Merc 3.0 carb. issue

[Peels]

2004 merc 3.0

its a glastron 175..if that matters.

FINALLY got to be out on the water for more than 10 minutes!!! YAY all went well...just noticed:

It has a bit an "unhappy" rpm range. Low to mid...If i'm trying to cruise slow, it surges a bit....rpm fluctuates... not really hurting anything, just annoying. It jumps up and down 2-300 rpm. Also, same note...have to give it alot of throttle, then back off to get the speed up if If I'm trying to hit that low range... runs fine at speed

Is this something inherent to this model of engine? OR is it a carb/timing issue.

Only asking in the hope of shaving time...dont want it down too long this time of year I do well with carb work, so I'm not scared there...just nailing down the direction to go....

Oh, It also "Diesels" when you shut it down..but I'm betting that has more to do with 6 month old gas than anything else... so we'll see when I refill. Maybe get some 91.

thanks folks...

 

[nathan]

I would start with timing. how Hard is it to start?

 

[Fun Times]

Just curious if you have a mercarb or TKS (Turn Key start)?

When was the last full tune up? Timing, spark plugs, carb adjustment, etc, etc using OEM parts?

The 3.0's need to be adjusted precisely to avoid dieseling.

 

[Peels]

Just curious if you have a mercarb or TKS (Turn Key start)?

When was the last full tune up? Timing, spark plugs, carb adjustment, etc, etc using OEM parts?

The 3.0's need to be adjusted precisely to avoid dieseling.

TKS.. Id have to look into that.

First time boat owner, just purchased in fall. Other than having professionally winterized, and an impeller change by previous owner, I cannot be sure of the services.

I did spark plugs myself(NGK), and the fuel filter was changed during winterizing. (at least I paid for it)

Starts fine (when warm) slight delay on cold start. Idles OK, a smidge rough when cold.

Timing was something I thought of... I'll have a poke around.

thanks for the responses

 

[Fun Times]

2004 should have been a mercarb as TKS came out in 05 but how merc does things it could go either way. Hopefully you'll have the mercarb on there. Your engine serial number may help tell the story though.

TKS.. Id have to look into that.

Starts fine (when warm) slight delay on cold start. Idles OK, a smidge rough when cold.
Timing was something I thought of... I'll have a poke around. thanks for the responses

Fine tune adjustments should help especially with the dieseling but requires a lot of patience, testing and retesting after each adjustment is done to get it right. It's sometimes easier to do with the throttle cable disconnected to get it running just right, but reconnecting the throttle cable correctly is just as important to do so that you don't have to much or little preload on the throttle cable stud affecting your previous adjustments.

Also take note of the how the nut and washer is loose on the throttle cable/stud attached to the carburetor. The nut needs to back off one full turn so that washer will spin freely or the cable may hold the throttle open at different settings each time you move the throttle handle.

Do you have the Mercruiser service manual for it?

Thanks for the thanks Nathan.

 

[nathan]

thank you it is hard sometimes on forums to find someone with real knowledge!!

 

[john lamon]

Boat Tech would this motor have a knock sensor? Mine was doing just as he described with the surging and it ended up being the knock sensor was bad, it's a older EFI though.

 

[Fun Times]

Boat Tech would this motor have a knock sensor? Mine was doing just as he described with the surging and it ended up being the knock sensor was bad, it's a older EFI though.

Hey there John, No the mercruiser 3.0ltr's did not utilize the knock sensor system, even their latest 3.0L MPI EC (Emission Controlled) did not utilize the knock sensor system as well.

 

[john lamon]

Hey there John, No the mercruiser 3.0ltr's did not utilize the knock sensor system, even their latest 3.0L MPI EC (Emission Controlled) did not utilize the knock sensor system as well.

Lol, I read 3.0 merc at first and thought we were talking about a big 3.0 outboard, brain fart, haha...

 

[Fun Times]

Lol, I read 3.0 merc at first and thought we were talking about a big 3.0 outboard, brain fart, haha...

 

[Peels]

thank you it is hard sometimes on forums to find someone with real knowledge!!

next time weather permits, Ill play with it.

Looks like were gettin the ole shafteroo here in Iowa for the holiday weekend....as far as boating goes..

 

[Peels]

I didnt get a chance to look at this yet... its more of a "bother" than a show stopper. I can throttle quickly, and it goes pretty well. It's really if i try to run slow around 1800-2200 rpm...I can hear the intake...but no power, and the rpm's fluctuate...

IN my world(not always right) this seems like carburetion issues....not timing. But I'm going to mess with it anyways. wish me luck.

 

[Peels]

timing looks spot on.

accelerator pump? But rpm's bounce around during low throttle.....driving slow...hmmm.

It does it on muffs with no load too. I can hear it "gulp" for air right as I gas it, then hesitate. SO I back off and gas again, it goes...

Note: If it already at high rpm, and I goose the throttle, NO problems. hmm...

any other advice?

rebuild carb during winter i think, regardless. just trying to keep it running nice through the summer....as I can already feel the days dwindling....

river too high again.

 

[nathan]

pull the carb and check the gasket between the carb and intake. if it has any defects it can let air in. also on the accelerator pump make sure it is in the carb straight and there are on tears in the material. you will have to pull apart the carb to check it.

 

[Peels]

pull the carb and check the gasket between the carb and intake. if it has any defects it can let air in. also on the accelerator pump make sure it is in the carb straight and there are on tears in the material. you will have to pull apart the carb to check it.

will do.

I'm leaning toward accelerator pump. or some sort of blockage type of deal. Fuel filter is new...

Ive dealt with carbs before, but mostly small (ATV) engines. THis is a little different, but the concept is still the same.... air and fuel...conspiring to ruin my day. LOL

HAvent taken the merc carb out yet, I expect the same sort of fun

 

[Fun Times]

To try and make the repair job a little easier for you before you even get started with it, on your next adventure into the boat, Could you write down and post the engine serial number so we could try and find the correct engine parts catalog and maybe the correct service manual somewhere online for you to read through beforehand that is if you're in need of it.

 

[Peels]

thanks boat tech!

I wrote that down on a piece of paper last night...........














the piece of paper which is on my workbench AT HOME

LOL look for it later tonight

like I said, this problem isn't a show stopper. just an annoyance. So ill most likely wait til as late in the season as I can. so I don't miss out on on boating days. And, that way, I can relax a little, and not feel rushed...relax and get it done right. I have a tendency to lose parts LOL

Well Be ready for next year.

 

[Sean]

I know you checked the fuel filter...
but what about the pickup screen in the tank?

 

[Peels]

I know you checked the fuel filter...
but what about the pickup screen in the tank?

I did not check that. I would think with that, there would be more problems than just that 1000-2500 rpm range... but anythings possible. something else to look into.

thanks!

it runs flawlessly at 3000. which is good planing engine speed with the smaller prop on it. depending on how many people are in the boat.

and I forgot that notepad with the engine # on it it was a loooong (FUN) weekend.

 

[Peels]

There is a lot of info on the webs about this...Jeesh. Lol


Serial on motor is 0m688851.