Mid Throttle Lean Condition

Rick Stephens

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These are 4 sets, each looks to be 4 pictures together of each plug.

Just for clarity, these are all after the motor ran rough for as long as it would run and then died while in a mid-throttle setting?

And you don't hve comparison photos of the plugs with the motor running decently at higher setting and then turned off?


These plugs look like at times the motor is running a teensy bit rich, evidenced by the soot on the housing. And at the time the motor quit it appears it might have been lean, the center electrode and insulator is completely free of soot and deposits and the ground electrode is shedding any deposits. It is positively not running rich at the time it died.
 

Goldie627

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These are 4 sets, each looks to be 4 pictures together of each plug.

Just for clarity, these are all after the motor ran rough for as long as it would run and then died while in a mid-throttle setting?

And you don't hve comparison photos of the plugs with the motor running decently at higher setting and then turned off?


These plugs look like at times the motor is running a teensy bit rich, evidenced by the soot on the housing. And at the time the motor quit it appears it might have been lean, the center electrode and insulator is completely free of soot and deposits and the ground electrode is shedding any deposits. It is positively not running rich at the time it died.
Hey Rick,

These pics are 1 set of 4 plugs, I just took extra pics from different angles so everyone could get a good idea of how they look.

Unfortunetly, i didnt take any pics of the plugs right after coming off plane for comparisson.

These pics are the plugs from the stutter/bog mode (900rpm to about 1100 rpm on the dash tach), i let it sputter for about 5 minutes then nudged the throttle forward and the engine cut off like it normaly does in that bad throttle range, i didnt restart the motor, i immediately pulled the plugs.

Not sure but the soot on the housing (if you mean where the threads on the plugs are) may be from the oil leak on the oil pan gasket or from where the oil that was leaking from the flame arrestor, or from the valve cover gasket that i replaced and may not have initialy tightened enough. I will take another look where the spark plugs are inserted to see if the area around the holes is oil free.

I have to look close to see if the soot/oil on the plug housing is from the inside or outside of the spark plug hole
 

Goldie627

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00:58:00 Disable Shift Interrupt
02:40:00 Engine Stalling
07:00:00 On Plane
09:32:00 Spark Plugs

 

Bondo

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Ayuh,.... Those plugs were seein' no gas, a lean condition,....
 

Rick Stephens

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Goldie,

First place is float level. Doesn't matter if it is brand new OEM carburetor - which is what we are talking here.

Next, since you're already in there, run al the ports with spray cleaner to make sure they are clear.

Double check you don't have an intake leak. I'm not totally sure if it is possible or likely, but since the intake and exhaust share the same manifold, a leak could be an internal crack if it isn't an external gasket. If you had an intake leak it would most effect throttle soon after opening. Idle can be adjusted a bit richer but low throttle settings are not easily adjustable and can be overwhelmed by a relatively small leak, causing lean condition.
 

Goldie627

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Goldie,

First place is float level. Doesn't matter if it is brand new OEM carburetor - which is what we are talking here.

Next, since you're already in there, run al the ports with spray cleaner to make sure they are clear.

Double check you don't have an intake leak. I'm not totally sure if it is possible or likely, but since the intake and exhaust share the same manifold, a leak could be an internal crack if it isn't an external gasket. If you had an intake leak it would most effect throttle soon after opening. Idle can be adjusted a bit richer but low throttle settings are not easily adjustable and can be overwhelmed by a relatively small leak, causing lean condition.

Thanks Rick!

Any idea how many milimetters at a time should adjust the float up? I know I want more gas in the bowl...

Carb was clean as a whistle but ill spray and blow through every hole that I can reach while the top is off

The last 2 times I checked for exhaust leaks I used starter fluid, evaporates super fast, I like it, I'll go leak hunting again just to call it extra thourogh
 

Rick Stephens

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Any idea how many milimetters at a time should adjust the float up? I know I want more gas in the bowl...


First thing is check to see if it is correct. I've never made one higher than specifications called for. I would expect problems doing that.

I don't know how to check for an internally cracked manifold without removing it. With it removed you can fill the intake side with acetone and see if any leaks into the exhaust side. Need a set of gaskets before trying that.
 

Goldie627

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First thing is check to see if it is correct. I've never made one higher than specifications called for. I would expect problems doing that.

I don't know how to check for an internally cracked manifold without removing it. With it removed you can fill the intake side with acetone and see if any leaks into the exhaust side. Need a set of gaskets before trying that.
i was going to wait on the oil pan gasket, but if i pull the motor i can just do it all at the same time...

im also thinking about that chattering noise coming from the pulley area, i went and got a stethascope but havent tried using it yet
 

Goldie627

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in the next few days ill check the float level but wont adjust it out of spec, there are 2 specs one for spring needle and one for solid so i might have to take the needle out too, no biggie, its cold out so ill snatch the carb off and bring it inside
 

Scott Danforth

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its either way lean or you have water entering the combustion chambers

water in the block would also give you clattering.
 

Goldie627

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its either way lean or you have water entering the combustion chambers

water in the block would also give you clattering.

Hi Scott, could you please watch the beginning of the video in post #25, give a good example of the chattering.

Last time I changed the oil it had no water in it, currently no water on dipstick....
 

Rick Stephens

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Goldie,

I have to believe you gotta have an intake leak. I watched the video again, the plugs are running lean enough that any deposits are being blasted right off the electrodes when you run down to that 1000 RPM range. I'd still love to see one of the plugs after running up on plane at 2k RPM. See if it shows lean up there too.

The way the carb works: when you throttle up and start accelerating, the carb is just starting to transistion out of low range ports onto the main jets right when it begins sputtering. When you jump on the throttle to blast past that, first the accelerator pumps dumps raw fuel and then the power valve is dumping fuel along with main jets. If this was a carburetor that was not application specific and we were calibrating it, we'd up main jet size right now and see where that got us.

BUT - this is an application specific carburetor. It is jetted and calibrated like every other Mercarb made for the 3.0L. Which leads me full circle back to an intake leak somewhere. @AllDodge, can you check me on my thinking please.
 

Goldie627

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Goldie,

I have to believe you gotta have an intake leak. I watched the video again, the plugs are running lean enough that any deposits are being blasted right off the electrodes when you run down to that 1000 RPM range. I'd still love to see one of the plugs after running up on plane at 2k RPM. See if it shows lean up there too.

The way the carb works: when you throttle up and start accelerating, the carb is just starting to transistion out of low range ports onto the main jets right when it begins sputtering. When you jump on the throttle to blast past that, first the accelerator pumps dumps raw fuel and then the power valve is dumping fuel along with main jets. If this was a carburetor that was not application specific and we were calibrating it, we'd up main jet size right now and see where that got us.

BUT - this is an application specific carburetor. It is jetted and calibrated like every other Mercarb made for the 3.0L. Which leads me full circle back to an intake leak somewhere. @AllDodge, can you check me on my thinking please.

Hey Rick, I want to show You the plugs on plane but not sure how to stop the motor while on plane. Is it as simple as turning off the key while on plane?
 

Rick Stephens

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Hey Rick, I want to show You the plugs on plane but not sure how to stop the motor while on plane. Is it as simple as turning off the key while on plane?

Yes. Run for a ways, 5 minutes, then turn the switch off. The prop and the water will kill the motor faster than you will believe. Poof, off. Pull a plug.

Rick
 

Goldie627

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Yes. Run for a ways, 5 minutes, then turn the switch off. The prop and the water will kill the motor faster than you will believe. Poof, off. Pull a plug.

Rick
Thanks rick, friday morning ill check the carb float to make sure its to spec, then saturday ill take the boat out to test, will report back
 

fishrdan

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Is it as simple as turning off the key while on plane?

...... If the exhaust shutters are burned out, that could hydro-lock the engine, when the stern wake catches up with the boat. It happened to me once when my ignition switch decided to give up the ghost running at cruise speed, the shutters were burned out and the engine cutting off, resulted in a hydro-locked engine....

I'd run it on plane for 5 min, come off plane quickly and blip the throttle just as the stern wake catches up, then cut the engine. ......
 
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