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1989 Mercruiser 4.3L - fuel related problems

J

Joey White

Member
Since I have been trying to get my boat (1989 EBKO Monte Carlo) engine (Mercruiser 4.3l v6) to run I can't seem to not find problems, most of them I feel like are just because I don't know much about these GM marine motors. There is carburetor issues that I will hopefully be able to figure out, and one thing that I feel might be attributing to that is my fuel pump. So when I got this boat it came with an electric in-line fuel pump which I would imagine was not stock, since then I bought a 4-7 psi inline fuel pump for some testing with the engine, but the carburetor keeps flooding after usually 15-30 secs of just the pump running, not sure if this makes a difference but when it floods it comes out the venturis. So thinking that maybe I have to much fuel pressure I got a fuel pressure regulator which I make the pressure set to 5 at most, same problem. I was thinking that maybe I should just go with the stock fuel pump, but I couldn't see where it connects to the block. The first image is a spot on the intake manifold that I'm not sure what purpose it serves, at first I thought maybe the fuel pump goes there, but it doesn't look like it either. The second image, from what I could find, on the right side of the block is where the fuel pump is suppose to be mounted to the block, but there appears to be not bolt holes to mount it to. I've even lately been having electrical issues with this engine. So any help would greatly be appreciated to help get my project going in the right direction.

https://i.imgur.com/MhxdY3G.png
https://i.imgur.com/1w2ehOh.jpg
 
Most V6 GM Mercruiser marine engines do NOT have mechanical fuel pumps only electric and the one that came with the engine if inline with the fuel lines was the correct/Original OEM (if not replaced)

1988-1992 shows mechanical fuel pump

92 and newer had electric.

Your engine may not be original POST SERIAL NUMBER if you have it

If 5 psi is causing flooding most likely you needle inside the carb is stuck open. Which means a carb rebuild may be needed.


Link is to this web site showing the OEM electric design

http://www.marineengine.com/parts/m...14107-thru-0f000877/fuel-pump-and-fuel-filter
 
Where might the engine serial number be located? I know it is a good engine with 180 in each cylinder so it is possible it isn't the original one. Also I have rebuilt the carb twice with two new kits. I'm not sure how it is still flooding, I'm guessing I need to keep adjusting the float height, even though I thought it was very spot on.
 
It most likely would not be the float height adjustment that would allow flooding as long as it is close to the specified height.

When you had the carb apart, did you blow into the fuel inlet with the needle seated by lightly pressing down on the float to see if it was in fact seated and no air was coming through?

It is either needle to seat or over pressure.

Note: a basic rule of thumb for a float height is when top is upside down and float is hanging to set the height, LEVEL is always safe if you are unsure of the specific measurement...

Of course follow the actual height adjustment if you have it.
 
I don't think I tried blowing into it last time I set the height, but I have other times before when it has done the same thing. Also a good thing I should probably mention is that currently I am using the solid needle instead of the spring, I had been doing a lot of previous attempts with the spring needle and my best at not flooding as much has come from the solid needle.
 
Down by the starter almost to the end of the block casting, If it is an original Merc engine then there should be a small metal tag riveted to the block with the serial number.

If you look good and cant find it it may not be an original OEM but a refurbished newer block with Mechanical fuel pump delete,
 
Well I can not confirm it isn't stock, but it is missing the tag. The cover for the carburetor that has the engine specs also has the engine serial number which is linked to a 89, but it is possible that cover was just to the old motor.
 
Regardless of the year of the block, 99% of all v6 and now most V8's have the same electric fuel pump set up. In the late 90's they did away with mechanical pumps.

As long as you are 100% sure you are not exceeding 6-8 psi and only at 4-5 psi then the needle/float should hold.

As far as the Needle spring or no spring I would have to review why the change. I forget

Is this a Mercarb or rochester two barrel?

Mercarb has ONE air/fuel adjustment screw
 
Joey White said:
Well I can not confirm it isn't stock, but it is missing the tag. The cover for the carburetor that has the engine specs also has the engine serial number which is linked to a 89, but it is possible that cover was just to the old motor.
Click to expand...

If no tag then it is not the original block. It may be refurbished. either the original or a different one
 
Referring back to my first post, I put an image of the intake manifold and circled a weird port on the left of where the carburetor would be, so far no one I know has any clue what that could go to, since I have nothing connected to it.
 
That image look to me to be a EGR port or something like that. There should be a block off plate to cover it if not get one and gasket it or goop it up good

Here is the manuals float settings.

As far as spring vs solid, it is either to solve possible flooding

carb.png
 
Just to confirm, if I leave the electric pump on even with 5psi without the engine running for like 15-30 secs the carburetor should not flood. Only reason I ask this is because I don't want to be testing the carburetor on the engine anymore since I don't like flooding the engine.
 
Do you have a compressor? If so try hooking ait to fuel line and set at 6 psi to see if it leaks...

Image below shows the intake question.


2925-0910997-omc-cobra-43l-stern-drive-intake-manifold-2bbl.jpeg
 
Joey White said:
Just to confirm, if I leave the electric pump on even with 5psi without the engine running for like 15-30 secs the carburetor should not flood. Only reason I ask this is because I don't want to be testing the carburetor on the engine anymore since I don't like flooding the engine.
Click to expand...
Yes the electric pump will be running the entire time the engine is running. If you have 5 psi and still flooding then needle seat or float is the culprit. If you haven’t replaced the float this may be the issue they can get waterlogged with gas . Id get a new needle and seat even if you just replaced it.
 
I cannot assist you in testing the carb from my keboard.

You will have to be a bit creative to diagnose the issue.

You have the basics now you need to figure away to apply pressure to fuel inlet without gas, hopefully air.....even if you use a bicycle tire pump with a gauge on it....


The blow test with top of carb off of carb and upside down causing float to seat should be good enough...........you can certainly blow higher than 5 psi...

If not we may need to reach out to Ricardo...........He was a big blow hard......
 
Dieter said:
Yes the electric pump will be running the entire time the engine is running. If you have 5 psi and still flooding then needle seat or float is the culprit. If you haven’t replaced the float this may be the issue they can get waterlogged with gas . Id get a new needle and seat even if you just replaced it.
Click to expand...

I have seen some seats that have a very small but sharp circular bur left from machining the part. I have had to use something round/tapered to smooth it over so the needle would seat good and tight. Something a Phillips head end but smooth, no grooves

if done very lightly it will make a very small chamfer on the hole the needle fits in... very carefully!
 
Okay I will look into the carburetor once more, I have tried using my compressor before but I am a bit worried that I will be forcing too much pressure into the carb since the adjustment on it isn't that precise. So I'll go with the old fashion way and just blow into it. Hopefully I can get a better outcome then I have had in the past.
 
Okay, I might be figuring out somewhat of a problem. I completely don't remember what it is called, but there is that cylinder thing that screws in that hold in the needle and seat, when putting that in I'm not sure I put the right washer under it, even though it would seem that a washer isn't much, it completely screws up the float. I'm thinking there are two main different washers to use that comes in the kit. One being a red one and another being just a normal silver one. If I'm not mistaken the red one is actually for the power valve in the bottom of the bowl. But one concern of mine is that the silver washer doesn't perfectly sit around the cylinder thing, and appears it might be slightly leaking. Also I know with the old mikuni carburetors I use to rebuild they said always buy the real factory rebuild kits, no off-brand ones, so maybe I should look into getting a better kit since mine was defiantly in the off-brand section, if mercarbs are the same way. I really just don't want to buy a third one since I already bought two.
 
Joey White said:
Okay, I might be figuring out somewhat of a problem. I completely don't remember what it is called, but there is that cylinder thing that screws in that hold in the needle and seat, when putting that in I'm not sure I put the right washer under it, even though it would seem that a washer isn't much, it completely screws up the float. I'm thinking there are two main different washers to use that comes in the kit. One being a red one and another being just a normal silver one. If I'm not mistaken the red one is actually for the power valve in the bottom of the bowl. But one concern of mine is that the silver washer doesn't perfectly sit around the cylinder thing, and appears it might be slightly leaking. Also I know with the old mikuni carburetors I use to rebuild they said always buy the real factory rebuild kits, no off-brand ones, so maybe I should look into getting a better kit since mine was defiantly in the off-brand section, if mercarbs are the same way. I really just don't want to buy a third one since I already bought two.
Click to expand...
That is the seat part of the needle and seat. The washer is what seals the seat to the carb airhorn or top in laymans terms. If the wrong washer was used etc the seat wont make a seal to the airhorn and fuel will leak past it. Hard to tell from here what is proper for your carb. Mikes carb shop has some videos on its website detailing mercarb rebuilding. If you are saying it didnt match up when installing it thats a problem.

https://www.carburetor-parts.com/Mercarb-Carburetor-Kit--PK112_p_3483.html

by off brand whose did you buy? Mercruiser doesn’t make their own carb kits, as long as it was from a reputable supplier using quality parts its likely similar quality. If its a cheapo off amazon you may have issues. Ive had good luck with parts from mikes and from our host here at marine engine.
 
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What I mean by off-brand was a cheap like $11 kit off amazon. But it seems to be the same as on Mike's Carbs website It was just the video I watched on rebuild a carb was extremely old and I believe he skipped over the part of installing the seat. I'll look into some videos on that website to see if I can find out what washer I need to use.
 
The intake manifold pictures show a mounting for a non electric automatic choke. This is used on older models. That port goes down into an exhaust chamber in order to collect heat for the choke tube which carries hot air to a bimetal spring which operates the choke.
You have to use the correct washer/seal on that float valve seat......or you will have exactly the problems your experiencing.
 
Joey White said:
What I mean by off-brand was a cheap like $11 kit off amazon. But it seems to be the same as on Mike's Carbs website It was just the video I watched on rebuild a carb was extremely old and I believe he skipped over the part of installing the seat. I'll look into some videos on that website to see if I can find out what washer I need to use.
Click to expand...

Worse case, Use the old washer, To bad you dont live close, I have boxes of left over spare carb rebuild kits parts...........

Good find by the way!!

Sounds as if you have some background. I have actually spoken with Mike of Mike carbs.........He sell great parts!

I have used off brand carb kits---------hence the needle seat needing a bit of rework..........I did not purchase, customer did.


I have actually seen where the person who did a rebuild on a carb, screwed the seat in crooked and not all the way. I had to remove, chase threads with a tap, Clean well and re install (with washer) correctly. Made a huge difference.............lol
 
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Joey White said:
What I mean by off-brand was a cheap like $11 kit off amazon. But it seems to be the same as on Mike's Carbs website It was just the video I watched on rebuild a carb was extremely old and I believe he skipped over the part of installing the seat. I'll look into some videos on that website to see if I can find out what washer I need to use.
Click to expand...
That was just going through the kit do some looking around i think he has two videos rebuilding the mercarb.
 
Last night I just was testing the needle and seat, so I put the top of the carburetor upside-down, turned the pump on, and there is no leaks. I even left it overnight pressurized with some fuel like that and when I came out in the morning to it, it still had fuel pressure. But it always ends up flooding when I put the two half's back together, so basically when I can't see what is happening. First time I put the half's together, it flooded, float was to spec on all the heights, so I adjusted the float level way more then it says on the sheet. Then for once it didn't flood, held it for a good 30s then I emptied the bowl to make sure... And it flooded again... so either I'm doing something really wrong, or this carburetor is really just junk. I would just buy a new carb to solve my problems, but that's expensive and I have a limited budget of not spending money if I have to.
 
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