Merc 50 Power Loss?

[CWARK]

Hi,
I have a 2004 Mercury 50 HP 2-stroke. I have it on a 16 ft aluminum boat. It has a 4 blade 11 pitch prop. Top speed was 38 mph @5500 rpm. Now it will only due 30 mph and it will go no higher than 5000 rpm. Does anyone have any idea what has happened? It starts great and idles and runs fine and smooth. I am no mechanic, but I don't want to go broke over something that may be simple. Thanks for any help.

 

[Yepblaze]

Re: Merc 50 Power Loss?

It could be so many things.

It's winter here.

Is it full of frozen water somewhere?

 

[DJ]

Re: Merc 50 Power Loss?

You are most likely losing a cylinder. You need three things for each cylinder to pull its weight.

1. Spark.

2. Compression.

3. Fuel.

You are missing one, or more, of those on one cylinder.

Spark is the easiest to check. Get a spark tester from the auto parts store (cheap).

Next, check compression. All cylinders should be within 5-10 psi of each other.

If those two are good, you have a clogged carburetor. That needs to be addressed as it will damage your engine.

 

[CWARK]

Re: Merc 50 Power Loss?

Thanks. What would cause the compression to go bad? Can it be repaired if that is it? The motor has probably less than 20 hours on it. The clogged carb is definitely possible as it has been sitting for awhile, although I followed Mercury's storage instructions. Can that be cleaned with some sort of treatment or do I need a mechanic to clean it? Again thanks & Merry Christmas.

 

[CWARK]

Re: Merc 50 Power Loss?

OK. The spark and compression are both good. What can I do to get the fuel system working properly? Thanks.

 

[Silvertip]

Re: Merc 50 Power Loss?

First, you are not going 38 MPH with an 11P prop at 5500 RPM. In fact you can barely hit 30. So you are now getting exactly what the prop calculator says you should get --- 30 MPH.

 

[CWARK]

Re: Merc 50 Power Loss?

Where is this prop calculator? I did get that before, but it was in 2004. I am now starting to wonder if something hasn't happened to my boat. I have two friends with similar setups going in the high 40s albeit with 14 pitch props. is there 15-mph difference in these props? Thanks for the input.

 

[CWARK]

Re: Merc 50 Power Loss?

My friend checked the timing just for giggles and it is not advancing at all. We checked his identical motor and it moves alot. What could cause this? How can this be adjusted? We can't figure it out.