need help with quadrajet idle mixture

beaug

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Jul 31, 2017
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MerCruiser 5.0 thunderbolt 4. I have rebuilt the carburetor twice and replaced the fuel pump. When I adjust the mixture screws all the way in the rpm increase and the engine runs better i also notice with the screw all the way in it dribbles fuel out of the primaries ventures if a back out the mixture screws it stops dribbling fuel. any help would be appreciated thanks
 

alldodge

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notice with the screw all the way in it dribbles fuel out of the primaries ventures if a back out the mixture screws it stops dribbling fuel

This sounds like your float level is to high. This is how the float is adjusted

Carb float Adjust.jpg
 

beaug

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Jul 31, 2017
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I have a 4 barrel I set the height to specs that came with the rebuilt kit
 

alldodge

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Your carb is flooding the motor, this is way when the idle screws go all the way in the rpms increases. The pic above is just for illustration.
 

kenny nunez

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Jun 20, 2017
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First double check the timing. Usually when. Q jet bubbles out of the primaries the idle is set too high. What is happening is the throttle blades are uncovering the intermediate circuit. The idle moisture screws should be 1.5 turns from seat + or minus 1/4 turn. Another cause can be a plugged air bleed in the primary side. Those holes are very small and it does not take much to plug them as well as the brass tubes in the float bowl. Also be sure there are no vacuum leaks.
 

beaug

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Jul 31, 2017
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I check my timing at 8 btdc. Fuel pressure at 8 psi. Pulled of the carb and the bottom was wet with fuel. I put my buddies edelbrock marine carb and it ran great was able to adjust the idle mixture so do I go with a edelbrock or find reman quadrajet
 

Grub54891

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Jun 17, 2012
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Could be just a bad float. I've had that happen a few times, now I just replace them during an overhaul.
 

kenny nunez

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Jun 20, 2017
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Remove the throttle plate and reseal the 2 plugs in the bottom of the float bowl. There is usually a piece of foam covering the plugs. J B weld is a good product to seal these plugs. This has always a problem with those carberators.
 
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