98 Merc 4.3l Lean on one side?

[extreme76]

98 Mercruiser 4.3l.
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New plugs, cap, and rotor this spring
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Since getting it out this spring it has a few issues. It will sometimes backfire through the carb usually only when cold and when you give it gas. It "pops" the worst on the muffs. It also has poor acceleration and will not reach wot. It did one day for a short period (surged) but hasn't since.
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I pumped gas out of the bottom of the tank and did not find any water.
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I believed it was a lean condition so I pulled the plugs. The plugs on the port side show lean, if any thing rich on the starboard. That is 1, 3, and 5 plugs were snow white, 2, 4, and 6 were dark brown to black.
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I am assuming this is a carb issue. Could it be anything else? 2 barrel Mercarb, if it is the carb could someone explain to me how they work and why it would be lean on only one side?
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Thanks again guys.

 

[Bondo]

Re: 98 Merc 4.3l Lean on one side?

I am assuming this is a carb issue. Could it be anything else? 2 barrel Mercarb, if it is the carb could someone explain to me how they work and why it would be lean on only one side?

Ayuh,... Go ahead,+ Rebuild the carb,...
You'll have a better understanding of How it does what it's doing after you rebuild it...

 

[ENSIGN]

Re: 98 Merc 4.3l Lean on one side?

With the engine running spray the lean side of the intake manifold where it meets the cylinder head with some carb cleaner and see if the idle speed changes.You have the synptoms of a vacuum leak.

 

[extreme76]

Re: 98 Merc 4.3l Lean on one side?

Update
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The popping and stumbling was not the carb. I finally checked the timing (I know, I should have done that when I changed the cap and plugs). It was about 2 degrees ATDC, set to 10 BTDC in base timing mode and now she purrs like a kitten. I am going to run it some and see if one side still shows lean as I realize the 2 issues may have not been related.