93 Merc. 4.3LX - RPM Surging above 2800RPM

First post and thanks in advance for your help.
I have a 93 Rinker Captiva 209
Merc 4.3LX, Alpha One Drive

This year, out of nowhere, I noticed my boat would drop from 3000RPMs to 2800RPMs for a brief moment (3 seconds max) and then go back to 3000RPMs. It does this randomly. If I drive it at WOT, I can hear what I think is the carb start to pop.
It hasn't stalled and hasn't been difficult to start.

Work already performed:
1) Cap and plugs...improved starting, but didn't change the surging
2) Fuel quality checked out okay...no water
3) Cleaned carb, rods were gummed up...improvement, but still a slight surge
4) Mechanic says engine is air tight

My boat mechanic, who is very reputable and trustworthy, is scratching his head as well.

Is there something we're missing?

Thanks again in advance.

Re: 93 Merc. 4.3LX - RPM Surging above 2800RPM

Certainly sounds like fuel starvation. Check non return fuel valve and tank pick up.

Re: 93 Merc. 4.3LX - RPM Surging above 2800RPM

Sounds like new spark plug wires would help, especially if you already noticed a change with new spark plugs.

What did the old spark plugs look like though? Fouled?

Re: 93 Merc. 4.3LX - RPM Surging above 2800RPM

Fun Times said:

Sounds like new spark plug wires would help, especially if you already noticed a change with new spark plugs.

What did the old spark plugs look like though? Fouled?

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The rebuilt carb created more improvement than the plugs. Plugs looked okay, a little corrosion in cap but not too bad.

Took it out today. Still surges, but much less frequently.

Thanks again

Re: 93 Merc. 4.3LX - RPM Surging above 2800RPM

Did you replace the fuel filter?

Re: 93 Merc. 4.3LX - RPM Surging above 2800RPM

Watermann said:

Did you replace the fuel filter?

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Yes sir. Replaced the filter when the carb was rebuilt. Checked the pump...working normally.

Re: 93 Merc. 4.3LX - RPM Surging above 2800RPM

downtownkenny said:

The rebuilt carb created more improvement than the plugs. Plugs looked okay, a little corrosion in cap but not too bad.

Took it out today. Still surges, but much less frequently.

Thanks again

Click to expand...

Ayuh,.... Welcome Aboard,.... Sounds like ya still got a fuel delivery issue,...