'08 3.0L MerCruiser dies at low RPM. Carb, bad fuel, both?

[zealer]

Hello everybody,

I have recently acquired a small bow rider equipped with a 2bbl carburated 3.0L MerCruiser engine and Alpha One out drive (everything is from 2008). The motor is exhibiting some odd behavior and I was hoping someone may have a few pointers for me. Here's the problem.

I was out in the boat the other day (for the first time) and it was running fine for most of the day. When I dropped it into the water, from a cold start it would only start on fast idle and needed to warm up before I could drop it to low idle (otherwise it would stall). This I think is pretty normal behavior for a carb'd engine, at least in all of my carb'd motor experience (family had a boat several years back, it did the same - I come from the fuel injection world). So moving on. Once the motor did warm up, I could drop it to idle and it would do alright, it was a bit rough, but worked. With slight adjustment I figure I can get it to even out. Anyways, still not the problem I am after (but could be related).

As the day progressed, the engine became less likely to idle, eventually where it would only run at fast idle, and then would only run at higher throttle than fast idle. It would only start at or past fast idle, and I would have to feather the throttle to keep it running (out of gear). It would rev up fine, but coming back down it would always start to die. It got to the point where if the engine wasn't at 2500+ rpm, it didn't want to run. Luckily (well sort of), this behavior only started to show when I was headed back to the dock (which made docking some serious fun! No low speed control). Dropping the boat into or out of gear and the engine would immediately die off, unless serious throttle was applied, which unfortunately, is not good for the drivetrain.

After doing some reading and applying my limited knowledge of carbs, I was thinking it could be one or all of these following reasons:

1) idle circuits being plugged, or some sort of obstruction in carb
2) bad fuel (this is the tank the boat was winterized with)
3) fuel tank is not venting (this I will check very shortly, I just read in the manual to leave the fuel flap open if this is suspected and to see what happens)

I have carb cleaner and Seafoam. I put Seafoam in the tank and was just out spraying the carb cleaner. Oddly enough, occasionally the carb cleaner increased RPM, and sometimes it would decrease RPM (lowering RPM is indicated by the label). I'm hoping it is just debris or varnish and the Seafoam/cleaner will do the trick... but, I really haven't a clue. I suppose I will order a manual tonight, but would like to at least diagnose the problem by the end of the weekend.

Does anyone have any insight?
Engine serial:1A023075

 

[Maclin]

Re: '08 3.0L MerCruiser dies at low RPM. Carb, bad fuel, both?

It sounds like the carb is leaking fuel into the intake and flooding the engine. Pull the spark plugs and look at them. If they are all black and sooty, or wet looking then there is too much fuel getting in. Also check the oil via the dipstick, check for a fuel odor from the oil.

Also pull the flame arrestor (with engine off!) right after it dies at idle and see if lots of fuel vapor is coming up through the carb throat, even listen for sizzling.

 

[Silvertip]

Re: '08 3.0L MerCruiser dies at low RPM. Carb, bad fuel, both?

Spraying seafoam or any other cleaning agent down the throat of a carburetor does nothing to clean the insides of the carb which is where the issue likely is (if it is a carb issue at all). SeaFoam burns so spraying it down the carb would increase rpm if the engine was not getting enough fuel, or tend to stall it if it was getting normal fuel amount. How much you added can affect how the engine responds. Check the fuel for water. Is the choke working properly. Is it adjusted correctly. When was the engine last tuned. Idle mixture and idle speed properly set? And add some fresh fuel.

 

[zealer]

Re: '08 3.0L MerCruiser dies at low RPM. Carb, bad fuel, both?

Seafoam went in the tank (heard good things about it so why not). Spark plugs look normal, they are grey. Fuel vapor does come up when it dies. I was doing some more trouble shooting today. Couldn't get the engine to stay running below 3000 rpm and even then, it isn't particularly smooth. It wanders +- 200rpm. I reset the idle speed screw as per manual 26 instructions (backed out, just touching cam then 2 full turns), however I cannot access the idle mixture screw. According to the manual, it is a sealed screw.

This engine has an electric choke, and again according to the manual there should be scribe marks so that I can verify it is working correctly and adjust if needed. However, I see no such marks.

I would like to check the timing, but as is cannot get the engine running smoothly or anywhere close to idle.
Really at a loss as to what to do next. I suppose running on an isolated fuel supply is the next step.

This is the manual I have been referring too: http://www.maxumownersclub.com/forum/site_files/manuals/mercruiser/26.pdf

 

[airshot]

Re: '08 3.0L MerCruiser dies at low RPM. Carb, bad fuel, both?

Sounds like it is time for a thorough carb overhaul and cleaning, the kit comes with instructions for setting up all components on the carb including choke. Over the years the carb has become gummed up and with constant tinkering to make it work it has gotten way out
of adjustment. Time to give it a complete overhaul.

Airshot

 

[lukeb83]

Re: '08 3.0L MerCruiser dies at low RPM. Carb, bad fuel, both?

time to rebuild the carb. my boat was just having this same issue. qucksilver makes a great kit you can get on amazon for about 80 bucks.
i would check the filter as well.

 

[zealer]

Re: '08 3.0L MerCruiser dies at low RPM. Carb, bad fuel, both?

Yes unfortunately I think that is what it is going to come down to. I plan on doing a few more checks tomorrow, and then on Monday make a few calls.

Why do carburetors need to be rebuilt so often? The boat is only 5 years old - I find that an awfully short period to need a rebuild (I understand it could be days old as opposed to decades, but when it's plugged its plugged. I guess I just feel that in this day and age there would b greater pr?vention methods) . I suppose I am just more accustomed to the fuel injection automotive world.
Regarding rebuilding the carb, I am at a crossroads as to rebuild myself or bring it in. I am mechanically adept but am hesitant based on my nearly non existant carb knowledge. Although I suppose it is a great way to learn...

Seaman, I will look into the quicksilver kit. I also saw one from mikes carburetor parts for $40, any thoughts on him?

 

[Hoosmatroos]

Re: '08 3.0L MerCruiser dies at low RPM. Carb, bad fuel, both?

When you buy the kit and read the manual you should be good. It is not difficult as you keep working systematically. Make some pictures when you disassemble things. After all new gaskets and cleaning, replace your fuel/water separation filter and run for the first time with an isolated fuel source.

 

[aerobat]

Re: '08 3.0L MerCruiser dies at low RPM. Carb, bad fuel, both?

i doubt you have to rebuild a 5 year old carb.

i have a volvo penta 3.0 , but it should be basicly the same

-there is a metal fuel line from the pump to the carb, at its end screwed to the carb it has somekind of a small filter element- look into this , is it free or clogged ?
-look at the flame arrestor, is it clean ? test run without flame arrestor and look if its the same
-remove the carb, is the gasket to the manifold ok or does it suck false air ?
-make sure your fuel pump is working correctly .

cheers !

 

[dubs283]

Re: '08 3.0L MerCruiser dies at low RPM. Carb, bad fuel, both?

Why do carburetors need to be rebuilt so often? The boat is only 5 years old - I find that an awfully short period to need a rebuild (I understand it could be days old as opposed to decades, but when it's plugged its plugged. I guess I just feel that in this day and age there would b greater pr?vention methods)... I also saw one from mikes carburetor parts for $40, any thoughts on him?

depends on what you are using for fuels, additives, fuel stabilizer, etc... - keep in mind, most boats don't get used for a period of 6 months or so, not to mention all the time sitting in your driveway or at your dock, in the marina...

the best prevention methods are practiced by the boat operator, if you don't have a clue - go to a local reputable repair shop, not just a boat dealer - talk to someone who works on boats from all years - dealers who sell new boats basically only work on new boats, warranty work, swapping out parts and not troubleshooting, etc...

as far as a carb kit, you get what you pay for, quicksilver or sierra will have parts designed for marine carb use, who knows what "mike" uses

 

[palace]

Re: '08 3.0L MerCruiser dies at low RPM. Carb, bad fuel, both?

check out Mikes Carburetor parts is you have resevervations about doing the rebuild yourself. He has some good youtube videos. He knows carbs Marine and Automotive.

Yes unfortunately I think that is what it is going to come down to. I plan on doing a few more checks tomorrow, and then on Monday make a few calls.

Why do carburetors need to be rebuilt so often? The boat is only 5 years old - I find that an awfully short period to need a rebuild (I understand it could be days old as opposed to decades, but when it's plugged its plugged. I guess I just feel that in this day and age there would b greater pr?vention methods) . I suppose I am just more accustomed to the fuel injection automotive world.
Regarding rebuilding the carb, I am at a crossroads as to rebuild myself or bring it in. I am mechanically adept but am hesitant based on my nearly non existant carb knowledge. Although I suppose it is a great way to learn...

Seaman, I will look into the quicksilver kit. I also saw one from mikes carburetor parts for $40, any thoughts on him?

 

[HT32BSX115]

Re: '08 3.0L MerCruiser dies at low RPM. Carb, bad fuel, both?

I have carb cleaner and Seafoam. I put Seafoam in the tank and was just out spraying the carb cleaner. Oddly enough, occasionally the carb cleaner increased RPM, and sometimes it would decrease RPM (lowering RPM is indicated by the label). I'm hoping it is just debris or varnish and the Seafoam/cleaner will do the trick... but, I really haven't a clue. I suppose I will order a manual tonight, but would like to at least diagnose the problem by the end of the weekend.

Does anyone have any insight?
Engine serial:1A023075

Howdy,


No. Carbs do not have to be rebuilt frequently. (My last boat went 39 years without a carb rebuild)

Fuel system problems are most frequently the result of fuel contamination. Either water in the tank or in the fuel or other contaminants.

You should start at the tank and inspect the fuel pick-up, anti-siphon check valve, fuel filter (if installed and if not, INSTALL one), pump, and lastly, the carb.

If you need to rebuild the carb, you can get a kit at Napa, or other place. It's not hard to rebuild one.

Oddly enough, occasionally the carb cleaner increased RPM, and sometimes it would decrease RPM

Of course it did! The engine burns it like gasoline........and if you spray too much you richen the mixture (and foul the plugs!)

Forget the "Snake-Oil" (seafoam etc), there is NO "mechanic in a can" that will fix fuel system problems. You're just wasting time and money on that stuff.....

Fix the fuel system.

Regards,


Rick

 

[lukeb83]

Re: '08 3.0L MerCruiser dies at low RPM. Carb, bad fuel, both?

ive heard many good things about mikes carbs. carbs dont have to be rebuilt that frequently. mine went 27 years! the ethanol that they are adding to the gas loves to gum up over the winter if u do not drain the carb at the end of the season. doing this and using stabil when u winterize will reduce this problem come spring. i learned the hard way too! good luck.

 

[airshot]

Re: '08 3.0L MerCruiser dies at low RPM. Carb, bad fuel, both?

As stated in other posts" carbs should not have to be rebuilt in only 5 years" is a true statement IF and only IF they were properly stored and proper fuel aditives were used. Yes there will always be that one individual that went 20 yrs and did nothing and never had a problem, but in the real world maintainence is everything. Those who take extra care in fuel system maintainence will probably not have issues so.....how well did the previous owner maintain the fuel system?? One never knows, so if proper mainttainence was not done then that is the reason for requiring a rebuild. Next thing is how good is the fuel you purchase?? One never knows for sure especially when buying at really discounted fuel prices. I have purchased fuel from reputable sources and have gotten water and other crud in my fuel requiring changing of all filters and draining the tank and starting over. As the boat is new to you a good rebuild should be in order then start from there with proper fuel system maintainence program.

Airshot

 

[zealer]

Re: '08 3.0L MerCruiser dies at low RPM. Carb, bad fuel, both?

Thanks for the advice everyone. Much appreciated. I did some more troubleshooting today - here are the updates.

I inspected & cleaned the ignition components - nothing out of the ordinary there.
Next up I checked the fuel filter at the carb end. Oddly enough, it had what looked to be sand grains in it, but it was no where near clogged. Cleaned it and put back in. The sand part sort of baffles me though... I wonder how it got in the tank.
Fuel pump is working correctly as well.

I am wondering about the quality of the gas in the tank - in particular, how it fared over the winter. I am wondering if after running it for the first time in the water, it gummed up the carb (boat ran fine for first half of day, when coming back to dock for lunch in town it showed some idle probs). I will rebuild the carb, drain the gas tank and start afresh.

This is the kit I am looking at: Mercarb Carburetor Kit That kit does not include a float. I suppose I should get one as well, correct?
I'll check the local stores as well but I suspect their prices will be nowhere near the above.

 

[lukeb83]

Re: '08 3.0L MerCruiser dies at low RPM. Carb, bad fuel, both?

if you are wondering about the fuel in the tank draining and cleaning it would be a good idea. if its full of crud u could redo your whole fuel system and just suck up more crap from the tank. while you are at it inspect and clean the fuel pickup inside the tank. also, if you can find fuel with no ethanol fill up there (gas stations near launches usually carry it). best of luck again. i had this same headache last season and it was a tank full of crud and a filthy pick up (the last thing i checked).

 

[HT32BSX115]

Re: '08 3.0L MerCruiser dies at low RPM. Carb, bad fuel, both?

I am wondering about the quality of the gas in the tank - in particular, how it fared over the winter. I am wondering if after running it for the first time in the water, it gummed up the carb (boat ran fine for first half of day, when coming back to dock for lunch in town it showed some idle probs). I will rebuild the carb, drain the gas tank and start afresh.

Probably not. If you're worried about it, just fill the tank with fresh fuel. I have run 2 year old gasoline with no problems.

I usually just leave my tank at 1/4 or less at the end of the season and fill it up when I go to use it in the Spring/Summer. I never use it but if that bothers you, put some STABIL or other fuel "stabilizing" snake oil in it at winterization.

 

[zealer]

Re: '08 3.0L MerCruiser dies at low RPM. Carb, bad fuel, both?

I have never had problems storing fuel either. I usually drop some stabil in it and am worry free. Maybe I am being paranoid about this boat...
I'm going to bring the carb in to my local auto parts store tomorrow and see if they can get me a kit. I don't really want to wait for an internet mail order to come in, nor do I want to pay the shipping (shipping across the border is a killer).

 

[zealer]

Re: '08 3.0L MerCruiser dies at low RPM. Carb, bad fuel, both?

Brief update:
Drained fuel tank just to check - no issues with fuel. Put fuel back into my truck

It is definitely the carb. Local auto place is getting me a kit for tomorrow. Hoping I can everything back together and buttoned up in time for the weekend. My uncle has a friend (apparently a magician) that is going to help me with the rebuild. Will post back with results.
In anycase, I am using service manual #26. Does anyone have one that is more up to date?
In the carb breakdown of manual 26, it still shows the carb having a traditional choke. I also want to make sure that the specs listed in 26 are also used for the current carb I have, where all screws are sealed.

 

[Hoosmatroos]

Re: '08 3.0L MerCruiser dies at low RPM. Carb, bad fuel, both?

#26 is what you need. Not sure what you mean by a "traditional choke"