Idle mixture adjustment

BOWRIDERBENNY

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Mar 27, 2020
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1
I have a question about the idle mixture screw on a mercruiser 2 barrel. Mine seems to have a plastic spring loaded cap over it. Do I pull it off to get to the screw? Boat is a 2004 the original motor was a 5.0 vortec, I'm repowering with a 5.7 vortec.
 

Bondo

Moderator
Staff member
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Apr 17, 2002
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71,308
Mine seems to have a plastic spring loaded cap over it.

Ayuh,...... Welcome Aboard,........ It's non-adjustable, unless ya bust the cap off,......
 

Lou C

Supreme Mariner
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Nov 10, 2002
Messages
13,409
If repowering with a 5.7 you might want to check to see if the carb for them came with bigger jets. Then after it’s up and running monitor the color of the spark plugs center electrode insulator porcelain; it should be light tan or brown not blistered white which would show a lean condition.
 

Lou C

Supreme Mariner
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Nov 10, 2002
Messages
13,409
PS we had those caps on idle adjustment screws back in the '70s, and if I recall there was some kind of penalty or you might not pass inspection in some states if you removed them and did not replace them after doing the adjustment. I went through the same thing with a little Suzuki DF 2.5 4 stroke we have, it would never run quite right until the mixture was adjusted but in order to do that, a tin cap over the idle mix screw had to be removed. The dealer did this for us, but then covered it again in some epoxy...which somehow later disappeared....so it could finally be adjusted so it ran CORRECTLY.
 

Oldnbold

Seaman
Joined
Jun 27, 2017
Messages
60
In the dirt bike world and looking for optimum jetting and performance, when a bike was big bored but used the same carburetor and intake tract, the optimum jetting was using leaner jets vs fatter. This was tested with e/g analyzers on a dyno runs. Turns out, the bigger bore was sucking harder on the same jet making a too rich f/a ratio. Solution was leaner jets

just throwing it out there.
 

Cobe Marine

Cadet
Joined
Oct 5, 2019
Messages
16
I have a question about the idle mixture screw on a mercruiser 2 barrel. Mine seems to have a plastic spring loaded cap over it. Do I pull it off to get to the screw? Boat is a 2004 the original motor was a 5.0 vortec, I'm repowering with a 5.7 vortec.

To my knowledge (never claimed to have seen it all) the only 2brl carbs Merc ever used that would have the mixture screw capped would be the TKS. Not sure if you're trying to get at that screw due to an idle issue but if so, may want to check for proper function of the enrichment module beforehand.
 
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