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Hello, and question about timing

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nkyrental

New member
First post, so hello to everyone. I have a 2003 Mercruiser 4.3L with carburetor. Each season I do all the fluid and filter changes, then do a test start with ears. Started fine, as usual. Got to the lake and the boat had good initial hole shot, but would not get above 3,000 rpm or 30 mph. It would then start bogging down and there was some unusual noise from the engine. At first I thought maybe it slipped the prop, but took it off and inspected. I am now thinking the timing was off. Has anyone experienced this type of behavior with the timing being off? The other thought I had was a clog in the fuel system, but that would not explain the noise from the engine bay.
 
1 First what temps were you seeing?

2 either getting hot, not getting fuel or water in fuel or not winterized properly and you are experiencing water in the engine. Pull spark plugs and see if water is present in any of the cylinders.

3 Possible coupler issue at back of engine (this is what drives the outdrive drive shaft) but that does not seem to be the cause yet.

The timing does not just change on its own. It could be a failed timing control module but I would not go there yet.

to many other things to check for first
 
Temp is at 130 and stable when heated up. Stays in a heated garage at at least 50 degrees all winter. The person who did the repairs just told me that he did adjust the timing slightly lean to stop the run-on that this engine is notorious for when you shut it off hot. I asked if he used the timing light, and he said no, he just moved it a fraction of an inch like he always does. I am wondering if he didn't tighten the nut enough and it moved during the drive down, 2 hours on the interstate. I will check the bolt tonight and see, then check the actual timing numbers. I checked the dip tube and the out-drive oil and no evidence of water at the lake. He also put in new plugs; I wonder if improper gap could cause this much problem?
 
Very important information you left out of your first post...............................

Well as far as I know he was wrong.

I am unaware of V6 carbed engines "running on"............so that is suspect.

also 130 degrees is too low.....to the best of my understanding the V6 of that year should have a 160 degree thermostat. That would mean you should be at ~ 170 nominal degrees.

So there is a good chance your gauge or sender is faulty or the wrong thermostat.

Some may say the 140 degree is better to use so even if you were using that one you should be running around 150 -160 degrees.

Also Idle speed should be ~ 650 rpm at idle in gear in the water under load


see attached. from Manual # 25

Also timing procedure
 
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We hit a log a few years ago and had the lower unit rebuilt. From that point on, the temperature has shown lower,usually right around the 120 on the gauge, sometimes just a tick over. Hasn't had a new thermostat since probably 2010. It definitely has run-on. If you go full out across the lake, then turn it off, it will sput and sputter until you gas it up with the throttle. Tried all sorts of stuff; letting it idle for a bit, turning on the blower, lifting the cover, the only thing that seemed to help was a slight leaning of the timing, they did this the first year we had it at the dealer when it was under warranty. By the middle of summer it would start sputtering again. Odd. Will be interesting to see what the numbers actually are with a timing light. RPM is around 900 without a load, adjusted in the driveway with ears on.
 
First off your temp is wrong no matter what. That being said you could be running hot and not even know it!! Maybe the noise was the noise of an over heating engine and the hose clamps creaking and rubber boots melting........

900 rpm is way to high for a mercruiser alpha one outdrive.

That is most likely the cause of you "run on" if nothing else. The engine idle rpm is set to 650 for a couple of reasons, 1. so not to damage the drive gears when shifting. 2. so the engine shuts off.

Many carbed engines when the idle rpm is to high will "run on"..............Boat or auto.

As far as the temp reading,
One thing that happens is the sending unit looses ground and the temp gauge will only reach around 110-120 degrees. Mine was like that for a while. My cause it was a stuck thermostat.
My friends boat was also reading ~ 120......his was the wrong base gasket on his design thermostat housing in which the sender was installed into, it did not have the correct gasket thus no ground for the sending unit.

The threaded section of the sending unit is ground.

It looks like the sender on your engine is screwed into the intake manifold either at the front of engine or rear.

So maybe tighten the sender to see if you re-establish a good ground or run a ground wire from battery neg to the sender body and see if gauge shows correct temp.
 
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Chris is this the tech bulletin?


Engine ‘Dieseling’ or ‘Running-On’
Models
MCM 4 Cylinder, V6 and V8 with Carburetors.
Situation
Under certain conditions, carbureted engines may ‘run-on’ when the ignition key is turned off. Normally, it
will take a combination of several of the following conditions to make the engine ‘run on’. These conditions
include but are not limited to:
1. Type and formulation of gasoline available in the area.
2. Type of boat and its engine compartment ventilation system.
3. Outside air, inside engine compartment air and engine coolant temperatures.
4. How quickly the engine is shut off after running at cruising or higher RPMs.
5. How the boat and engine are operated.
6. Engine idle rpm set too high.
7. Wrong heat range spark plugs or spark plugs with deposits on them.
8. Deposits in combustion chamber.
Carbureted engines, unlike EFI, do not shut off the fuel supply to the engine when the ignition key is turned
off. As the engine is coasting to a stop, air is still flowing through the carburetor into the manifold. This air
flow can still draw fuel from the carburetor, through the intake manifold and into the combustion chamber.
A hot spot in the combustion chamber will cause this fuel/air mixture to burn. The engine now ‘diesels’ or
‘runs
on’ although the ignition system is not firing. EFI engines do not have this problem because the injec-
tors do not inject fuel once the ignition key is turned off.

Suggestion to Minimize ‘Run On’
Items number 1 ,2 and 3 can correct or reduce most of these ‘run on’ problems. Letting any engine idle a
minute or
two before shutting it off is desirable. This helps the engine to normalize at idle rpm before being
shut down.
1. Be sure engine idle mixture, idle rpm and ignition timing are correct. On 4 cylinder and V6 or V8 engines
with Thunderbolt IV ignition, setting idle rpm as low as possible can help stop ‘run on’.
2. Adjust throttle cable barrel so that the carburetor’s throttle lever returns against the idle speed stop
screw every time the remote control throttle lever is returned to neutral, idle.
3. Idle engine 1 to 1-1/2 minutes before turning key off after running at cruise or higher engine rpm.
4. Try a different brand of regular fuel or try some premium fuel.
5. Increase idle mixture by 1/8 turn ‘richer’.
6. Go to next colder heat range spark plugs.
7. V6 and V8 only: Install a 140 F(60 C) thermostat.

17 JULY 1999

Available Colder Spark Plugs
Original Spark Plugs in the Engine:
Short Reach
Spark PlugAC-MR43T
Long Reach Spark PlugAC-MR43LTS
Replacement Colder Spark Plugs:
Short ReachSpark Plug AC-MR41T
Long Reach Spark PlugAC-None NGK-None NGK-TR6
Champion-RV12YC
OR
Champion-RV91MC
Champion-RS9YC
 
kghost said:
Chris is this the tech bulletin?


Engine ‘Dieseling’ or ‘Running-On’
Models
MCM 4 Cylinder, V6 and V8 with Carburetors.
Situation
Under certain conditions, carbureted engines may ‘run-on’ when the ignition key is turned off. Normally, it
will take a combination of several of the following conditions to make the engine ‘run on’. These conditions
include but are not limited to:
1. Type and formulation of gasoline available in the area.
2. Type of boat and its engine compartment ventilation system.
3. Outside air, inside engine compartment air and engine coolant temperatures.
4. How quickly the engine is shut off after running at cruising or higher RPMs.
5. How the boat and engine are operated.
6. Engine idle rpm set too high.
7. Wrong heat range spark plugs or spark plugs with deposits on them.
8. Deposits in combustion chamber.
Carbureted engines, unlike EFI, do not shut off the fuel supply to the engine when the ignition key is turned
off. As the engine is coasting to a stop, air is still flowing through the carburetor into the manifold. This air
flow can still draw fuel from the carburetor, through the intake manifold and into the combustion chamber.
A hot spot in the combustion chamber will cause this fuel/air mixture to burn. The engine now ‘diesels’ or
‘runs
on’ although the ignition system is not firing. EFI engines do not have this problem because the injec-
tors do not inject fuel once the ignition key is turned off.

Suggestion to Minimize ‘Run On’
Items number 1 ,2 and 3 can correct or reduce most of these ‘run on’ problems. Letting any engine idle a
minute or
two before shutting it off is desirable. This helps the engine to normalize at idle rpm before being
shut down.
1. Be sure engine idle mixture, idle rpm and ignition timing are correct. On 4 cylinder and V6 or V8 engines
with Thunderbolt IV ignition, setting idle rpm as low as possible can help stop ‘run on’.
2. Adjust throttle cable barrel so that the carburetor’s throttle lever returns against the idle speed stop
screw every time the remote control throttle lever is returned to neutral, idle.
3. Idle engine 1 to 1-1/2 minutes before turning key off after running at cruise or higher engine rpm.
4. Try a different brand of regular fuel or try some premium fuel.
5. Increase idle mixture by 1/8 turn ‘richer’.
6. Go to next colder heat range spark plugs.
7. V6 and V8 only: Install a 140 F(60 C) thermostat.

17 JULY 1999

Available Colder Spark Plugs
Original Spark Plugs in the Engine:
Short Reach
Spark PlugAC-MR43T
Long Reach Spark PlugAC-MR43LTS
Replacement Colder Spark Plugs:
Short ReachSpark Plug AC-MR41T
Long Reach Spark PlugAC-None NGK-None NGK-TR6
Champion-RV12YC
OR
Champion-RV91MC
Champion-RS9YC
Click to expand...
That would be it. Attached a PDF on my last post.

I fatten them up and lower the rpm just a tad. Usually does the trick here in NJ.
 
..................................
nkyrental said:
I have a 2003 Mercruiser 4.3L with carburetor. ............................... Got to the lake and the boat had good initial hole shot, but would not get above 3,000 rpm or 30 mph. It would then start bogging down and there was some unusual noise from the engine. ................................ I am now thinking the timing was off. Has anyone experienced this type of behavior with the timing being off?
OK..... let's assume that the ignition advance was excessive. In other words...... far too advanced from where the Factory wants it to be for any given RPM!
..... first, you may want to know that your 4.3L GM pistons are very prone to Detonation.
..... poor octane rated fuel and high cylinder temperatures perpetuate Detonation.
..... excessive ignition advance may perpetuate Detonation.
..... Detonation perpetuates high cylinder temperatures.
..... Detonation that has not YET caused any piston damage, will indeed prevent an engine from performing well..... such as bogging down!
Click to expand...

nkyrental said:
.................... The person who did the repairs just told me that he did adjust the timing slightly lean to stop the run-on that this engine is notorious for when you shut it off hot.
I too do not know what "slightly lean timing" would mean or indicate!

I asked if he used the timing light, and he said no, he just moved it a fraction of an inch "like he always does".
DO NOT allow this person to work on your Marine Engine in the future! He could cause you some very expensive repairs!

I am wondering if he didn't tighten the nut enough and it moved during the drive down, 2 hours on the interstate. I will check the bolt tonight and see, then check the actual timing numbers. I checked the dip tube and the out-drive oil and no evidence of water at the lake. He also put in new plugs; I wonder if improper gap could cause this much problem?
Spark plug gap is normally predicated by the output voltage. With a High Energy output system, the gap can be increased some.
Keep the gap where it should be for YOUR ignition system!
Click to expand...

nkyrental said:
..................... It definitely has run-on. If you go full out across the lake, then turn it off, it will sput and sputter until you gas it up with the throttle. Tried all sorts of stuff; letting it idle for a bit, turning on the blower, lifting the cover, the only thing that seemed to help was a slight leaning of the timing, they did this the first year we had it at the dealer when it was under warranty.
When we shut down an engine, we "Kill" the ignition system, so changing the spark advance will not solve a "run-on" issue.
Some may argue that excessive ignition advance can/will lead to higher cylinder temperatures ..... and I agree.
However, in most cases Run-On is caused by:
..... a lean low speed circuit fuel/air mixture
..... carbon deposits on piston decks
..... carbon deposits on combustion chamber surfaces
..... high cylinder temps at time of shut-down
..... excessive throttle opening during shut-down


By the middle of summer it would start sputtering again. Odd. Will be interesting to see what the numbers actually are with a timing light.
My suggestion:
DO NOT set BASE or Initial advance, and then walk away thinking that you are DONE!
Look further as to what the Progressive and Total Advance are doing, and at what RPM!!!!!
Click to expand...
 
OK..... let's assume that the ignition advance was excessive. In other words...... far too advanced from where the Factory wants it to be for any given RPM!
..... first, you may want to know that your 4.3L GM pistons are very prone to Detonation.
..... poor octane rated fuel and high cylinder temperatures perpetuate Detonation.
..... excessive ignition advance may perpetuate Detonation.
..... Detonation perpetuates high cylinder temperatures.
..... Detonation that has not YET caused any piston damage, will indeed prevent an engine from performing well..... such as bogging down!

No need for this information again..........not relevant especially after all the prior posts.
This piston design thing has run its course and has little if any place in this post.

The post does not refer to advance it is pointing to initial so again.......off target. The "mechanic adjusted initial only as a remedy to his run on issue. Did not even know which way he adjusted it.......big problem!! But your response has nothing to do with the issue in discussion.

Spark plug gap is normally predicated by the output voltage. With a High Energy output system, the gap can be increased some.
Keep the gap where it should be for YOUR ignition system!

If you looked that information is contained in earlier posts so again a no value added comment.........do you really just enjoy reading your own posts?

When we shut down an engine, we "Kill" the ignition system, so changing the spark advance will not solve a "run-on" issue.
Some may argue that excessive ignition advance can/will lead to higher cylinder temperatures ..... and I agree.
However, in most cases Run-On is caused by:
..... a lean low speed circuit fuel/air mixture
..... carbon deposits on piston decks
..... carbon deposits on combustion chamber surfaces
..... high cylinder temps at time of shut-down
..... excessive throttle opening during shut-down

My suggestion:
DO NOT set BASE or Initial advance, and then walk away thinking that you are DONE!
Look further as to what the Progressive and Total Advance are doing, and at what RPM!!!!!

Again.......Why all this?

Once base is set on these ignitions it is done. No ability to alter or change. Either it works or it doesn't. All that can be done is to confirm advance. that's it!

Spark advance is not the question or suspected issue here.......OMG read the information in the posts.......

Excessive initial timing can and will cause run on.............besides he clearly states 900 rpm at idle..............250 rpm over spec which is bad in many ways as I mentioned.....either main idle rpm adjustment bad or initial timing bad and main idle rpm adjustment bad combined, which is most likely true in his case.
 
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............................
kghost said:
OK..... let's assume that the ignition advance was excessive. In other words...... far too advanced from where the Factory wants it to be for any given RPM!
..... first, you may want to know that your 4.3L GM pistons are very prone to Detonation.
..... poor octane rated fuel and high cylinder temperatures perpetuate Detonation.
..... excessive ignition advance may perpetuate Detonation.
..... Detonation perpetuates high cylinder temperatures.
..... Detonation that has not YET caused any piston damage, will indeed prevent an engine from performing well..... such as bogging down!

No need for this information again..........not relevant especially after all the prior posts.
This piston design thing has run its course and has little if any place in this post.
YOUR EGO filled opinion is just one small opinion here!
Let the OP make his own decision.

The post does not refer to advance it is pointing to initial so again.......off target. The "mechanic adjusted initial only as a remedy to his run on issue. Did not even know which way he adjusted it....... big problem!! But your response has nothing to do with the issue in discussion.
Again...... in YOUR opinion!

Spark plug gap is normally predicated by the output voltage. With a High Energy output system, the gap can be increased some.
Keep the gap where it should be for YOUR ignition system!

If you looked that information is contained in earlier posts so again a no value added comment.........do you really just enjoy reading your own posts?
Again...... in YOUR opinion!

When we shut down an engine, we "Kill" the ignition system, so changing the spark advance will not solve a "run-on" issue.
Some may argue that excessive ignition advance can/will lead to higher cylinder temperatures ..... and I agree.
However, in most cases Run-On is caused by:
..... a lean low speed circuit fuel/air mixture
..... carbon deposits on piston decks
..... carbon deposits on combustion chamber surfaces
..... high cylinder temps at time of shut-down
..... excessive throttle opening during shut-down

My suggestion:
DO NOT set BASE or Initial advance, and then walk away thinking that you are DONE!
Look further as to what the Progressive and Total Advance are doing, and at what RPM!!!!!

Again.......Why all this?
Let the OP make his own decision as to whether or not the info was of any value to him.

Once base is set on these ignitions it is done. No ability to alter or change. Either it works or it doesn't. All that can be done is to confirm advance. that's it!
Precisely! And if it is incorrect, a change becomes necessary!

Spark advance is not the question or suspected issue here.......OMG read the information in the posts.......

Excessive initial timing can and will cause run on..
ONLY with regard to excessive advance causing higher cylinder temperatures.
Otherwise...... (and you should very well know this) ..... Ignition is CUT just prior to any "run-on" or "dieseling" occurance.
When Ignition is CUT, ALL Spark Ignition ceases to exist!

Once again Jack, you're allowing your ego to make you look silly!
Click to expand...
 
It has nothing to do with my ego. In fact I do not have one............

What I have is attitude from you being a PAIN IN MY A$$ from your misguided and chronically repeated posts. with way more or useless information than any boat owner (non mechanic) needs.

The reality is clear

You have little if any experience with Mercruiser. Without a doubt!

I would suggest staying on the Volvo forum and let them drink your KOOL-AID
 
There is an unused male ended black wire not being used just right of the distributor. Is this there for the ground of the distributor to keep it in the base timing mode for checking the timing? I wondered if Mercruiser put this there for that reason, or if it is for some other engine add-on. If not, A pigtail to a good engine ground is needed to check the timing to hold it in the base mode, correct? Sorry if my nomenclature is not spot on. going to check the timing and carburetor adjustment tonight. also going to put in a new thermostat just in case, it has been 10 years since the last one, even though I am sure the engine did not overheat to cause this problem.
 
No one said it over heated but you would not know this because your temp reading is too low.
It must be a minimum of 150 when engine is fully warmed up and typically its 160 ish......at normal idle. After running hard especially in warm water your temp gauge should be reading 160-170.....easily.

So along with your other issues, high idle speed, not knowing your base timing and any other issues you need to get your temp control/ reading correct.
Dont let that go the way it is because if you do over heat you wont know it until its too late.
 
Boat is fixed. The timing was WAY off, and the little "camel toe" marker is a pain in the ass to see. Ended up taking the back seat out to get a good check of it. Thermostat was stuck open, new thermostat put in. Noise was still evident after adjusting timing, etc. Determined it was the Gimbal bearing. Had that fixed. Now all is good, still want to get a new rotor and cap since it has been a few years since that was changed. Ran fine and got to 4,400 rpm as usual on Sunday.
 
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