2006 Mercury 50HP BigFoot Low RPM

[Pshabou]

Hello everyone, I am new to the website.

I own a 2006 Bentley Pontoon, 24 footer. It has a Mercury 50hp Bigfoot also a 2006. I am the original owner and although not a lot of power, has done my family and I well.

My issue: The pontoon is slow, it always feels like the engine is working very hard. I was looking into purchasing a new prop, and when i was looking around, all the mercury prop selectors ask for rpm. My max RPM at open throttle is only 4,000. Mercury says it should be anywhere between 5500-6000 RPM.

I contacted my local mercury dealer and they want 125 dollars an hour to figure out the issue. He said it could be ignition, fuel or prop issues? I am real good at researching and fixing things myself, i just don't know where to start when it comes to this problem. If someone can maybe give me a couple ideas on where to start, that would be great.

Thank You
Paul

 

[MISC]

What pitch prop are you running now? It should be the last numbers stamped on the prop ending with "P". Naturally going down in pitch will speed the engine up. Each inch in pitch will speed the engine up about 200-300 rpms. That does not necessarily mean more speed. I had the same problem on my 20' pontoon with a 50 hp Mercury (not a Bigfoot) when I bought it last month but mine had too little pitch and it would rev almost to 6500 rpms. I went from an 8 pitch prop to a 10.5 and the max rpms changed to around 5800 so I don't quite run it wide open. The Bigfoot can handle a little more pitch but it sounds like you may have too much. I would think around 12 to 14 pitch would be right for your boat.

 

[Pshabou]

Hi MISC,

Thanks for the reply, I have a 13 pitch prop on the boat, 8.5 diam. I told the mercury people that, they told me i should still be running higher.

Any ideas on where I can start to troubleshoot?

Paul

 

[MISC]

That seems like the correct pitch but that diameter seems small for a pontoon. I am running a 10.5 pitch 12" diameter 3 blade on mine. I really feel like I could run a 12 pitch on mine and it would be perfect at 5500 rpms. I don't know really what direction to tell you to go as going to a larger diameter would slow the engine down more i think. Are you sure this is a prop issue and not a fuel delivery issue? Has it always had this problem? When I first got mine the carbs were jacked up from ethanol and all I could get out of it was 3,000 rpms. Pulled and cleaned the carbs and got it up to 4,000 rpms. Took them off again and soaked them in carb cleaner for a day and blew it out with compressed air and it would rev past 6,000 then. Make sure your carbs are not jacked up from running ethanol fuel first then look at other issues like the prop.