2005 Mercury 4 stroke 50HP ???

[Nauteal]

Saturday Night

I have a friend who has offered me his 2005 Party Barge with the 50 HP 4 stroke. In-spite of him not treating the cosmetics of the boat too well, the boat looks pretty decent. The boat has been parked on a fresh water lake and today I went over and started it. It ran very smooth. It shifted smoothly, but when getting underway the RPM's never went above 2000 at full WOT. I see this motor is rated for 5500 to 6000 at WOT.

I did not take the engine cover off to check anything out as I wanted to get some feedback as to what the problem(s) might be. And possible things to look for. I have done the light maintenance on other boats I have owned - Mercruiser straight 6 and V6 motors. Mercury Force 75, 1960's Evinrude 75, etc.

Lastly as another independent opinion and not knowing what pitch prop is on this motor yet - Any idea what this motor should be able to push this 22 foot pontoon boat up to speed wise on flat water.

Thanks for your replys - It has been a while since I have posted.
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Next day (Sunday), I was crunching on this in my sleep last night and taking a step back and looking at things. I have got an idea what the problem is and I really would like to get some feedback. I have read other post on the site who have had similar problems, but they never got any feedback. Help me out now this is bugging me!

 

[Silvertip]

Re: 2005 Mercury 4 stroke 50HP ???

Speed should be in the 18 - 20 MPH range with a light load. There is something seriously wrong with this rig if it won't rev over 2000 RPM. Suggested problems are tachometer set incorrectly or simply defective is the first thing to look at. You've indicated ownership of other outboards so when the tach on this rig reads 2000 rpm does the engine actually sound like a fast idle or does it sound like wide open throttle. What is the boat speed at 2000 rpm All of this should be evident whether the problem is engine or tach. The boat itself can limit speed if the tubes are covered with algae or have water in them. The prop would have to be wrong (very wrong) to limit rpm to 2000. Is this a Big Foot (2.33:1 gears) or standard lower unit.

 

[JB]

Re: 2005 Mercury 4 stroke 50HP ???

Could be the control not opening throttle all the way.

Could be it dropped a cylinder.

Could be severely overpropped.

Need a lot more info, and the model number, before we can go any deeper than that.

 

[Nauteal]

Re: 2005 Mercury 4 stroke 50HP ???

Speed should be in the 18 - 20 MPH range with a light load. There is something seriously wrong with this rig if it won't rev over 2000 RPM. Suggested problems are tachometer set incorrectly or simply defective is the first thing to look at. You've indicated ownership of other outboards so when the tach on this rig reads 2000 rpm does the engine actually sound like a fast idle or does it sound like wide open throttle. What is the boat speed at 2000 rpm All of this should be evident whether the problem is engine or tach. The boat itself can limit speed if the tubes are covered with algae or have water in them. The prop would have to be wrong (very wrong) to limit rpm to 2000. Is this a Big Foot (2.33:1 gears) or standard lower unit.

Thanks for your initial reply. I am not near the boat today where I can harvest the information from the motor, but here are some of my thoughts. The motor had good pea coming out the back when running. I could achieve a high RPM in neutral - so I am thinking 2 directions to begin with problems could exist. (1) From what I understand the lower unit has been in the water for 2 years and doubtfully the gear oil has not been changed and yes there was a coating of algae on the outside of the leg. I have never had one of my lower units breach and have water mix with the gear oil, so I am not experienced with this. I do question if this has happened. This makes me wonder if the lower unit is being restricted holding the motor back, but it didn't sound like it was struggling. It just sounded very quiet since I have been used to 2 cycle outboards. The RPM's sound natural for 2000. (2) I didn't have a compression gauge with me to check the cylinders so I wonder if something has occurred here. Either Or both places.

And JB it occurred to me that the throttle may have some how slipped making the issue simple.

 

[Silvertip]

Re: 2005 Mercury 4 stroke 50HP ???

Be aware that reving an engine in neutral and having it rev to the moon means absolutely nothing. The engine can be running on half it's cylinders and still rev quickly in neutral. Put a load on it and lack of power becomes immediately apparent. Whether or not the lower unit oil has been changed is very likely not the issue. Lack of lub would have locked up the motor, not just slowed it down. If the motor is a Big Foot, it will say so on the engine cover. If it doesn't, then you have a standard lower unit. That is not the best motor for pontoon service (which is why Merc sells the Big Foot which has deeper gears and is able to run a larger diameter prop).

 

[comfun1]

Re: 2005 Mercury 4 stroke 50HP ???

I think what you are saying is the engine is reving up but the tach will not go above 2000 rpm. I have a 1996 60hp that has had this same problem in the past. I don't remember exactly what it was but my problem was electrical in nature. The engine ran and reved fine it was just that the tach did not accurately reflect the rpm's. I hope someone here can help you.

 

[Nauteal]

Re: 2005 Mercury 4 stroke 50HP ???

I think what you are saying is the engine is reving up but the tach will not go above 2000 rpm. I have a 1996 60hp that has had this same problem in the past. I don't remember exactly what it was but my problem was electrical in nature. The engine ran and reved fine it was just that the tach did not accurately reflect the rpm's. I hope someone here can help you.

Thanks Comfun1, I am not a professional, but I have been around boats long enough to know when something doesn't seem right. The RPM's do kick-up in neutral, so the tack is not the issue. Now this is my first experience with a outboard 4-cycle. The speed and power being generated by the motor seem consistent to 2000 RPM's. From what I have read this motor should be able to achieve 5500 to 6000 RPM's under a normal load and a properly pitched prop.

 

[Silvertip]

Re: 2005 Mercury 4 stroke 50HP ???

We can discuss this over and over again but unless we know if this is a Big Foot motor, what prop you have, whether the tach is accurate, and whether the engine is actually running on all cylinders all "assumptions" are just that. It's time to do some actual diagnosing. I will say again -- the prop would have to be so far wrong that I doubt there is one with enough pitch to actually make that engine lose 4000 rpm. 2000 - 2500 rpm is about the range where "limp home" mode is activated (as in an overheat condition).

 

[Nauteal]

Re: 2005 Mercury 4 stroke 50HP ???

You are right, and I have linedup a marine tech versed in Mercury 4 strokes to go out with me Monday to check it out. I will post back the results then. Thanks.

 

[cr2k]

Re: 2005 Mercury 4 stroke 50HP ???

First thing to check is the prop. If it has a regular boat prop on it it will be way over propped. A barge like that needs a very low pitch prop.

 

[Bryan9633]

Re: 2005 Mercury 4 stroke 50HP ???

I would suspect a stator going bad on the high speed side. Stators have low speed windings and high speed windings. At about 2500rpm the low speed windings cannot generate enough power to the plugs so the high speed windings pick up the slack. Sounds like they are not doing their job.

 

[Nauteal]

Re: 2005 Mercury 4 stroke 50HP ???

OK. Well I am back . . . later than I said. I feel like the wide mouth frog trying to swallow a whale. Like I said in my initial post I had not bothered to pull the cover off the motor or examine it that close in my initial visit with the boat. Once I did come back with a marine tech it was quickly discovered it was NOT a 4/stroke - (Wide mouth frog here). It turned-out to be a 50HP 2 stroke with oil injection. The compression came in fine at around 120 per cylinder. The problem turned out to be in the lower 2 carbs. The lowest one was completely blocked-up. That is fine now.

The next thing I am going to be dealing with is what I think is possibly the wrong prop being on this boat. The motor by numbers is a 2005 50elpto. If I throttle-up slowly it transitions fine through to top speed. If I lay it down like I would on a ski boat pulling a skier it get some vibration noise in the mid-range speed. I am not totally sure how to describe it, since I have never had an issue on any of my other boats when fine tuning the prop selection.

Lastly comparing this boat to my 24' Playcraft - w/75hp Force vs. this Party Barge 22 - w/50hp. The weight difference between the boats is around 6-to-700 pounds. The Party Barge weighs more and has round logs. The Playcraft has U-logs. The Playcraft sits lower on the water and tracks very well. While the Party Barge sitting high on the water is harder to dock in the wind. The only disadvantage I can find with the Playcraft is waves slap the bottom of the deck easier which causes a bucking like ride sometimes when cruising.