mercruiser carb, rochester, 3.0 4cylinder, adjustment questions

potatoe

Petty Officer 3rd Class
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May 27, 2010
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i have recently purchased a remanufactured carb for my mercruiser 3.0. my old carb had only one adjustment screw, besides the idle. the new carb has 2 adjusting screws, side by side. can anyone explain these to me? how to adjust them? im leaving it to the pros, but i do want to know. what happens when opening and closing these? thanks
 

Don S

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Aug 31, 2004
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62,321
Re: mercruiser carb, rochester, 3.0 4cylinder, adjustment questions

You bought the wrong carb. You had a Mercarb, you bought a Rochester. Merc stopped using the Rochester a long time ago. Early 80's I think.
 

potatoe

Petty Officer 3rd Class
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May 27, 2010
Messages
77
Re: mercruiser carb, rochester, 3.0 4cylinder, adjustment questions

is this a crappy carb? will it not work? thanks
 

Don S

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Re: mercruiser carb, rochester, 3.0 4cylinder, adjustment questions

You've got it, try it and find out.
 

dubs283

Vice Admiral
Joined
Jul 27, 2005
Messages
5,058
Re: mercruiser carb, rochester, 3.0 4cylinder, adjustment questions

the new carb has 2 adjusting screws, side by side. can anyone explain these to me? how to adjust them?

idle mixture screws

used for setting the amount of air/fuel bypassing the throttle plates at idle ONLY

turn clockwise to move in, counterclockwise to move out - note when the engine starts to stumble when turning either way, set at midpoint between engine stumbles
 
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