Mercruiser 420 Stumbles
08-23-2020, 08:05 AM
#31
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Ran 9 hours yesterday, first four hours the boat ran perfect. No issues, ran right up to WOT no problem. No issues after restarts. After docking at a tiki bar for an hour and a half, idled out of the cove, starboard engine stumbled and died out. Check carb bowl, full of fuel. Fired the engine back up and ran for another hour without issue. Upon restart, I revved the engine out but it stumbled during the entire RPM range then cleared itself out. Beached at a local sandbar for about an hour, fired up and got on plane ran four a few minutes then the port engine stumbled and died out. Restarted and ran back to the ramp without issue. I am at a loss here. Going to replace fuel pumps this week but I don’t think that will solve anything considering when the boat is running, it runs great. Spinning 21P to 4900 RPM at 61 MPH, full tank and four people. This is a hard issue to troubleshoot since it is intermittent and I cannot reproduce the problem.
08-23-2020, 08:35 AM
#32
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Ran 9 hours yesterday, first four hours the boat ran perfect. No issues, ran right up to WOT no problem. No issues after restarts. After docking at a tiki bar for an hour and a half, idled out of the cove, starboard engine stumbled and died out. Check carb bowl, full of fuel. Fired the engine back up and ran for another hour without issue. Upon restart, I revved the engine out but it stumbled during the entire RPM range then cleared itself out. Beached at a local sandbar for about an hour, fired up and got on plane ran four a few minutes then the port engine stumbled and died out. Restarted and ran back to the ramp without issue. I am at a loss here. Going to replace fuel pumps this week but I don’t think that will solve anything considering when the boat is running, it runs great. Spinning 21P to 4900 RPM at 61 MPH, full tank and four people. This is a hard issue to troubleshoot since it is intermittent and I cannot reproduce the problem.
08-23-2020, 09:03 AM
#33
Gold Member
Gold Member
Sounds electrical to me, I would check voltage to starter solenoid cold (when it works) then when it does it again, check and see if you are getting a good 12v. If so, probably bad solenoids or grounds (clean all ground anyways, can’t hurt)
on another Note, I am building some 420 clones and there is really nothing online to reference. Could you post a bunch of pics of the 420s from all angles since you have a nice original set? Not many left out there
on another Note, I am building some 420 clones and there is really nothing online to reference. Could you post a bunch of pics of the 420s from all angles since you have a nice original set? Not many left out there
08-23-2020, 09:31 AM
#34
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