# Mercruiser carb problem?



## FERG 06 (Oct 6, 2006)

Had the boat out today and having a little trouble.
Mercruiser 3.0. Has always run great. Put 17gals of fuel in it to fill it up (was about half full).
Running out of the bay, water nice, pushed it to full throttle, no problem. Back her off a little, no prob. Trolled for a short time till the wind picked up, no prob.
Went to head back in and slowly throttled up to between 1500 & 2000 rpm's and it started surging. Back to idle in gear, no prob. Back up same rpm - surging. I could goose it from there and it would take off like normal.
Get up on plane, runs fine, pull the throttle back to that rpm range-surging.
Seems like the intermitate ports might be plugged up. Hope it's not a tank of bad gas. 
If I try some sea foam how long would I have to run it to see if it gets better (wasn't planning on running it till vacation in 3 wks). Hate to burn up a bunch of $4+ gals of fuel running around trying to clean it up for nothing. 
Checked the plugs 4-6 wks ago but nothing else. I'll check cap, rotor & fuel filter this week. Thinking of pulling the top of the carb off to see if anything looks cruddy. If it would take alot of fuel trying to clean it up I might as well tear it down and clean it up. 

Would it be possible to put seafoam straight in the fuel bowl vent to soak it or could that eat up the accel pump (not sure how strong that stuff is). Then I'd still have to take it out for a run.


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## roger23 (Jan 14, 2001)

check the tank vent line make sure it is clear..spiders plug them,also sometimes they sag and fuel or water settles in the low spot,,


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## roger23 (Jan 14, 2001)

If you tear the carb apart,check the float,some have foam floats in them and they start to absorb gas and get heavy,they seem ok ,but if you weigh a new one VS the old one to tell..they say alcohol in gas now eats the coating off of them???so they absorb gas


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## FERG 06 (Oct 6, 2006)

Vent line would be a huge pain to check. This is a cuddy cabin boat. Maybe I over filled it? Didn't see anything coming out the vent. and I did burn a bit of fuel coming out of Brest Bay so the level should have dropped down. 
Seems like it wouldn't be a fuel flow prob in the lines or pump as i've got no prob at higher rpm's and full throttle. Like I said it wil jump out of the water like normal.


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## roger23 (Jan 14, 2001)

May be a vacuum leak,I have seen the base gasket leak,I usually spray gum out around the base if it starts to stall you found the leak,does it have points and condenser if so points mat be out of adjuctment.condenser may break down


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## FERG 06 (Oct 6, 2006)

roger23 said:


> May be a vacuum leak,I have seen the base gasket leak,I usually spray gum out around the base if it starts to stall you found the leak,does it have points and condenser if so points mat be out of adjuctment.condenser may break down


Yeah it's got points which were in good shape/adjustment last year but I've put alot of miles on her since then.
I've got an electric ignition I pulled out of another boat that I was going to try to install before vaca. Looks like it's a must do now.
As far as a possible vac leak I'll check for that (done it on many old cars) but not sure what I'll find as when on the water, when in neutrel at the said rpm range it didn't seem to surge. Only with a load on it. Who no's maybe it will me some good signs when I mess with it.
Hoping I don't have to waste alot of time as i don't have much to begin with. My local fishing is pretty much over till after vacation.


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## FERG 06 (Oct 6, 2006)

Looks like I'm gonna have to replace the fuel pump. Got vapor and sludge/gum in the overflow line. (took pics but it's too much trouble to post 'em) Junk in the filter at the carb probably from the diapragm coming apart. Going to also pull the carb to see if anything got in there.
Plugs look like new but dist shaft is rusty cause the sponge is gone bye-bye. Looks like that elect. ign. is in order.
Lots of late nights ahead of me. Got three weeks till vacation.:woohoo1:


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## Priority1 (Feb 5, 2006)

I rebuilt my fuel pump. Some of the older ones can be rebuilt. Replace your fuel line also. The older ones are not alcohol compatible. The alcohol likely deteriorated the fuel pump. If yours has screws that hold it together, I can give you a site where you can get parts. It's about 1/2 the cost, and it took me less than a half hour on the bench.


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## FERG 06 (Oct 6, 2006)

Priority1 said:


> I rebuilt my fuel pump. Some of the older ones can be rebuilt. Replace your fuel line also. The older ones are not alcohol compatible. The alcohol likely deteriorated the fuel pump. If yours has screws that hold it together, I can give you a site where you can get parts. It's about 1/2 the cost, and it took me less than a half hour on the bench.


Thanks, I'll take a look at that. Found a new one online at a place I've bought before for $91, free shipping if I spend $100, which I will after getting some other stuff.


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## roger23 (Jan 14, 2001)

I don't know about a 3.0 but the ones I have replaced on 4.3 V6, 350"s & 454"s are the same as the car or truck ones except the black paint,,I never had any complain anyway or had to rework any


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## FERG 06 (Oct 6, 2006)

Priority1 said:


> I rebuilt my fuel pump. Some of the older ones can be rebuilt. Replace your fuel line also. The older ones are not alcohol compatible. The alcohol likely deteriorated the fuel pump. If yours has screws that hold it together, I can give you a site where you can get parts. It's about 1/2 the cost, and it took me less than a half hour on the bench.


Yeah, it's the old kind. Screws holding it together. What's that website?
This will take me back. I remember rebuilding them on cars in the 70's.


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## Priority1 (Feb 5, 2006)

http://www.then-now.com/The_Cellar/cellar.htm

Here's the link.


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## Priority1 (Feb 5, 2006)

roger23 said:


> I don't know about a 3.0 but the ones I have replaced on 4.3 V6, 350"s & 454"s are the same as the car or truck ones except the black paint,,I never had any complain anyway or had to rework any


They may look the same but the marine fuel pumps are CG approved. The marine ones have dual diaphragm or a sight tube that leads to the carb throat. If a mechanical pump fails on a car the fuel will leak on the ground. If an automobile fuel pump is used on a boat and it leaks, the fuel leaks into the enclose bilge, and you can be in a heap of trouble. Trust me on this one.


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## Damark Marine (Mar 26, 2008)

Priority1 said:


> They may look the same but the marine fuel pumps are CG approved. The marine ones have dual diaphragm or a sight tube that leads to the carb throat. If a mechanical pump fails on a car the fuel will leak on the ground. If an automobile fuel pump is used on a boat and it leaks, the fuel leaks into the enclose bilge, and you can be in a heap of trouble. Trust me on this one.


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## roger23 (Jan 14, 2001)

I never did a L4 ,maybe the newer ones are different ..the ones I have done were single fuel line to and from the fuel pump I will look tomorrow at a new one,I understand what you are talking about, I know all about the CG parts ,,I changed a started that was not CG approved, they found it on a inspection one engine had a marine starter the other did not.and the fire system was not properly installed


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## FERG 06 (Oct 6, 2006)

Priority1 said:


> They may look the same but the marine fuel pumps are CG approved. The marine ones have dual diaphragm or a sight tube that leads to the carb throat. If a mechanical pump fails on a car the fuel will leak on the ground. If an automobile fuel pump is used on a boat and it leaks, the fuel leaks into the enclose bilge, and you can be in a heap of trouble. Trust me on this one.


Yeah, I was thinking that too.


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## FERG 06 (Oct 6, 2006)

Installed the electric ignition, new fuel pump and line, pulled the carb and cleaned out the junk in the bowl and jets. Test ran and adjusted in the drive during the week then out to Belleville Lk for final testing.
Did final timing and adjusting of the carb on the water then gave 'er a good test run. She's running like new, starts quick, runs smoother when first started and is ready for my trip to the west side. 

Now if I can only catch some fish! :lol:


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## Priority1 (Feb 5, 2006)

FERG 06 said:


> Installed the electric ignition, new fuel pump and line, pulled the carb and cleaned out the junk in the bowl and jets. Test ran and adjusted in the drive during the week then out to Belleville Lk for final testing.
> Did final timing and adjusting of the carb on the water then gave 'er a good test run. She's running like new, starts quick, runs smoother when first started and is ready for my trip to the west side.
> 
> Now if I can only catch some fish! :lol:


WTG Ferg. GL on the Salmon Slammin.


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## roger23 (Jan 14, 2001)

thats a good feeling when you do all that work and everything works like new


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## FERG 06 (Oct 6, 2006)

roger23 said:


> thats a good feeling when you do all that work and everything works like new


That's why I tend to do the work myself.
Been wrenching for over 30 yrs now.


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