Mercruiser 4.3L Carb, low idle, stalling *UPDATE*

[Scag]

*SEE UPDATE in thread below*

Hello! Noob here, trying to diagnose my idle problem. I just recently replaced a bad ignition lock assembly and now i'm onto fixing my idle problem. I am having difficulty starting the engine without giving it a little throttle. After I get it started, it seems to run o.k. with throttle, but if I move the throttle to neutral, it will slowly idle down to about 400 rpms, stay there maybe 5-10 seconds, and then eventually stall out. My initial thought was the change the fuel filter. This seemed to help very slightly, but ultimately, it still stalls out every time.

Heres what I have determined and what I know:

1. Problem started easter weekend (last week) out on the water
2. Have trouble starting, but engine seems to run fine when under throttle (ran great on the water)
3. When in neutral/idle, will stall out after 10 seconds or so.
4. When it does idle, its very weak...around 400 rpms (should be 650)
5. Only way to start it is with a little throttle added
6. I've changed the fuel filter - didnt do much
7. Also had temp guage go out last weekend - assume unrelated. Next to fix
8. no excessive smoke when stalling or anytime for that matter.
9. No abnormal noises, pops, etc.
10. No known history of this type of symptom. Engine has 108hrs.
11. Running 93 Octane

The engine is a carbed mercruiser 4.3 model year 01.

ANY help is much appreciated. Thanks!

 

[zbnutcase]

Re: Mercruiser 4.3L Carb, low idle, stalling =(

Re: Mercruiser 4.3L Carb, low idle, stalling =(

Any carbed engine needs throttle added to start;that is normal. Have the ignition timing checked and if ok just turn the idle speed up on the carb and go boating! 'nutcase

 

[havasuboatman]

Re: Mercruiser 4.3L Carb, low idle, stalling =(

Re: Mercruiser 4.3L Carb, low idle, stalling =(

When this problem started, did you have a lot of weight in the boat? People, gear, etc?

 

[Scag]

Re: Mercruiser 4.3L Carb, low idle, stalling =(

Re: Mercruiser 4.3L Carb, low idle, stalling =(

Any carbed engine needs throttle added to start;that is normal. Have the ignition timing checked and if ok just turn the idle speed up on the carb and go boating! 'nutcase

Well I didnt assume it was bad for the boat to add throttle, but up to this point, I usually didn't have to add throttle to start it. So I guess i'm wondering what has changed. How would I go about checking the timing? Is this something I can do myself? What tools are involved? What causes the engine to fall out of proper timing and what does this happen only at idle? I do not have a lot of experience working on engines so bare with me =)

When this problem started, did you have a lot of weight in the boat? People, gear, etc?

Yes actually, I had 7 people plus gear (boat is a 19 footer)....interested to hear what you are getting at with this question!

Does anyone see ANY possible relation to this problem and the engine temp gauge malfunction? I didn't think there was, but both symptoms happened on the same outing.

Thanks for the input guys!

 

[Scag]

Re: Mercruiser 4.3L Carb, low idle, stalling =(

Re: Mercruiser 4.3L Carb, low idle, stalling =(

I'm trying to put anything out there that may have caused something to go wrong; when I was out Easter weekend, we did go through some extremely shallow areas when we were navigating into a beach. Could this symptom be anyway related to sucking sand through the intake? Again, I wouldnt think so seeing as how the boat seemed to run fine the rest of the day, but this occurred shorty after launch....it was at the end of the day that the boat had problems. Just throwing it out there...as you can see...i'm grasping for a cause.

 

[havasuboatman]

Re: Mercruiser 4.3L Carb, low idle, stalling =(

Re: Mercruiser 4.3L Carb, low idle, stalling =(

When you load a boat down with weight, it naturally sits lower in the water.
Because of this there is more back pressure on the exhaust. The engine is having to work harder to push the water out of the drive and Y-pipe.
That is why the spec's for setting the idle on a boat say you are to set the idle "in the water, in gear, and under normal load."
Have you had the boat back in the water since this problem occured? If not, you may want to get it wet and see. Might find the problem is gone.

 

[Scag]

Re: Mercruiser 4.3L Carb, low idle, stalling =(

Re: Mercruiser 4.3L Carb, low idle, stalling =(

When you load a boat down with weight, it naturally sits lower in the water.
Because of this there is more back pressure on the exhaust. The engine is having to work harder to push the water out of the drive and Y-pipe.
That is why the spec's for setting the idle on a boat say you are to set the idle "in the water, in gear, and under normal load."
Have you had the boat back in the water since this problem occured? If not, you may want to get it wet and see. Might find the problem is gone.

Well I guess its worth a shot! Heres my question though...if the engine used to start and idle fine on the muffs, but doesn't now, wouldn't that indicate something has changed? For the bad I presume?

I am going to have to find some time to get the boat on the water!

 

[Scag]

Re: Mercruiser 4.3L Carb, low idle, stalling =(

Re: Mercruiser 4.3L Carb, low idle, stalling =(

I also wanted to ask again if anyone saw an relation to the temp guage outage and this problem or is it most likely sheer coincidence?

 

[Juniinc]

Re: Mercruiser 4.3L Carb, low idle, stalling =(

Re: Mercruiser 4.3L Carb, low idle, stalling =(

Don't think so,,,
Is your carb adjusted correctly(idle mixture/curb idle screws?).

 

[Scag]

Re: Mercruiser 4.3L Carb, low idle, stalling =(

Re: Mercruiser 4.3L Carb, low idle, stalling =(

Don't think so,,,
Is your carb adjusted correctly(idle mixture/curb idle screws?).

Funny you say that...i'm about to go home and try. A buddy of mine suggested the same thing. Ideally this would be done in water, but do you see any reason why I can't get it close on the muffs?

Thanks for the reply. I really appreciate it.

 

[Juniinc]

Re: Mercruiser 4.3L Carb, low idle, stalling =(

Re: Mercruiser 4.3L Carb, low idle, stalling =(

nope, I've gotten it pretty close on the muffs,,,
eventually final adjustment in the water.
adjust her at her operating temp.

Funny you say that...i'm about to go home and try. A buddy of mine suggested the same thing. Ideally this would be done in water, but do you see any reason why I can't get it close on the muffs?

Thanks for the reply. I really appreciate it.

 

[cr2k]

Re: Mercruiser 4.3L Carb, low idle, stalling =(

Re: Mercruiser 4.3L Carb, low idle, stalling =(

more back pressure in the water. I thought that's what the idle relief ports were for?

 

[PitchFork]

Re: Mercruiser 4.3L Carb, low idle, stalling =(

Re: Mercruiser 4.3L Carb, low idle, stalling =(

nope, U'll be fine on the muffs,,,
adjust her at her operating temp.

My manual states:
"Final Idle Speed and MixtureIMPORTANT: Boat must be in the water and engine
at normal operating temperature to accurately
check and adjust idle speed and mixture.
Carburetor should be set so that engine idles
smoothly within range given under ?Specifications,?
with boat in the water, engine at normal operating
temperature and drive unit in forward gear. To adjust
idle speed and mixture, proceed as follows:
IMPORTANT: DO NOT attempt to compensate for
other engine problems (incorrect ignition timing,
faulty ignition components, low compression,
vacuum leaks, etc.) with carburetor adjustments.
This will only cover the problem, which must be
corrected if engine is to achieve maximum fuel
economy and performance.
1. Connect an accurate shop tachometer to engine
2. If new or rebuilt carburetor has been installed,
turn idle mixture needle in (clockwise) until it
lightly contacts seat, then back out needle 1-1/4
turns. This will provide a sufficient setting to allow
starting engine.
3. Start engine and run at 1500 RPM until engine
reaches normal operating temperature.
! WARNING
DO NOT leave the helm unattended while performing
idle speed and mixture adjustments, following.
BE CAREFUL NOT TO ACCIDENTALLY
ACCELERATE ENGINE WHILE PERFORMING
ADJUSTMENTS.
4. With boat in open water, place remote control in
forward gear, idle position.
5. Disconnect throttle cable barrel from anchor
stud. Be sure not to lose spacer on anchor stud.
6. Adjust idle speed adjustment screw to obtain
550-600 RPM, in neutral gear.
7. With engine running at specified RPM, adjust idle
mixture needle as follows:
a. Turn idle mixture needle in (clockwise) until
the engine speed begins to drop due to lean
mixture.
b. Turn idle mixture screw out (counterclockwise)
until the speed begins to drop due to
rich mixture.
c. Turn screw in to a point between these two
extremes to obtain maximum engine smoothness
and RPM.
d. Readjust idle speed adjustment screw until
engine idles at 650-700 RPM in forward gear.
IMPORTANT: Refer to Section 2 - ?Removal and
Installation? for throttle cable installation and adjustmen"

 

[BRG25]

Re: Mercruiser 4.3L Carb, low idle, stalling =(

Re: Mercruiser 4.3L Carb, low idle, stalling =(

Clink on this link and download Service Manual Number 25. It has good troubleshooting information for you to follow.

http://forums.iboats.com/showthread.php?p=1693398#post 1693398

 

[Scag]

Re: Mercruiser 4.3L Carb, low idle, stalling =(

Re: Mercruiser 4.3L Carb, low idle, stalling =(

Well the rain kept me from tuning. I have to leave out of town tonight and wont be back till next friday. I really apprecaite the help. I'll be sure to update what happens...hopefully with some pics...

 

[havasuboatman]

Re: Mercruiser 4.3L Carb, low idle, stalling =(

Re: Mercruiser 4.3L Carb, low idle, stalling =(

more back pressure in the water. I thought that's what the idle relief ports were for?

They are still under water.

 

[Scag]

Update

Update

Well, I finally got back in town and was able to hop up in the boat to tinker around (i'm on the muffs at this point.) After starting the boat up and realizing the same results as earlier, I did the following:

I started by turning the idle adjustment screw (inwards/clockwise) 1 Full turn. RESULT: not much of a difference.

I did another full turn, noticed rpm's were a little higher at idle, but it still eventually died.

I did one more full turn (thats 3 turns total). And I got it to hold an idle at a hair under 600 rpms.

What I did notice that is still different from before was 1.) I have to give the motor throttle to start it, 2.) I have to rev it probably 5-8 times before it will idle, otherwise the rpms drop to quick and it wants to stall, so I just rev it a little up to about 1500-1800 rpms before it dies and then finally the rpms drop slow enough down to 600 that it wont die.

I wanted to adjust it further to get it perfect at 650, but it got dark and I didnt want to push my luck. I also figure that I really need to wait till I get it on the water to fine tune it. I can't wait to get it on the lake!

Does 3 turns seem like a lot? The spring that is compressed when the screw is turned seems kind of corroded. It seems very stiff...is this how it should be?

Thanks for all the help guys!!! I'll keep you updated!