that the filter's filling.) There is a vent tube on the carb that can plug and prevent fill, but I've checked that already.

Have you tried giving your carb bowls a gentle tap with the wrong end of a knocking stick?

Store them full of fuel, the float/inlet valve sticks up and starves for fuel.  Store empty, the float can stick down, but usually floats again in the flooded bowl if you rap on the bowl with a dowl rod a few times modestly.  I have seen recently an old Evenrude Lark V outboard (1960's) stored for 30 years empty and the float was stuck upward --- go figure.  We got it running, but not well -- yet.  You may have clogged filter or shut off valve broken or damed-up.  I often think its better to store tip-top full with stabilized fuel (or WD-40 long term) than empty due to tank rust and residual fuel going funky.

prs

I've tried tapping on the carbs; didn't help. I can pull the bowls in-place (God bless allen head bolts) and see if they're stuck in the closed position. Just seems odd they'd both get stuck that way.

how much gas is in the tank?  if its not all the way full, I would try that first.  while your at it, go ahead and replace the filter, shouldn't be more than a few bucks