2003 mercruiser 3.0 Alpha 1 gen 2 - stalls when slowly throtting up/down

[M2theB]

Just picked up a new to me boat. Boat is a 2003 Invader with mercruiser 3.0 Alpha 1 gen 2.
Sometimes to start it I have to pump the throttle a couple times and crank it with throttle around the 1/4 range to get the revs up and then throttling down after it starts. It idles fine once started but if I slowly shift into forward gear it starts sputtering and stalls out. If I push the throttle forward hard past that point it gets up and goes just fine. Wide open it purrs and drives fine. Coming back to the dock when I throttle down, same behavior. It starts sputtering and stalls out.
I checked the lower shift cable and it seems to be moving fine, no binding.
The starter was replaced last year by the previous owner. The condition of the spark plugs is not known.
Where do I start?

 

[Bondo]

Ayuh,..... Welcome Aboard,..... While checkin' the spark plugs, 'n doin' a compression test is always a good idea,......

In yer case, I'd start with changin' the fuel filters, addin' a canister type fuel filter, 'n if it don't run better with that, rebuild the carb,.....

I believe, yer runability issue is fuel related,....

 

[M2theB]

What am I looking for with regards to compression? What PSI?
Going to pick up new plugs and fuel filters and start there..

Thanks!

 

[Bondo]

Ayuh,..... Above 150 psi is a really healthy motor,.....

140/ 150 is a solid runner,.....

Below 100 psi is a rebuildable core motor, at best,.....

 

[M2theB]

Regarding the canister fuel filter. Is this in addition to the filter already there? If so recommendations on a decent one? Assuming I would add it anywhere along the fuel line to the current one?