Idle dies on hill and backfires on flat ground

[bvudsg]

I have a 1985, recently purchased with my wife about a month ago for a project.
The idle RPM was around 3-4K once we got the bike running(took about two weeks but thats another story).
After an oil change, spark plug change and gear oil change the idle went down to 1.5-2K.
Now to the problem.
We work on the bike while its on a slight incline facing uphill.
The bike idles well for about 2-3 minutes around 1.5-2k and then chokes out and dies.
When flat the bike idles fine for 2-3 minutes around 1.5-2k and then starts to back fire every 30 seconds.
I can only assume that the bike is running rich or lean, and or the bike has a vacuum issue between the fuel rail and the engine.
Any ideas? Ive been stuck on this problem for about 2 weeks.

Thanks
Cam

[Me Again]

I had a similar problem once and found the fuel filter plugged.
This would not be uncommon for a bike that sat for a while as you get rust and everything else clogging the lines.
I did have a problem that when I changed filter I did not flush the lines and clogged the new on up.