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Cold Fouling of Spark Plugs Weber 4 Barrel Carb

S

settimo velo

Contributing Member
One of my engines has black deposits on the plugs. I suspect rich fuel mixture so I have been looking at the choke today. I followed the manual and checked the operation of the vacuum diaphragm and made some adjustments to the choke pull off, bending the linkage to set it at 15/64 in. I also checked the choke shaft and lever assembly to make sure it wasn't sticking from shut through to wide open. However, I can't see what mechanism is in place to fully open the choke plate when the engine warms up. How does this work and how can I check it?
 
More info needed: year, engine and SN to start. You don't see an electric or manifold actuated choke coil? On a cold engine the choke should be closed leaving about a 3/32" gap between the choke plate and the air horn. As the engine warms the the bimetal coil in the choke uncoils thereby opening the choke plate. The coils do wear out over time and need replaced.

If there is a manual fuel pump the diaphragm could be leaking which the carb vacuum sucks the fuel into the air horn via the yellow plastic tube on the carb. That would make the engine load up w/too much fuel and run very rich. Look for fuel in the yellow tube.
 
Thanks for your help. The engines are 4.3LX 1993-95 with the 4bbl carb. They do not have electric choke coils, so it's a bimetal coil that opens the choke plate. I will check to see if that is working when I have a hot engine. I guess that must be located in the base of the carb where the choke levers cross from one side to the other? When I bought this engine I found that this mechanism had been disconnected, so I refitted the spring clip to reconnect it. I also found that the engine had platinum tipped plugs fitted so I changed back to manufacturers spec. Maybe all of this was working around a problem that I now want to solve.

I have an electric fuel pump mounted on the engine and it seem fine but I will check for any suction into the carb.

If all that's OK then I was thinking of looking at the accelerator pump lever as that is set at hole 'a' (the rich setting), and also the idle mixture screws?
 
From Manual.

""""Dry, black deposits indicate rich fuel mixture or weak ignition. Clogged flame arrestor, flooding carburetor,
sticky choke or weak ignition components all are probable causes. If, however, only one or two plugs
in set are fouled, check for sticking valves or bad ignition leads. After correcting cause, service (clean, file and re-gap) plugs and reinstall."""""


It appears you have a bimetal spring connected to the choke by linkage. Is the bimetal spring a electric or the type that mounts to intake manifold and gets its heat source from the crossover (heat) of intake?

We need that info first.
 
for reference: is this your carb? http://www.mercruiserparts.com/Show...esc=CARBURETOR+AND+THROTTLE+LINKAGE(4+BARREL)

It shows the manifold mounted bi-metal coil. Those chokes used exhaust heat via a crossover pipe. If it has been disconnected it may be due to an upgrade to elec. choke. A picture of the carb set up would help determine what it has. You're sure there's no elec. wire to a hockey puck on the side of the carb? That would be an elec. choke.
 
The bi-metal spring wound coil unit is a Helix.
SEQ#27 calls this the "choke", when actually this is the Helix.

The schematic does indeed show that the Helix is mounted on the intake manifold, in which case you'll not have the Helix electric heating element.

As guyig says, the Helix (under normal cold conditions), pulls the linkage rod as to close the choke plate within the choke chimney.
As the Helix senses heat, it begins to open the choke plate.... and it should open it fully during normal engine operating temperature.



.
 
The crossover passage in the manifold is prone to plugging w/carbon and crud. The area should be too hot to touch if it is open.
 
kghost said:
From Manual.

""""Dry, black deposits indicate rich fuel mixture or weak ignition. Clogged flame arrestor, flooding carburetor,
sticky choke or weak ignition components all are probable causes. If, however, only one or two plugs
in set are fouled, check for sticking valves or bad ignition leads. After correcting cause, service (clean, file and re-gap) plugs and reinstall."""""


It appears you have a bimetal spring connected to the choke by linkage. Is the bimetal spring a electric or the type that mounts to intake manifold and gets its heat source from the crossover (heat) of intake?

We need that info first.
Click to expand...

I can't see any electrical connection to the carb. It does't look like guyjg's link with the choke (item 27) on the side. Based on the manual I have for my 4.3LX (1993-95) the carb appears to be Mercury Number 3304-9565A6 which is a Weber 9600. The exploded view on page 5C-18 doesn't show the bimetal spring and section 5C only covers the vacuum pull off aspects of the choke mechanism.

Is the bimetal spring is under the carb / on top of the intake manifold i.e. on the connecting rod that links the vacuum pull off coupling on one side of the carb with the linkage rod (item 35) on the other side of the carb. (None of this detail is shown in Mercruiser's exploded diagram in the manual e.g. http://www.marineengine.com/parts/m...31995/0f001220-thru-0f601126/carburetor-weber).
 
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the bi-metal coil has a retaining screw that holds it to the intake manifold...it should have a metal cover pressed over it. a link connects the free end of the coil to the choke opener.

If you don't see a can over the coil on the manifold, perhaps it has been removed - is there a flat area on the intake roughly 25mm x 50mm?
 
Not sure if this will help you any..... but take a look at these two style choke mechanisms.

These are example images only.

Here's the style with the Helix located at the intake manifold exhaust cross-over area.
The tin cover is necessary as to hold heat around the Helix.

313MDCDZ4SL.jpg


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Again... example images only.

Here's a Helix style using 12 v electric heating element.

Within the black plastic unit, will be both the Helix and the heating element.
This style uses a single power lead..... some will require both Pos and Neg.

$(KGrHqF,!q0E-ZStHzMYBPsB)wi0(!~~60_35.JPG



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securedownload-2.jpgsecuredownload-1.jpgsecuredownload.jpegsecuredownload-3.jpgHere are some pictures of my carb, taken this morning. Three of them show the carb cold, with the choke closed. I took pictures from the top and down both sides but I can't find anything like the helix cover shown above. I also took one picture of the carb with the engine running at 160F, so you can see the vacuum pull off operating and the choke opening. However, the choke plate is not fully vertical although it has moved passed the point that the vacuum pull off alone moves it to, so something else is working on it but I can't find it! Also, I'd be interested to know just how far the choke plate should be open at operating temperature, as it probably has another 30 - 40 degrees of movement in it to open fully vertical.
 
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settimo velo said:
View attachment 7902

Here are some pictures of my carb, taken this morning. Three of them show the carb cold, with the choke closed. I took pictures from the top and down both sides but I can't find anything like the helix cover shown above.

I also took one picture of the carb with the engine running at 160F, so you can see the vacuum pull off operating and the choke opening.

However, the choke plate is not fully vertical although it has moved passed the point that the vacuum pull off alone moves it to, so something else is working on it but I can't find it! Also, I'd be interested to know just how far the choke plate should be open at operating temperature, as it probably has another 30 - 40 degrees of movement in it to open fully vertical.
Click to expand...

If you have a Helix, it will located just above the manifold cross-over in the image above.

Let's take this one area at a time:

If during a cold engine, the choke plate is closing off the chimney, then it's rather safe to assume that the Helix is functioning... at least to some degree.
If during a warm engine, the choke plate is being opened, then again it's rather safe to assume that the Helix is functioning... at least to some degree.

During a warm engine, the Helix should be causing the choke plate to be fully open.

NOTE: on some carburetors, the function of the choke plate (related to it's open position), will either allow or prevent the secondary throttle plates from operating.

The vacuum pull off functions as per manifold pressure, so in essence the opening of the choke plate does not entirely rely on the vacuum pull off.


I'm betting that you do have the Helix there......., but it may be weak and not functioning correctly.

.
 
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Like Rick suggests, I believe you have the coil on the manifold...

see the red line I added to your pic - where does the lower end of the link it is pointing to attach to?

weberchoke.jpg
 
makomark said:
Like Rick suggests, I believe you have the coil on the manifold...

see the red line I added to your pic - where does the lower end of the link it is pointing to attach to?

View attachment 7906
Click to expand...



Yes this is what he has. The chimney style bimetal spring choke system. Used for years on auto's........still on marine.


The link arm pointed to is the the link arm going to the bymetal spring that should be eclosed in a metal shell as pictured above in Ricks post # 12 top image.


When cold, if you slightly activate the throttle the choke butterfly should snap shut.

when cranking it and vacuum is created the choke pull off should open the choke butterfly ~ 1/8 inch gap to allow air flow. That is the function of the choke pull off.

Once the motor is up to operating temp the bymetal spring should be completely UNWOUND in your case counter clockwise I believe so the link arm is as high as possible (almost touching the chimney housing) this is ALL the link arm/choke bimetal spring will give you.

There is a balance of how much the link arm can be adjusted (bent) to allow this to happen properly on both sides of the fuction (cold vs warm)

The choke butterfly may not open 100% and may stay closed by as much as ~25 % or so from what I have seen on these carbs.

First thing to to is to bend the link arm to get more opening on the choke butterfly when WARM. Small incriments only.

try to get about 50% more opening than you have now. Once you have accomplished this wait overnight and redo the cold activation, (activate throttle to allow ckoke butterfly to close. It should close shut or almost all the way to all the way shut ~1/16 inch max open would be ok if it does not snap shut still.

then start and let warm up and see where the choke butterfly ends up and let us know.

PS: RICK, most of us use the term bimetal spring. (last 30 plus years)
I for one have never heard of the word HELIX used to describe any choke components. I have heard it used for many other helical devices but not a carb choke system.
Not saying it isnt so, but injecting lesser know/used word to possibly more "acuratley" describe something only confuses.............just sayin.........
 
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Rick/Kghost...can that bimetal spring be tightened on the shaft to take up the slack from wear?

I remember back in 1972 I would remove the assy. from the manifold and clean the crud off the bottom of the base on my Dodge Charger...loved that car! In 1978 I had to clean out the plugged crossover passsage...used a coat hanger and some carb cleaner.

Just a thought...if the exhaust manifolds were replaced at some point installing the wrong gasket would stop any exhaust from getting into the crossover passage. That would make it slow to open.
 
They few I've had apart, the "inner" end of the spring is fixed in a slot so I don't think there's anything to tighten...

If the intake was removed and the wrong gaskets used, the crossover would be blocked...for how long would depend upon the gasket material...most composition gasket won't stand up to the heat so that issue wouldn't last long.

If the spring is sound, I'd look for interference between the can and the link or spring...another possibility is the link was lost somewhere in time and replaced with something else that may not be appropriate.
 
They few I've had apart, the "inner" end of the spring is fixed in a slot so I don't think there's anything to tighten...

If the intake was removed and the wrong gaskets used, the crossover would be blocked...for how long would depend upon the gasket material...most composition gasket won't stand up to the heat so that issue wouldn't last long.

If the spring is sound, I'd look for interference between the can and the link or spring...another possibility is the link was lost somewhere in time and replaced with something else that may not be appropriate.

And 2X on Kghost's thoughts on "helix"...a helix is akin to a stretched out slinky...
 
kghost said:
Yes this is what he has. The chimney style bimetal spring choke system. Used for years on auto's........still on marine.


The link arm pointed to is the the link arm going to the bymetal spring that should be eclosed in a metal shell as pictured above in Ricks post # 12 top image.


When cold, if you slightly activate the throttle the choke butterfly should snap shut.

when cranking it and vacuum is created the choke pull off should open the choke butterfly ~ 1/8 inch gap to allow air flow. That is the function of the choke pull off.

Once the motor is up to operating temp the bymetal spring should be completely UNWOUND in your case counter clockwise I believe so the link arm is as high as possible (almost touching the chimney housing) this is ALL the link arm/choke bimetal spring will give you.

There is a balance of how much the link arm can be adjusted (bent) to allow this to happen properly on both sides of the fuction (cold vs warm)

The choke butterfly may not open 100% and may stay closed by as much as ~25 % or so from what I have seen on these carbs.

First thing to to is to bend the link arm to get more opening on the choke butterfly when WARM. Small incriments only.

try to get about 50% more opening than you have now. Once you have accomplished this wait overnight and redo the cold activation, (activate throttle to allow ckoke butterfly to close. It should close shut or almost all the way to all the way shut ~1/16 inch max open would be ok if it does not snap shut still.

then start and let warm up and see where the choke butterfly ends up and let us know.

PS: RICK, most of us use the term bimetal spring. (last 30 plus years)
I for one have never heard of the word HELIX used to describe any choke components. I have heard it used for many other helical devices but not a carb choke system.
Not saying it isnt so, but injecting lesser know/used word to possibly more "acuratley" describe something only confuses.............just sayin.........
Click to expand...

The boat is going back in the water at the end of the month so I'll be able to get the engine really hot then and carry out the adjustments you suggest. I'll let you know how I get on. It's definitely worth getting the choke set right given the crazy price of fuel here in the UK! Thanks very much for your help.
 
kghost said:
PS: RICK, most of us use the term bimetal spring. (last 30 plus years)
I for one have never heard of the word HELIX used to describe any choke components. I have heard it used for many other helical devices but not a carb choke system.
Not saying it isnt so, but injecting lesser know/used word to possibly more "acuratley" describe something only confuses.............just sayin.........
Click to expand...

Well, perhaps this is a generational and/or regional thing.
I began doing mechanical work in the mid 60's and in Oregon state where I learned the term the "Helix".

I'll tell ya what...... I'll compromise with you guys, and I'll start calling it a bi-metal coil-spring-a-ma-jiggy Helix! :D

I'll gladly do this for you guys, if you'll start calling an engine an "Engine", instead of calling it a "Motor"! :D


.
 
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settimo velo said:
The boat is going back in the water at the end of the month so I'll be able to get the engine really hot then and carry out the adjustments you suggest. I'll let you know how I get on. It's definitely worth getting the choke set right given the crazy price of fuel here in the UK! Thanks very much for your help.
Click to expand...

There is no need to wait for sea trials........It should work while running on a hose.
 
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