Air Compressor Volume. CFM. And stuff

I have an air compressor in my garage (I should really have some sort of specs before starting a conversation) with a tank that is about 3.5 feet tall and maybe 18" across.  Runs on 110v.  It has what I call a "capacity" problem when I run a tool like a whiz wheel for any length of time.  Tool starts at full speed and almost immediately starts to slow down. It can pump up and easy 130psi at the gauge on the regulator.  Under the regulator is what looks like a stub of 1/4 inch pipe between the regulator and the tank.  So the question is:  Would it be worth it to change out the regulator and drill out the tank for a 3/8 pipe to flow more air?  Or do I need a bigger tank?  Or both?  I do have a bigger tank from an old compressor that failed.  I could run them in series to increase capacity but I realize that the compressor I have might not have enough refill rate.  And no, I can't just run out and buy a new bigger compressor.  

That size tank is probably ~30 gallons.  You don't need the whole 130 psi to run tools( I used 90 for mine).

What is the pressure when the compressor kicks on while in use?  Mine would kick on at 80 psi and run back up to 130 psi and then shut off.  Tools that use a lot of air will benefit from a larger tank for more reserve.

Adding the larger tank will give you a longer run time but will also make the recovery time longer.  The only way to fix that is with a larger(more capacity) compre$$or.

I would add the extra tank and see how that work.  That is also the cheapest way to go.

Is the compressor kicking on when the tool slows down? If not maybe the hose isnt flowing as much cfm as you think. 30gal sounds like something that should be big enough that you dont experience 'starts at full speed and almost immediately starts to slow down'.

Can you post a picture of your compressor?

I have an allegedly 5hp (but realistically 2hp) oil-less compressor where the motor bolts directly to the compressor.  The pump looks vaguely like a Briggs & Stratton.  It is louder than the depths of hades, but it cannot run higher-volume tools like my air sanders, zip disk, air hammer, drill, or paint sprayers.  It's fine with an impact, limited air ratchet use, and that's about it.

If you have an oil-less compressor, there might not be much you -can- do.

What is the duty cycle of the compressor?

Many smaller compressors are rated 50% duty cycle meaning run time on = run time off to cool the compressor pump. Ex: 5 minutes on/ 5 minutes off. Just because you can fill an auxiliary air tank doesn't mean you should. Unless the compressor is rated continuous or 100% duty cycle follow the compressor duty cycle rating.