low hour 2000 4.3 Mercruiser starting & running too rich to run...

Porschesolutions

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Jun 18, 2017
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49
Hi guys,
This is my first boat. I've built Porsche motors & race on occasion so I know EFI components & such but this old TBI is foreign to me.

I just bought a low-hour VIP Runabout with about 40-50hrs on it (per the prior owner), and for the most part the boat appears to be a time capsule. It was started for me and I remember it running VERY rich but as assured it was just still "warming up". The gas didn't smell and the owner and recently pumped out the oil & replaced it with a fresh 5qts. Once back home, I put in another 15g to fill the gas tank up with 87 octane, continued to start/run it here/there and it always felt/sounded like it was picking up cylinders as it warmed up over 2-3 minutes. Felt confident to take it to the lake for the first time on Saturday, where after plenty of opportunities to warm up (145-ish degrees on the gauge), it would run so rich it wouldn't even go up on plane and would lose cylinders due to fouling/running too rich. After a while of letting it "evaporate" & such (3-4 times of shutting it off & waiting for the plugs to dry), we headed back & it fouled while idling & wouldn't immediately re-start so a SeaDoo towed us back: my wife was not impressed :) The first time we shut the boat off & anchored/jumped into the water to relax while the plugs dried, we noticed quite a bit of gas soot all over the back of the boat that we had just cleaned: VERY rich.

We burned about 1/4 tank of gas idling around with about 1.5 hours of running time...yes, basically idling in-gear.

Here's what I've done so far:

1. Replaced plugs with the proper AC plugs: it had like-new NGK Platinum (un-gappable) plugs in it that referenced a GM LS1 motor, totally fouled. New plugs are at .045 gap.
2. Cap & rotor & wires look new, crappy how there are two sets of possible wire order numbers at each disty terminal that are not correct, but the disty cap is keyed so it only goes on one way. Verified TDC & the 1-6-5-4-3-2 firing order & spark plug wire routing.
3. Removed all the oil: it was heavily gas-fouled & black even though it should have been "fresh". it's fresh now...new filter too: 5 quarts 10w-40 to run until I solve this problem & then will change the oil again & go for the proper marine 25W-40.
4. Boat wont fully start now: I guess it's still getting way too much fuel and the proper spark plug gap being smaller is allowing for even easier plug fouling. I was hoping it was just old/bad plugs and a fresh tank of gas & an Italian tune-up would help fix this issue but it appears deeper than that.
5. there are a couple of un-connected wire ends near the carb that might have something to do with a possible electronic choke problem.

A friend of mine suggested I look at the butterflies/choke butterflies to see if they're stuck open or closed which could explain this; I'll do that tonight. I might pump out the gas & swap in some Berrymans B12 and see if I can get it to clean up. The sucky part is that we have family moving to Korean (via Military contract) in a week & wanted to entertain them this weekend: looking kinda iffy for that.

My motor is pretty easy to access for checking things...feel free to shoot me some questions.

No I do not have a manual (yet)
No I have not checked the fuel filter (not this cause yet agree it needs to be found/checked)
No I have not checked the air/water separator but again think this is more of a choke issue.

Thanks in advance for your suggestions. :)

Mark
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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welcome aboard

if you have a choke, you have a carburetor and not TBI

if you have a carb and its running that rich, most likely the carb is dirty and the needle is stuck, or the fuelpump died and the clear fuel pump vent hose from the fuel pump to the spark arrestor is full of fuel.

post your serial numbers

here is an on-line source for manuals http://boatinfo.no/lib/library.html
 

Porschesolutions

Seaman Apprentice
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Jun 18, 2017
Messages
49
It appears to be a carb but from 1996 on I've seen references to it being a TBI.

I'll post my SN's tonight & will try to find some info on the Library link you sent: saw that over the weekend but much easier to navigate on my bigger screens at work :) Thanks Scott.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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the 4.3 came in Carb, TBI and MPFI

since the boat only has 50 hours on it in the past 17 years, it sat alot. worst thing you can do for a boat.

my guess the crud in the carb is starting to solidify. pull the carb, soak it, clean all the passages, and put in a new seal kit. replace the float as well.

also, verify that the clear hose from the fuel pump to the spark arrestor isnt full of fuel. if it is, the fuel pump diaphragm is shot and the pump needs to be replaced.
 

Porschesolutions

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Last night I verified a slightly sticky choke, cleaned/adjusted it to no avail. Spark arrester looks new but was cleaned anyway.
Checked the in-carb filter: looked brand new.
Boat still wont fully start or run.
Tonight I'll first test & then disconnect the pump, replace the fuel filter, drain the carb via running it, fill the bowls with Barrymans & let it soak, remove/clean/re-seat idle mixture needle & adjust (out 1.25 turns from seated), will syphon out some gas from the tank's bottom to see if there's water/crud in it, will reconnect the fuel line & try starting it up again.
If all this doesn't work, then yes it's time to pull the carb & go through on the bench.

Oh motor SN is OL614688
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Last night I verified a slightly sticky choke, cleaned/adjusted it to no avail. Spark arrester looks new but was cleaned anyway.
Checked the in-carb filter: looked brand new.
Boat still wont fully start or run.
Tonight I'll first test & then disconnect the pump, replace the fuel filter, drain the carb via running it, fill the bowls with Barrymans & let it soak, remove/clean/re-seat idle mixture needle & adjust (out 1.25 turns from seated), will syphon out some gas from the tank's bottom to see if there's water/crud in it, will reconnect the fuel line & try starting it up again.
If all this doesn't work, then yes it's time to pull the carb & go through on the bench.

Oh motor SN is OL614688

you cant soak the crud out, you have to pull the carb apart, and in many cases, use compressed air to clean the passages. sometimes you need to use pin drills. its no harder than rebuilding a porsche 2.7 mechanical fuel injection system or a pair of 3-throat 40mm webbers

your fuel/water filter alone should tell you if you have water in your fuel.
 

Porschesolutions

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Yes, I feel you're right: time to rebuild the carb.
Last night I:
A. pulled the fuel line from the carb, disconnected the pump, ran the fuel out of the carb, blew in as much Berryman's as the carb would take given my angles of access, let it sit while I removed/cleaned the idle mixture needle & re-set it to 1.25 turns from seated.
B. Connected a fuel line to the hard fuel line & verified the pump: ran out about 2 gallons of gas in 3 minutes: plenty for this 4.3 I'd think, so pump is good, gas was clean & replaced the water/fuel filter while I was at it.
C. Set the idle screw & then re-connected & got the same boggy results. Since it's been 3 days, I pulled the spark plugs to clean them again: plugs 2-4-6 were wet & sooty as before. Plugs 1-3-5 were very dry, very clean & perhaps lean; so this tells me that since all 6 cylinders are sucking near-equally, I have one side of my carb flowing fuel & one basically not. Gonna pull the carb tonight & source a carb kit today during lunch. Thanks again, Mark
 

Porschesolutions

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https://youtu.be/JfmjQkHwUk4

Ok I rebuilt the carb & cleaned the spark plugs: I adjusted a few things but found no clogged ports. Upon start up last night, motor does the exact same thing: kicks off on 3 cylinders, picks up 4 and perhaps 5 as the idle quickly rises, so I throttle back to keep it from over-revving & then the motor coughs & dies. Sheez.
 

Porschesolutions

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4.3 2000 Mercruiser won't idle or stay running (video)

https://www.youtube.com/watch?v=JfmjQkHwUk4

2000 4.3 Mercruiser 2bl Mercarb carburetor, Thunderbolt V ignition system (2000 VIP 18.4' run-about)

Just rebuilt the carb (adjusted a few things but didn't find any clogged passages but the carb sat for 2 days with Berryman's in the bowl.
Have recently:
-Replaced fuel/water filter, verified good strong fuel flow & good quality fuel to the carb.
-checked for TDC (harmonic) with #1 matching what I saw online; verified 1-6-5-4-3-2 firing order, good wires, clean cap & rotor
-replace spark plugs with proper with .045 gap
-re-set idle mixture setting (1.25 turns), idle speed screw (2 turns), Float tab bent to be set at 10mm & 29mm as per rebuild instructions, choke at 2mm at WOT
-oil change & filter & serpentine belt.

As you see, it starts poorly, picks up a few cylinders as I pull back on throttle to not over-spin a cool motor, then it coughs & dies, routinely. Intake manifold was dry, though 1/2 the plugs were dark & sooty & the other half of the motor looked like the plugs were nearly dry (not enough fuel). :(

All the boat places are booked, trying to solve this myself...family fun-day planned this weekend
 

Bondo

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Just rebuilt the carb

Ayuh,..... Welcome Aboard,.... It appears that job was a failure,.....

Was the carb completely disassembled,..?? Completely,..??
Were all the passages poked with a soft wire, 'n blown out with compressed air,..??

The idle, 'n air screw settin's are just startin' points, not the final adjustments,....
Have ya tried readjustin' the air screws at idle,..??

Yer comment 'bout 1/2 the motor rich, 'n the other side lean makes me think 1/2 of the carb is plugged up somewhere,....

Btw,..... 1 thread per problem,... No need to start another thread like that,...

My answer doesn't reflect on the then unavailable backstory,....
 
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Porschesolutions

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Well I went back to the basics last night; drained the carb & then did a compression test; 0 in Cylinders 3 & 5, so the head will come off this weekend. Did the test 3x, all the other cylinders were near 150psi on a cold motor.
 

harleyman1975

Ensign
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May 12, 2003
Messages
959
Well now that is something different all together. hopefully it is something just sticking and not rusted or bent.
 

Rick Stephens

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Well I went back to the basics last night; drained the carb & then did a compression test; 0 in Cylinders 3 & 5, so the head will come off this weekend. Did the test 3x, all the other cylinders were near 150psi on a cold motor.

Indeed it is something different. Good catch. Look forward to hearing what you find.
 

Porschesolutions

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No Title

Indeed it is something different. Good catch. Look forward to hearing what you find.


Ok I pulled the valve cover to find 4-6 snapped valve springs,from rust. Dunno what caused the rust: water in the vent, condensate collecting in the valve cover, or what. Put air into each cylinder via the spark plug hole and each of the two cylinders will hold air if I pull up on the valves (no help from broken springs ya know), so the headgasket appears good. I'll replace all the broken valve springs & will do a new compression test to ensure these cylinders do hold air: if so, I'll enjoy the boat for the summer and pull the heads to do a full valve job this winter. Already lost a month on the water dicking with this boat. my take is that the valve springs snapped on the first rev of the motor, leaving us stranded out in the lake: where cylinders 2-4-6 were pulling all the carb's fuel to that side of the motor, making it too rich to run. Fun times....lots of theories.
 

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Rick Stephens

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IMHO, rust didn't break springs, crappy springs broke springs. Replace em all, go boating for the summer. Best news imaginable as long as they didn't beat the tops off the pistons.
 

Porschesolutions

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All done but boat wont start: not even close: thinking the firing order is off via a mis-installed disty. Amazing how little info there is on the basics of this motor: rotation, firing order, how to get it to TDC on the timing marks w/o cranking it a few dozen times, etc. :/
 

Porschesolutions

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Oh thanks! That is NOT what I found or currently have the wires routed- will pull the boat out of storage in three weeks and will try that. Mucho thanks Rick!!
 

Porschesolutions

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Ok finally retrieved my boat from Storage and rearranged the wires but still not even close to starting- gonna take a gym / Christmas lights break and then get back on finding TDC with #1 plug removed before I pull Disty and clock. I think it?s installed incorrectly. Ugh.
 
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