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MerCruiser 3.0 Rough Idle after New Carb put on

marygee1's Avatar

Join Date: Dec 2000
Posts: 116

06-30-08, 11:30 AM   #1  
MerCruiser 3.0 Rough Idle after New Carb put on

Long story...moter woul "Diesel" badly when shut off...my mechanic said that he read this was a needle valve in carb problem, we dicussed rebuild -vs- put on a new carb...we put on anew cardb. Came back and would start but shook the whole boat it was idling so rough...it would smooth out after about 5 minurtes of run time. THEN...we heard a hiss-hiss-hiss sound...mechanic said blown head gasket...replaced.

Now still idling very rough but will smooth out after 5-10 minutes then no problem...still deisel's on shut down but just barely. Is the rough idle a choke problem ? What should I look at for rough idling. I knoow I need a new mechanic but please offer suggestions

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thezster's Avatar

Join Date: Aug 2005
Posts: 2,268

07-01-08, 06:11 AM   #2  
You're right - need a new mechanic!! Sounds as if your carb is running rich (dieseling and rough idle). As the engine warms up, the heat generated tends to, more or less, override a rich mixture problem. Could also be your choke is not opening up enough initially, assuming it's an electric choke - that opens the butterfly after a few minutes from starting. On the other hand, a new carb tends to run pretty well right out of the box, so to speak... making me wonder if you've got something else going on.

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