Idling too high

GMC2003

Petty Officer 2nd Class
Joined
Mar 3, 2011
Messages
119
1976 Invader
OMC 190hp stringer outdrive. Electric shift

Anyhow, my boat is idling too high, it does not have the original intake/carb setup. My uncle replaced it with a Holley 4 barrel carb and an Edelbrock performer 289 intake before he gave it to us. It has ran perfectly fine (Idling around 600 rpm) until yesterday. My question is where do I find the model number on the carb and where can I find a manual for the carb? I've tried adjusting the idle screw, but if I lower it any, the engine just dies. WOT is fine, and it doesn't sputter. Any help would be appreciated.
 
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