My Mercury is sick

[Racingfan]

Mercury
Model 200L Carb
Serial OT834340

I bought this boat 2004 Procraft 200 Super Pro about 4 years ago. It had sat awhile and needed some work. I polished her up and got fresh oil and gas in the motor and it has ran pretty well for an old carb motor... It started to run rough later that summer so I took it in to the repair guy.
They replaced the fuel pump, water pump and rebuilt all 3 carbs. New plugs and it ran great.
At the end of last year it started to run rough again and I didn't do much to it other than drain and replace the lower unit oil before storing it for winter.
This year its is running terrible and sputtering on top end bad... It will fire right up and idle just fine and will get on plane slower than normal but at WOT it only runs about 40mph and sputters bad... I think im down a cylinder or two... I also lost my tachometer??? Voltage regulator maybe? Im thinking a bad ignition coil or something in the timing... Im not 100% sure, but Im almost positive its not fuel related. I ran two full cans of sea foam through it at the end of the year last year and it made no difference.

I have 105-110psi compression on all cylinders.
I have good clean spark plugs. ( they ALL look good and light tan in color.)
I have spark on all 6 cylinders on the muffs in the driveway.
I have confirmed 100% open butterflies on the 3 carbs at WOT

Not sure how to test much past this.
I am very handy with a voltmeter as Im an HVAC service technician
Any help would greatly be appreciated!

[leonreno]

First thing you need to do is order a service manual from Mercury, don’t get an aftermarket, get an OEM manual from Mercury. I would vote Fuel first, then carbs, then electrical. Have you checked the fuel lines, they will degrade from the inside out. If they have never been replaced then that’s my first guess, second would be a carb that is clogged or a carb that maybe running rich.

try this first:
https://www.bbcboards.net/showthread.php?t=22490

[JOE54]

^^^^^ + agree also do an ohm test on the trigger and move the advance arm while doing it to eliminate wire breaking down in harness

[Racingfan]

I have a CDI book. I ohmed out my trigger. According to the book it says my resistance should be between 1100-1300ohms. My readings don't seem to change when advancing the arm.
But, my readings are as follows
1) 1130ohms
2) 1010ohms - low
3) 764 ohms considerably low...

Does this mean its defective? If so, I can replace it. Im not a marine mechanic. But I understand the operation. I don't have a DVA adapter but will buy one if needed. My marine mechanic is booked out 12 weeks right now...

[Racingfan]

The fuel lines are new as of 3 years ago. As well as the fuel pump and cleaned and tuned carbs... I know that it can be fuel. But im almost certain its ignition related...

[JOE54]

trigger is bad

[wbh1954]

... Do a Compression Check.

[EuropeanAM]

When you replace that trigger, there are critical steps that are required (measurement of the linkage, and after proper installation, a COMPLETE SYNC-N-LINK must be done).

Failure to follow these steps properly can result in catastrophic engine failure.

Also note: If the only thing you've done is change the gear lube and run seafoam through it, you're due for some maintenance. Plugs, fuel filter, water pump, etc.

Also... don't overlook the regulator situation. Check for any browned, blackened, burnt or discolored connectors (replace BOTH regulators and any damage connectors if these are noted).