1980's 50hp - time for carb rebuild?

[Kawaga]

Hello all,

First timer here. We have a trusty cottage boat that I've been trying to do some trouble shooting with. Symptoms are: it starts and runs great with two people on board, but anything more and we can't get it to plane and it sucks power. We've never messed with the trim since it was new - always planed like a dream, so I've rulled out any setup issues. Like I said, it runs strong and reaches top speed with no issues with two adults on board. Three or more and the rpms still climb, but the boat just doesn't seem to want to come out of the water. Wondering if the carbs need a rebuild?

s/n is 7154223. Think it might be a 1986? Original prop.

Any help would be great. Thanks!

 

[carholme]

Re: 1980's 50hp - time for carb rebuild?

Kawaga;

That s/n comes up as a Canadian engine:

50 1981 EL 5531630 - 5949385 7143688

From here:

http://www.maxrules.com/models/Merc_model_files/40-50.html

Parts listing:

http://www.crowleymarine.com/mercury-outboard/275.cfm

Service Manual P/N 90-86135--5

http://cgi.ebay.com/ebaymotors/DEALER-MANUAL-MERCURY-MARINER-SERVICE-MANUAL-/140452275932

If you are getting max rpm with a light and heavy load but it won't come out of the water when heavy, it should be producing power and the fuel system should be OK. It sounds more like you have spun the prop hub. Do you have another prop the same size that you can check it with? If not, put a witness mark across the prop hub (between the metal and rubber parts) and try again with a heavy load and after the run, see if the witness marks are misaligned, indicating that the prop has spun on the hub.

Gerry

 

[ONERCBOATER]

Re: 1980's 50hp - time for carb rebuild?

what boat is this on? it may also be that you are just pushing the limit with more than two people and that planing is out of the question.... though I too would be checking for spun prop.

 

[Kawaga]

Re: 1980's 50hp - time for carb rebuild?

Gerry,

Thanks for your reply! Yes, this would be a Canadian (Ontario) engine - thank you for the links! I had a hard time doing the s/n match myself.

I guess there maybe more than one symptom happening here. Prop hub is a distinct possibility and would explain why it seems to be running strong even though we're going nowhere. At the same time, I wouldn't say we are running max rpm with a heavy load. So, maybe there is some fuel delivery issues when fully loaded at full throttle, but these are likely secondary to the prop issues. The prop hub is probably spinning, but there's enough friction that we are at least putting the engine under load.

I'll start by assuming the prop hub and go from there. Sounds like we'll have to get a new prop before I can troubleshoot any further. Considering it's still the original prop, a new prop probably wouldn't be a bad investment. Is our local marina the best place to order a new prop, or are there some good online dealers in Ontario I should consider?

Thanks again!

 

[ajgraz]

Re: 1980's 50hp - time for carb rebuild?

Not clear whether this is a new problem. Did it used to run OK with 3+ people onboard and only recently won't?

 

[Kawaga]

Re: 1980's 50hp - time for carb rebuild?

what boat is this on? it may also be that you are just pushing the limit with more than two people and that planing is out of the question.... though I too would be checking for spun prop.

Thanks for the reply! The engine is on a pretty simply fiberglass 15' boat - four seater. We remember family trips around the lake with four adults and a couple of kids and never had issues getting the boat out of the water. Used to ski behind the same boat with two adults on board - no chance we would get the boat to plane like that today.

Ok, spun hub seems to be the trend.

 

[Kawaga]

Re: 1980's 50hp - time for carb rebuild?

Not clear whether this is a new problem. Did it used to run OK with 3+ people onboard and only recently won't?

Yes, new problem. Never had issues with four plus on board. Cheers!

 

[carholme]

Re: 1980's 50hp - time for carb rebuild?

Kawaga;

Do the witness mark checking before you buy a new prop. If it is spinning, the marks will show you for sure.


Gerry

 

[Kawaga]

Re: 1980's 50hp - time for carb rebuild?

Kawaga;

Do the witness mark checking before you buy a new prop. If it is spinning, the marks will show you for sure.


Gerry

Yes, good point!

 

[Kawaga]

Re: 1980's 50hp - time for carb rebuild?

Ok, I had a chance to do some more test runs and troubleshooting over the long weekend. First up, here are some photos of the boat:

http://flic.kr/p/9MaXEd
http://flic.kr/p/9M8b7r
http://flic.kr/p/9M8b6a
http://flic.kr/p/9Mb2yY

Next, I take back my claim of the rpms climbing and the boat not planing. That's what I remember from last fall, but now that I've been testing it some more, it seems that the rpms don't max out and the boat just slogs along. Regardless, I watched the prop and the hub between a couple of runs just to make sure this isn't the issue. I didn't have a chance to mark the hub, but instead just remebered the orientation of the different parts and watched to see if they would shift.

Here's a photo of before:
http://flic.kr/p/9M8bbp

Here's a photo of after:
http://flic.kr/p/9MaXFo

The short answer is - I think there are no issues with the prop hub slipping.

 

[Kawaga]

Re: 1980's 50hp - time for carb rebuild?

Sorry, there's more (I needed to see if I can get the links working from the previous post).

So, back to my original problem ... I guess it can best be described as a poor performance issue. The boat will plane (reluctantly) with just me on board, but even with my 40lb son added to the mix it becomes questionable.

Here's a video of some test runs:

I decided to pull the plugs again and check for signs that we're running on all cylinders. Looked good to me.

Here are the plugs:

http://flic.kr/p/9M8NW4

I decided to replace the plugs just in case.

Here are the new plugs:

http://flic.kr/p/9MbD8J
http://flic.kr/p/9M8Rz6

So, back to my original thought ... time for a carb rebuild??

Here's a photo of the carbs:

http://flic.kr/p/9M8bcD

 

[Kawaga]

Re: 1980's 50hp - time for carb rebuild?

Oh ya, one more thing ... a family member took the boat to a local marina about a year ago for a "tune up". As far as I can tell from the invoice, they charged us $100 for going at it with a can of carb cleaner and taking it for a spin. They also did a compression test - the results were "ok". Both before and after the tune up, we have been suffering these performance issues. In other words, the "tune up" had no effect other than telling us that the compression is good (we think).

 

[jasonmmoore]

Re: 1980's 50hp - time for carb rebuild?

did you ever get this fixed? i have a 1985 mercury 50 horse with exactly the same problem.

 

[Kawaga]

Re: 1980's 50hp - time for carb rebuild?

Turns out the hull was full of water. We diligently drain the boat every spring and fall, but there was a section of the hull that was not draining through the plug. Ended up drilling a few holes to get the water out, patched them, and now we are installing a bilge pump.

Good luck!

 

[Maxz695]

Re: 1980's 50hp - time for carb rebuild?

That was my gues loaded with water somewhere. Looks like mine when the bait well has water in it. Do you have a Doel Fin on this thing? If so try removing it and see what happens