1999 Mercury 225 Carb 3.0 won't rev past 3500-4000RPM

[DamianJP]

Motor is in great shape and has looks to have been maintained.

7-21-13 water/fuel sep filter

Primer stays hards.

new champ plugs at .035 and inline filter above top carb.

Seems to have had 3 CDM (Coils) changed , 2 on one side 1 on other.

Motor is turn key idles perfect

Start accelerating to around 2000 rpm and start to hear miss or something and then and quick stumble sometimes, then onward to 3800rpm-4000rpm it sound rough but starts to go but the motor won't go past that rpm range (3800-4000). Throttle is all the way down and the boat won't plane.

Anything 2000 rpm approx. and under and she's golden.

At first the stumble made me think fuel deliv but the rpm "brick wall" , seems to be spark now. But I will check both.


Checklist and Questions


Check fuel lines and check valves on return fuel lines.

Check crank position sensor for .040in +- .020in (How can I check if the CPS is good at all ?? )

Check TPS (TPI)
IDLE 0.950 ? 0.050 VOLTS
WOT 3.80 ? 0.25 VOLTS

Any way to check the stator with just a multimeter? DVA is home.

Does this motor have a rev limiter or a "Limp Mode"?


What do you guys think it could be? Where should I start my search?



Thanks,
DamianJP

 

[DamianJP]

Re: 1999 Mercury 225 Carb 3.0 won't rev past 3500-4000RPM

Bump

 

[DamianJP]

Re: 1999 Mercury 225 Carb 3.0 won't rev past 3500-4000RPM

They state Champion QL77CC at .035
But CDI website troubleshooter says .035 for EFI .040 for carbs, they are at .040

Symptoms recap:
Perfect idle
Miss around 1000-2000
After 2000 want to go but still alittle off.
Then rev limit/struggle at 4000 like its being held back, spark wise.


Got it !!

Started the checklist...

Compression: 110-115 all well within %10

Wanted to lighten my list of process of eliminations right off the bat so I swapped out crank and throttle posistion sensors with known good ones and set em up. Symptoms persist. (Thanks to Brother in law's 99' EFI)

I started to think stator high speed wirings , but don't have my DVA, meter , manuals,tools....ect.

So had two cheap harbor freight in line spark checkers. Wanted to check if 1 or more cylinders were failing and at what RPM. So started at the top cylinders. Found that when we re created the symptom the starboard middle cylinder was have ZERO spark.

Swapped middle and top CDM's and so some strange reason now both CDM's are working. So I swapped em' back around to re create symptoms and still %100 spark.

Bad connection or ground to middle CDM is the culprit.

Took her out and she sang , right on plane. Friend was happy as hell and to be honest I think I was just as happy to learn more, turn a wrench and to have a easy fix.

Hope it helps someone else.
-DamianJP