3 way metal fuel line valve problems?

Anyone ever have a problem with a 3-way fuel line vale selector (metal valve assembly)? I have one in my boat that allows me to choose flow from the fore or aft fuel tanks individually, and/or a dual flow selection which is supposed to draw fuel from both tanks at once. My manual valve appears to not be drawing from both tanks when set at “dual” and it won’t draw from either tank individually when set at a single tank choice. I found out this weekend that it is only drawing from one tank when set at dual, which limited a travel situation out on Lake Michigan. As a metal valve assembly, I assume there is something more wrong with this than just a line clog. Anyone ever have issues with this type of valve before? Any advice?
I can tell you one thing, Skeeter didn’t make it easy to get this thing out….. This one is going to be a challenge.

Splitshot

it kind of sounds like you are only getting the valve to move partially through its range,is there a pin thats broke in the handle?? or the handle is possibly stripped out?? I would think that if it is able to draw from one tank that it would draw from the others IF it is swinging from fore,aft,dual.
as you mentioned,a couple of lines clogged,are there filters for each tank that could be plugged??
if it were me,select a tank,apply very little pressure back through the valve to a selected tank and see if you get flow that way,dont use high pressure as you may blow fuel out of the tank,or possibly rupture something,at least that way you could see if the valve is moving as its supposed to.

Possibly it is plumbed wrong? I’d disconnect all lines and confirm what each port of the valve does in each position of the selector handle.

Is this a new problem? Has the valve worked properly in the past? If it has worked in the past properly , then it surely is plumbed correctly.

I have seen pick up lines in tanks fall or break off, air sucks easier than fuel and causes no fuel to be pulled out of the good working tank then when in dual pull.

In this case, nothing is “new.” This is the way it came from the manufacturer and I’ve never made adjustments to any of the fuel line stuff – except for installing a Lowrance in-line fuel flow meter, which had nothing to do with this issue. That was also installed years ago. I checked all fuel lines and the tanks and tank wiring. ….Verified that all hoses and connections are good. My guess is that the manual valve itself is clogged, or it is internally twisted or off so that jets/holes are not lining up with the fuel lines anymore (how or why, I don’t know).
I talked to a Skeeter Service Rep. He said to try blowing air under pressure back from the main motor fuel line towards the tanks through the valve and see if there is a clog or non-operating valve. My other option is to skip the troubleshooting and just replace the valve, which I am tempted to do to save time for fishing. This is just an odd problem that I’ve never heard of before. Maybe there’s a Zeb in the line too….. Lots of AIS around ya-know.
Thanks for the input.
Splitshot.