Runs great until docking time

[Halstead666]

Hi, i have a 1996 5.7 merc that was running rough at start seems to need choke plate adj to a slightly more open position at start which I plan to do today. The other problem i have been having is that once started, it runs good heading out as I cruise to go fishing at 3000 rpms for approx 20 min then when I get to my spot and trim down and pull the throttle back slowly to approx 1000 rpm it starts to run rough again and usually stalls when it goes below 800 rpm, then it takes a while to start up again. I am wondering if it the choke setting from my previous problem although since the engine is now hot And choke plate fully open i am thinking not. To compensate for this I have set the idle way up to 900 rpms otherwise it keeps stalling. Any suggestions?

 

[wellcraft-classic210]

At lower rpms the fuel is delivered through idle ckts in your carb -- Higher rpms use the venturis. If its a 2 barrel Mercarb their is a screw on the front of the carb that adjusts that fuel mixture. Sounds like a carb passage cleaning / rebuild may be in order if its not the choke or screw adjustment as debris in the carb can cause these issues. A good fuel filter is critical to prevent recurrence also.