Trying to get to the bottom of this.

I have an FL350 that runs great, very fast for about 5 minutes (after warming up). After giving it full throttle for awhile and racing around, it starts to bog down and even die unless I let off the throttle and give it time. Even after I let it sit for a second, it will usually start to bog again just a minute or so after.

Running 3 air hoses out of the air box, everything else is stock. Just adjusted the carb again and still no improvement. Compression test yields a lower result of 90 psi (via pull start with throttle wide open).

New fuel pump, fuel lines, fuel filter.

Any ideas?

Yes sir, I bet you are running out of fuel.
You need to get 4.5 oz in 10 sec of fuel flow out of your pump using the starter.
Remove the line from the carb and put it into a measuring beaker.
Turn the Engine over with the starter but NO ignition.
If it fails this test then hook the line back up to the carb and remove the return line at the tank.
Redo this test.
If it passes now then the check valve is shot. If it fails then the pump is shot.
It could also be corroded pickup lines in the tank. They must be clear.
Verify your carb float valve is clear and has no crap in it.
It could also be that low compression issue. 90 psi is to low in my opinion.
CO

Thanks! This is great. okay I'll try this. Do you guys have suggestions on increasing compression? Probably piston rings?

you may get lucky with just rings and a hone but in most cases it will take a new piston and bore job

You will have to do a rebuild.
You might just get away with a cylinder hone and new rings as long as your piston is still within spec.
If you have an original Engine with the original piston then you will be shyte out of luck on this though.
Wiseco on makes an 80mm piston (smallest) and the original was a 78mm with tapered rings.
Do you have a manual ??
Lots of great info in this thread: viewtopic.php?f=2&t=18393&hilit=manuals
Anything highlighted in blue can be clicked on and downloaded.
CO