what to check?

[indyblue]

When I get to less than 1/2 tank of gas, it stutters while cruising between 2-3000 rpm just holding speed when a light load is on the engine.  Throttle response is excellent otherwise, no hesitations and runs good while cool but gets worse hot.

Carbureration?  I have seen mention of a fuel pump on this site, does an 84 1100 have a fuel pump?

[Arnie]

No fuel pump till '87, I think.  Your problem is likely hose routing.  Check that it is exactly as per diagram and that there are no kinks or twists in it. 
Could also be that the fuel cap is not venting.  To check that try opening the cap and see if the poor running continues.  IF so, then dis-assemble the cap and remove the flapper valves.

Cheers,
Arnie

[FJmonkey]

Are you running with a tank bag? This adds to any cap venting problem if that is what you are having. I had a venting problem but only when I had a fully loaded tank bag pressing down on the cap. I don't make the long runs anymore and don't have the vacuum lock problem either.

[indyblue]

Well, if it ever stops raining around here, I will check out the cap vent.  I don't have any bags or anything on my tank for that matter.

Thanks for the replies, hope to test the vent theory soon.  I have ruled out moisture (my first thought) by adding Heet to the tank and some injector cleaner.

[andyb]

Sounds like line routing to me.  With more gas in the tank, there's more force pushing the gas down from gravity, and it's doing ok then.

[indyblue]

Well, I guess it's time to check the line routing as there are no flapper vales in my cap.  There is only a tiny check ball valve and it is free and open.  The cap on an '84 is very different from the others, certainly nothing like the gas cap assembly file in the files section.