1998 50 mercruiser

I am having a problem with rea

I am having a problem with reaching WOT only gets to 4000 rpm. Lowered prop pitch to a 17 still 4000rpm. Also have a staling problem at idle while in water and some surging withut touching throttle. Does this sound like it needs to have a carb rebuild?

"Sounds like fuel starvation.

"Sounds like fuel starvation.
Could be filters, fuel pump, or carb.
I would start with filters, including the small porous media filter at the carb inlet, if equipped.

Rod"

"Follow Rod's advice. Als

"Follow Rod's advice. Also clean the flame arrestor on top the carb. When was the last engine tuneup performed; plugs, wires, cap and rotor?"

"all filters are new and so is

"all filters are new and so is fuel pump. so im thinking it is the carb. Also had fuel pick up out of tank, replaced antisyphone valve. Are there different antisyphon valves?"

Tune up right before last outi

Tune up right before last outing. New flame arrestor also.

Dean:

Is the engine carbed

Dean:

Is the engine carbed or EFI? What carb is it?

does your throttle open all th

does your throttle open all the way when selecting WOT?

"sorry I should have told that

"sorry I should have told that, I know better than that! It is a 2 barrel mercarb. I must add that it has been doing it for a while and I did rebuild the carb but it was the first one I ever did. But I followed the instructions perfectly. Butit could be wrong. Just want to get some advice before I take it off and take it in to get it professionally done. I am thinking of using a small tank to run it on to see if it changes too."

Yes throttle plates are wide o

Yes throttle plates are wide open at full throttle.

"Dean:

That carb is a PITA!

"Dean:

That carb is a PITA! Set the idle speed in forward at 650 RPMs. W/the engine off, turn the mixture screw clockwise until it just starts to stop while counting the turns. If you turned it more than 2+ turns then it is set a little rich. Back the mixture screw out 1.5 turns and start it. When it reaches operating temp. slip a 3/8" socket over the screw w/a black line on it near the 12 O'clock position. Wear a glove and S L O W L Y turn it CW until the engine misses ever so lightly. Remember that point and turn it CCW until it misses. Now try to set it between the 2 points.

The amount of miss or change in idle is so subtle that it is easily missed unless you do it daily. I used a vacuum gauge Sunday and had to read the metric CM scale to see any ledgible change."

I have put a vacuum guage on i

I have put a vacuum guage on it and foound that I have 15-16 at idle. Fluctuates between the two. Also have set timing to 10 BTC. Checked it a 2500 rpm and the advance was only at 15 is that too low? I thought it should be at 25 degrees at that point? My idle screw is set at about 1.75 turns.

Took an ohm reading of my sens

Took an ohm reading of my sensor in the distributor and found it to be 5.345 book says to replace it below 100 ohms so couls this be my advancing problem?

yes

yes