I just did a compression test and I got the following readings:
Cylinders 2 & 4 Port Side 108 psi
Cylinders 1 & 3 Starboard side 82 psi

The engine runs good most of the time. If I keep it at 4000 RPM's and under
how much longer can I expect to motor to last?

I cannot afford a rebuild this year.

Appreciate any help.

Have you checked the starboard side head gasket? You might get lucky.

As suggested, check to make sure its not the head gasket. After that, its a crapshoot how long it will last. All depends on what is causing the low compression on that bank of cylinders.

I'd crack it open, hone and re-ring. Not very costly at all, and actually a pretty ease job. Clean carbs after to make sure you are getting proper fuel to the cylinders. Might end up getting quite a few more years out of her.

Shoot some wd40 in the cylinders with low compression, then do a test. If it raises the compression then it's not a head gasket.
If it stays the say then inspect hear gasket.

Okay just redid compression test and these are the new results

Cylinders 2 & 4 Port Side 108 psi
Cylinders 1 & 3 Starboard side 88 psi (up from 82 psi from previous test)

Did what Alumacraft 14 suggested and the Starboard side came up 4 points to
92 psi on both cylinders.

Do not know what else I can do cheaply till I can afford to start replacing things on it.
I did install a water/fuel separator. Idling much higher now (after I made some adjustments) like 1100 in neutral and 700 in gear. But still cuts back once in a while to 300 rpm and then dies. Always starts right back up easily.

PanoPaul thanks for your suggestion but that is out of my expertise and I am sure I do not have the right tools to do a job like that.

Appreciate everyone's input. Thanks

That's a pretty high idle speed...hard on the LU gears when shifting into gear.