Mercruiser 5.0L Carb issue

I had couple of questions and maybe you guru's out there can assist with my issue. I have an Mecruiser 5.0L Carb, Serial # 0W311065. I've replaced spark plug, fuel/water separator. Boat been sitting since Dec of 2010. Ran the motor on muffs this pass weekend and the motor started up idle perfect, I let it run for about 20 minutes on the muff and motor sounded good. Took it out the next day on the water, started it up fine, left the dock doing about 40mph and the then motor splutter and shutsoff. Tried to restart it but wont start. Waited couple of minutes and would still not start. So i pushed in the lever and gave it some gas and it would start but when i put it back into neutral motor shutsoff. So i took off the Flame Arrestor and adjust the idle screw. My buddy push the lever forward and i can see fuel squirting into the carb. Place the lever back started the motor up in neutral and the motor stays on. Left the motor running about 5min idle was a bit high but didnt want to lower just incase it would shutoff again. Need to get back to the docks so i put the motor in gear and it didnt shutoff, when i accelerated i can hear backfire and splutter like the motor was going to die, so i dropped the lever to lower the speed to get me going atleast. I couldnt go wot or the motor would splutter and shutoff. I'm guessing and reading the the forums here, leaning toward bad fuel or dirty carb. I've bought some Seafoam and going to pour some into the fuel tank let it run and then clean out the carb with seafoam/carb cleaner. Any ideas would be greatly aprreciated.

Thanks

Re: Mercruiser 5.0L Carb issue

I'm guessing and reading the the forums here, leaning toward bad fuel or dirty carb.

Click to expand...

Ayuh,.... Welcome Aboard,...

Pull the filter filter, 'n inspect it's contents,..

Run it on a remote tank,...
How old is the gas in the tank now,..??

Re: Mercruiser 5.0L Carb issue

Thanks, ..I've been doing a lot of reading on this forum and alot of things I've learned. The gas is pretty old, which had stabilzer. what i didn't think was when I went out, I've pumped in new gas to the existing gas, didnt realize it would cause anything. I'll try pulling the fuel filter and see what it in it. I was going to do a clean of the carb this weekend, taking out the fuel lines and cleaning it and cleaning the screen. Thing i noticed was when i looked down the carb, it was pretty black, dont know if that's normal or not. Will seafoam help this out? Will bad gas or clogg carb cause the backfiring? spluttering? engine dying?

Thanks again..

Re: Mercruiser 5.0L Carb issue

Will bad gas or clogg carb cause the backfiring? spluttering? engine dying?

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Yes...

Re: Mercruiser 5.0L Carb issue

Thanks Bond-o for the quick response.. I will tackle this job this weekend and hopefully doesnt rain. and post back.

Re: Mercruiser 5.0L Carb issue

My 8 year old gas finally lost enough Octane & lighter fuel parts to be hard to START. Ran ok @ WOT. I filled the 6 gallon tank with 1/2 can of Seafoam & high test. Hand starts came back easily. Just a tap of the starter fires it now. Check the plug color. The plug if black is probably arcing but NOT at the gap. That will give a easy start but terrible higher speeds. Change the plug to.

Re: Mercruiser 5.0L Carb issue

I've already changed spark plug. Well after doing the seafoam stuff, ran it on muff for about 2 hours testing and idling. Revin to 2k rpm +, it started and ran like a champ. Yesterday took it out to the water to test, started it up fine, let it warm up at the docks. Then about 15 minute of idle, wanted to test it before i left the dock and sure enough boat bogged and died. Started back up, let it idle for another good 15min. Rev pass 2000 rpm and everything was fine, but when put back in neutral it died. I'm at a complete loss. So got home, unplug the fuel line from the carb and plugged a hose to the fuel line and let it run some fuel into a bottle. Didnt see any debris or anything in there. So I took the whole carb apart. I'm at a point to rebuilding the carb. When i opened up the carb, i saw some red gunk in the carb but not enought to cause anythign i hope. I'm really at a complete loss. Why on muff it works like a champ and on the water it dies. I was gonna mess with the idle mixture screw but it has a plastic cover over the screw. So i'm not sure if it's made to adjust. After rebuilding, What are some thoughts? Any suggestion would be great. Damn i sure miss going out fishing.

Thanks Fellows.

Re: Mercruiser 5.0L Carb issue

Thanks bubba, took the carb apart and everything looks pretty easy. I've bought a manual and reading on this forum really made me understand much more about these engine. Will the carb rebuild kit come with everything i need? or do I have to buy additional stuff?

Re: Mercruiser 5.0L Carb issue

Hey all,

Finally finished rebuilding the carb. Followed all the spec, measuring the float, etc. put on the boat today, Put my baby on muffs and fired her away, took awhile to start her up but finally it started up. For some reason it wont stay idle. Anythign below 1k rpm motor shutsoff. I've tried adjusting the idle screw and ilde mixture screw, got her down to 650-700 rpm at idle but then happens again dies. What I'm seeing with the flame off, fuel constantly going in, not from the jet but looks like the enrichment. It's kinda hard to start the boat after it dies. I would have to put the throttle 1 once or twice in order to fire her backup.

Any suggestions or ideas would really help at this point.

Thanks all

Re: Mercruiser 5.0L Carb issue

You were given some really good suggestions already. Should have run on a remote tank. Then... a total rebuild of a carb that may have build up and deposits in the small passages requires sitting for a bit submerged in Chem-dip. Thats why, as bubba told you, most rebuilds never work out properly. Now your problems seems worse not better and you still dont know if your original problem was the on board tank or the carb...
Sorry to be a Kill Joy...

Re: Mercruiser 5.0L Carb issue

Yah, I was hoping that rebuilding the carb would help and clean out the deposit within the carb. Geez bad mistake. Is there anything within the TKS system that will make the boat not idle? When i turn up the idle to about 1200-1500 rpm motor stays running, i can see that fuel is coming out from the venturi cluster. but when i turned down the idle motor just dies. With the motor shutoff, pushed the lever down, i can see fuel squirt from the jets. Another thing i changed was the cap and rotor. I've checked and I'm getting good spark. Did i do something wrong within the Carb, that would cause this? maybe float is off?

For the remote tank, I was on low gas already and pumpled out as much as i can and put in new fuel with seafoam and still didnt resolve it that's why I went for the carb rebuild. So when i took off the carb looked down the fuel bowl, there were red/brown deposit in there.

Re: Mercruiser 5.0L Carb issue

slixxster said:

Yah, I was hoping that rebuilding the carb would help and clean out the deposit within the carb. Geez bad mistake. Is there anything within the TKS system that will make the boat not idle? When i turn up the idle to about 1200-1500 rpm motor stays running, i can see that fuel is coming out from the venturi cluster. but when i turned down the idle motor just dies. With the motor shutoff, pushed the lever down, i can see fuel squirt from the jets. Another thing i changed was the cap and rotor. I've checked and I'm getting good spark. Did i do something wrong within the Carb, that would cause this? maybe float is off?

For the remote tank, I was on low gas already and pumpled out as much as i can and put in new fuel with seafoam and still didnt resolve it that's why I went for the carb rebuild. So when i took off the carb looked down the fuel bowl, there were red/brown deposit in there.

Click to expand...

Sounds like the deposits you saw in the bottom of the carb bowl could be plugging the idle circuit?? Did you find anything in the filter/separator? Water or debris? I don't know anything specific to the TKS, never had one. Sounds like it is stumbling and dieing when trying to transition from the idle circuit to the main circuit.
Hopefully one of the Mercruiser mechanics will chime in.
Good luck!

Re: Mercruiser 5.0L Carb issue

Possibility 4
"What I'm seeing with the flame off, fuel constantly going in, not from the jet but looks like the enrichment".
Check fuel pump, I had same thing too. Went through tank clean, fresh gas, filters, rebuilt carb.
Turns out PO blanked safety overspill pipe from pump. The diaphram was torn and rather than send gas to carb and flood engine out (as yours is) it was pumping gas straight into oil pan. NOT good Sounds like you have same symptom with excess fuel going in.
Please dont try to save $$$ by fitting a pump from an auto instead of a marine pump.

Re: Mercruiser 5.0L Carb issue

Loss of one of the check balls during disassembly of the carb will cause fuel overflow. An improperly installed inlet needle will flood the carb. Incorrect float height will cause a rich condition. An incorrectly installed float will cause a rich condition. Improper adjustments will cause a rich condition. Incorrect choke adjustment will cause a rich condition. A black coating on the carburetor throat is indicative of a rich condition. Hard starting in the presence of excess fuel is an indication of a rich condition. So look for causes of a rich condition. And when you rebuild a carb, every passage must be squeaky clean. Cleaning the float bowl does not constitute a carb rebuild.

Re: Mercruiser 5.0L Carb issue

And when you rebuild a carb, every passage must be squeaky clean. Cleaning the float bowl does not constitute a carb rebuild.)
- I've taken the whole carb apart and dipped it in chem dip for 1 day, Gasket was pretty hard to remove, but was able to buy gasket removal and using a razor to pull all of it off, then sprayed at least 4 bottle of carb cleaner let it dry and then used an air compressor to spray everything else out.

Incorrect choke adjustment will cause a rich condition.-
My motor doesnt have a choke adjustment, It's a Mercruiser 5.0 TKS- from reading it's a electric choke.

Loss of one of the check balls during disassembly of the carb will cause fuel overflow-
Only have 1 check ball and pulled it apart again and still in same location. Check ball goes in between the venturi, with a spring and a T clip to hold it together.

An improperly installed inlet needle will flood the carb. Incorrect float height will cause a rich condition. An incorrectly installed float will cause a rich condition.
- checked the needle and only not much to check. (Was thinking of putting the needle without the spring?)-Let me know if that will help it.? double check the float from gasket to dot measurement is on the dot at 9mm. with the top carb flipped over hanging the float down, measurement is 24mm. per Manual, I even tried going 22mm. Not much difference.


Possibility 4
"What I'm seeing with the flame off, fuel constantly going in, not from the jet but looks like the enrichment".
Check fuel pump, I had same thing too. Went through tank clean, fresh gas, filters, rebuilt carb.
Turns out PO blanked safety overspill pipe from pump. The diaphram was torn and rather than send gas to carb and flood engine out (as yours is) it was pumping gas straight into oil pan. NOT good Sounds like you have same symptom with excess fuel going in.
Please dont try to save $$$ by fitting a pump from an auto instead of a marine pump.

-I'm not sure what your talking about here, but my electric fuel looks to be good, check and psi is around 5. Checked and no gas is in my oil. Pulled the Fuel Filter/Water Separator and no debris or water. so just went ahead and replaced it with a new one.

When i turn the idle screw to 1k rpm, i do see constant fuel coming out of venturi into the carb. When i push the accelarator, i see 2 good spray of fuel. I'm not too sure how this TKS system really works since i dont have a choke to adjust. When the boat idle's at 1k or above it's running fine. When i drop the idle down it slowly dies. Then when I try to restart the motor, it wont start until i pump some fuel into the carb. Will the enrichment module(TKS) be the affect? check spark plug and doesnt look like I'm running rich, looks like it's burning fine. So i dont think I'm flooding. With the engine running, pulled the tube going to the valve cover and motor dies. With the motor running, cover the top of the carb with my hands and motor slowly dies.

If anyone knows how this TKS system works or how to troubleshoot, please shine some light on me.

Thanks again for all the assistance.

Re: Mercruiser 5.0L Carb issue

TKS is a standard carburettor with an electrically activated enrichment valve to make starting easier, nothing more.

All the same rules for a carburettor clean (I would stop using the word 'rebuild' as all you're doing is cleaning and checking the adjustments), soak in carb-cleaner, use clean dry compressed air, blow through the passages in BOTH directions, use new gaskets and check everything twice. The compressed air needs to be at a pressure of about 100psi or more. Any less than that may not blow hard enough to move any dirt away.

Which manual are you using? If it's not the genuine Merc one, trash-can it! Get a genuine one -> http://www.4shared.com/document/SNqPsoNI/Service_Manual_41.html

It sounds very much like you have still got dirt in the passages, specifically the idle and progression hole. You may now also have a leaky needle and seat. Did you replace them on the original clean out?

Another possibility is the engine is by-passing and too much is getting into the carb. Try pulling the PCV valve out of the rocker cover and see what happens...

Chris........

Re: Mercruiser 5.0L Carb issue

I've replaced everything that came with the OEM Mercury Rebuild Carb KIT, and yes that is the same manual I followed. Manual 41. I guess it's not rebuild but bought the rebuild kit from Mercury. Replace, spring & checkball, Acc pump, needle/seat, even had to cut the old idle mixture cover to remove it to place the new idle/air mixture screw. I was off a bit on the float weight and bought a new one. When i pull the PCV tube of the rocker cover, engine stalls and cuts off.

Unless this kit i bought is bad? bad needle/seat?

Re: Mercruiser 5.0L Carb issue

You need to pull the whole valve out, or pull the hose and plug it....

Turn the carb upside down. You should NOT be able to blow low pressure air into the fuel inlet. If you can, you have a leaky n&s...

Re: Mercruiser 5.0L Carb issue

Slixxster,
I alerted achris to your carb problems...
You should follow his advice and report back as accurately as possible to him, If anyone can help you thru this it would be him.

Re: Mercruiser 5.0L Carb issue

thanks joe and chris, I really appreicate your guys help. Everyone has been great on this forum.

You need to pull the whole valve out, or pull the hose and plug it.... (So your talking about the PCV tube? if so plug it up?)

Turn the carb upside down. You should NOT be able to blow low pressure air into the fuel inlet. If you can, you have a leaky n&s... -(So do i have to take the whole carb out? if so do i need to put a new gasket?