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2003 merc 40hp 4strok wont run right after running then restarting

glsteingass

New member
We have a2003 40hp murcury 4stroke on our pontoon boat it has started giving us fitz we will run it for a while /15 min to 45 min/ then we will shut it down for /5min to 20 min/when restarting it will run terrible sounds like maybe on one cyl stalling and very little power then after 10 min or more of restarting it will up and run sometimes. Other times we need to dock it and go back 1 or 2 hrs later and it will run great again .I change fuel filters and plugs and drain replace gas every year motor pees like a 10 year old . Any help on this would be great
 
Try a cylinder drop test at idle, pull one spark plug wire one at a time,listen for sound and rpm change. a timing light could verify plugs are getting spark, If there is no rpm change on a cylinder, There's your culprit
 
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