Sorry I havent been on for a while.  Sounds like you found it.

But just one more thing.  Not only can the tank filter (sock) cause this, so can a small air leak in the line fairly high up on or near the tank.  It drops volume due to sucking air instead of fuel, but won't show a leak due to the higher location.

Also you need to watch for neoprene (rubber) hose.  A short section is fine, but longer sections can sometimes collaspe under high flow, and cut off the supply.

Neither of these seem to be any part of your problem, but I wanted to throw it in there for others who may have the same symptom.

[QUOTE=Adams' Apple]Sounds like you are on the right track, Wil!
There doesn't have to be any trash in the tank to stop up the filter there. Over time, fuel deposits will accumulate there, and turn to muck. I'll bet a new pick-up fliter will solve your problem. [/QUOTE]

another problem ive seen is collapsing lines..  an old worn out section of rubber line will collapse internally under suction..  looks fine from the outside.

The tank is now on my garage floor.  The strainer has what appears to be red rust clogging it.  My tank, with original build sheet on it, has an internal bladder.  The bladder has large cracks at both ends.  That is probably how the rust started showing up.  I assume there is no way to repair the bladder.  I'm having trouble finding a replacement fuel tank for the 78.  The hard decision is; I would like to keep as many original parts as possible but I don't want to pull the tank in the future if something fails.  So do I replace parts or not?  Metering unit looks good, it just has old rubber and a film of rust.  The tank does not leak but with cracks in the bladder it may not last long.  Fuel lines look ok except the soft connection lines that must be replaced.  My goal is to keep it as a reliable cruiser.  We just enjoy taking it out for rides.

You are right, no 78 fuel tanks to be found, so I'm planning to clean and reuse for now.  At the time I pulled the tank it seemed hard but now that the tank is out it seems easy.  Here are some of the leasons learned. 

The books say remove fuel lines to the metering unit before dropping the tank.  However, there is limited access to the lines.  So, what I did was drop the tank about 4 inches and then cut the rubber connection lines.  They are short, inexpensive and easy to replace after the tank is out.

The tank support rail is held in place with two bolts at each end.  The bolt heads are inside the frame rail and difficult to prevent from turning while loosening the nuts.  I made a tool with a socket, a piece of 3/8 key stock 3/4 inch long, a flat sheet metal wrench (dog) and some duct tape to hold it together (don't drop your socket inside the frame or else say good bye to it).  You'll understand when you see the small access hole on the side of the frame.

There is a fuel line clip inside the rear fender well on top of the frame member.  You can not see it, but removing it allows some flex in the fuel line during removal. 

Common sense, hydraulic jacks, patients and plenty of liquid wrench will take care of the rest.

  Thanks for all the help.  My bog problem is gone.  Two days of test drives and no more problem.

It was the strainer on the metering unit.  I cleaned the tank and replaced the entire metering unit (with a new strainer) while it was out. Problem solved.

Thanks again for all the help. 

Wil