5.0 mercruiser 0M361530 carb

[Regal628311]

Hello fellow boaters, need some help. Throwing the kitchen sink at this pig and still isn’t right. A few weeks ago noticed a sluggish performance concern with my boat. I purchased it 8 months ago and ran fine until then. Recently had tubers and couldn’t plane. So I started with some maintenance; cap, rotor, sensor, coil, plugs, wires, fuel water, used remote fuel tank, eliminated anti syphon, new fuel pump, oil/filter change… still having same concern. Barely planes with me alone in boat. Odd thing is it seems to be heat related, after cold soak it will not act up for maybe 20 minutes but then go to plane and bam no power.. debating looking at icm or rebuilding carb.. can anything else be cutting fuel or spark? Gauges show fine on dash when issue occurs 40-60 oil pressure and 175 water temp

 

[QBhoy]

Have a look at the auto choke on the carb. Or if it’s a TKS…at the enrichment mechanism

 

[alldodge]

SN shows Merc 2 BBL
Have you replaced the filter (item 4) inside the carb?
https://www.mercruiserparts.com/bam/subassembly/31837/2697/90

 

[QBhoy]

Good call from AD above there. Just had another wee thought there too. How’s the alternator, battery and associated? Is there a good charge evident ? If you were lacking this…your boat would run well for as long as there is enough power to fire the ignition system. Then when there isn’t…you’d get issues. Is it possible your battery is recovering enough just to run for a wee while.

 

[ROY WILLIAMS]

so the engine runs great 20 min ,,, then the engine drops the power ?,,
could be the engine runs correct heat then the ignition components breaks down..ICM ..

 

[Regal628311]

Have a look at the auto choke on the carb. Or if it’s a TKS…at the enrichment mechanism

I have not looked at it, would you visually see the choke flap closed?

 

[Regal628311]

Yes

so the engine runs great 20 min ,,, then the engine drops the power ?,,
could be the engine runs correct heat then the ignition components breaks down..ICM ..

that’s what’s happening.. is there a good way to test icm without throwing 700 bucks at the wall?

 

[QBhoy]

I have not looked at it, would you visually see the choke flap closed?

Yeah. Or partly…or enough to have an effect. Take the flame arrestor off when she’s undoubtedly warmed up and have a look.

 

[Regal628311]

Good call from AD above there. Just had another wee thought there too. How’s the alternator, battery and associated? Is there a good charge evident ? If you were lacking this…your boat would run well for as long as there is enough power to fire the ignition system. Then when there isn’t…you’d get issues. Is it possible your battery is recovering enough just to run for a wee while.

Battery is fairly new like 6 months old but even new the gauge read low on dash.. like 11.5 but never had any issues cranking or starting

 

[QBhoy]

Battery is fairly new like 6 months old but even new the gauge read low on dash.. like 11.5 but never had any issues cranking or starting

I’d say that you could still have such an issue even with a presumed new and healthy battery. If your alternator isn’t doing what it’s meant to. Worth a look. See what it’s putting out when running.

 

[Regal628311]

SN shows Merc 2 BBL
Have you replaced the filter (item 4) inside the carb?
https://www.mercruiserparts.com/bam/subassembly/31837/2697/90

Good point! I will check and replace. Adding to my checklist

 

[Regal628311]

Yeah. Or partly…or enough to have an effect. Take the flame arrestor off when she’s undoubtedly warmed up and have a look.

Thanks I’ll do that as well. Anything else that would kill spark or fuel? Sensor?

 

[Regal628311]

I’d say that you could still have such an issue even with a presumed new and healthy battery. If your alternator isn’t doing what it’s meant to. Worth a look. See what it’s putting out when running.

Thanks I’ll add this to my list. I’m sure the gauge isn’t accurate but I’ll check alternator output and maybe another battery

 

[Regal628311]

Yes

that’s what’s happening.. is there a good way to test icm without throwing 700 bucks at the wall?

Anyone got the manual?

 

[ROY WILLIAMS]

Battery is fairly new like 6 months old but even new the gauge read low on dash.. like 11.5 but never had any issues cranking or starting

the boat wiring is a smaller gauge wire from the battery to the ignition key.
typically 11.5DC on the dash voltmeter panel....then the engine starts and the voltage meter is around 14 DC..

 

[ROY WILLIAMS]

Yes

that’s what’s happening.. is there a good way to test icm without throwing 700 bucks at the wall?

I know the boat ICM is the semiconductors and the engine creates a high temp around the ICM ...then the engine runs down .the semi-connectors in today world is a lot of $$$..

 

[Regal628311]

Ok guys finally got around to checking out a few things.

-charging system output is 14v alternator and at battery
- checked screen at carb light debri so I cleaned and reinstalled
- checked for any intake leaks with carb spray and cannot find any
- choke is not bogging it down
-9v only out of icm red white wire to distributor?? Anyone know spec I’d assume this motor uses 12v or 5v only

Wish I had a icm laying around to toss on this.. anything else in the carb that would cause a low power after running 20 minutes?

 

[alldodge]

Should be 12V or more at the + side of the coil (purple wire)

 

[Regal628311]

Good call from AD above there. Just had another wee thought there too. How’s the alternator, battery and associated? Is there a good charge evident ? If you were lacking this…your boat would run well for as long as there is enough power to fire the ignition system. Then when there isn’t…you’d get issues. Is it possible your battery is recovering enough just to run for a wee while.

Should be 12V or more at the + side of the coil (purple wire)

This was the wire out of the ICM to the distributor sensor. Should that be 12v? I’ll check coil voltage next time I’m there any other electrical tests

 

[alldodge]

Out of the distributor will vary while the motor is running because there is a make/break going on at RPM from the sensor. May show up as 9V or other