50 hp 2013 Mercury 4 stroke surging

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Sep 23, 2014
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Toronto Canada
Hope I have the correct forum and someone is familiar with this outboard.
Problem I have is the engine surges after running at wide open throttle for 30 seconds. The tach indicates 6,500 rpm which is over revving if the tach is correct. It does not sound as if ignition is completely shut off but power is rapidly reduced and them resumes in under a second. Is this the way a rev limiter would behave?
Does the rev limiter cut ignition or fuel injectors? Why does it take 30 seconds at 6,500 rpm before this happens?
I am asking because I started chasing a fuel starvation problem but perhaps the problem is the pitch of the propeller?
 
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Aug 20, 2003
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so the redline should be between 5500-6k?
I think I would check the rpms is it possible to see if it cuts out if you keep it under 5500?

You might be onto something.
 
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It appears Mercury recommended the max RPM operating range of 5,500 - 6,000 range. Change props to maintain that range and you should be fine.
 

WobblyElvis

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I don't have access to the boat very often. It's my son's in laws and he's the one dealing with it. The only gauge that works is the tach so I don't trust it. Perhaps he can download some app on his phone to measure rpm by sound. I was out on the boat this weekend and I didn't know the max rpm it should be turning but I do see that Mercury says 5,000 to 6,000 rpm. It appeared to be trimmed correctly. The motor is on a large pontoon boat. The prop may need to be bigger. I'm wondering if a rev limiter sounds like surging or fuel starvation and how is it limited, fuel or ignition?
 
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Jul 16, 2005
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Montague, NJ and Old Forge NY
Look up what the stock OEM factory prop is and what you have on it. Especially if the boat was bought used. Looks like it is hitting the rev limiter. Prop limits max RPM, limiter is there for when props out of the water.
Just like PWC's that when the pumps out of the water the limiter kicks in until pump is back into the water.
Used boats are famous for wrong props. Either whatever the marina had to get it going again after damage or someone trying to get more performance out of small motor.
My stock 60hp merc on a 18' pontoon will only turn 5200 wide open.
 
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