Problem with my Mercury 50 from 1986

[Sprokkel]

Hello All,

First a short introduction of myself.
Iam Dennis Camps from the Netherland and iam 34 y old.
Iam in to boating now for about 6 months.

The boat that i have is a polyester speedboat V hull thats about 5 m in length.
It runs with a mercury 50 hp two stroke.

I have some problems with it and maybe you can help me understanding this problem or help to find a solution for it.

Problem 1
When i start the engine ( it does not matter if its warm or completely cold) i need to set the high idle lever on my remote to full.
Then it starts imidiately at pretty high throttle ofcourse. Then i close the lever completely and it runs at a steady ( little high to my taste ) idle.
If i dont set the lever to high idle it wont start.

Problem 2
This problem is maybe more interesting.
When i run the boat without the engine cowl its runs perfect ( except for starting issue )
i can run it infinite at wot and it wont hesitate. i get around 50km/h out of it.
Now when i put the cowl back on and run it at wot for about 10-20 seconds and then it bogs down completely and instantly. At that point i go to neutral and the engine keeps running.
I wait for aprx 3 seconds and i can go to WOT again for about 20 seconds and then the same thing happens.
When i go to WOT it does not hesitate and gives me full power imidiately.

To make it more interesting. Sometimes problem 2 is also occuring when on half throttle.

What did i do and what kind of engine is it:

Mercury 50 2 stroke 1986
I replaced all fuel lines including new gas tank en bulp. vent on gastank is always open when i run it.
changed spark plugs
cleaned carbs
replaced fuel pump.
engine has new impellor and its delivering a strong pee out of the pee hole wich feels cool.
changed fuel filter
needles are set to aprox 1.25 out from fully closed.

so without cowl all is fine except for the starting issue.. but maybe thats normal.
with the cowl on problem 2 is there.

Allready very glad that u help me

Regards,
Dennis

 

[rbmatthews]

Hi Dennis

First of all, welcome to the forum.

I am not sure if I can address all of your questions, but can at least give you some pointers for one or two of them.

Problem 1: The older Mercurys/Mariners had a fuel enricher valve rather than a choke - essentially this was a solenoid valve that let petrol from one of the carburettors into the crankcase to increase the fuel/air ratio for starting. This was operated by the key on the remote control console - there is a position on this key just before the engine cranks over which you should hold it on for 2-3 seconds to let it operate (you should hear the click of the solenoid) before starting. It is possible this solenoid is not operating, or the rubber hoses that lead to it or goes from it are perished, so check that first, and that petrol is flowing through it when operated.

Problem 2: Difficult to say what is happening here. Check that the air intakes in the cowling are not blocked up - you could clean or replace the foam filters to make sure. Another thing might be that the cowling is somehow interfering with the petrol line, perhaps kinking it so that the fuel is not getting through. When you cleaned the carbs, did you also clean out all the little tubes and passageways with compressed air, and make sure that the float levers have the correct gap from the needle valves and are operating freely? Check also that the linkage between the carbs is operating correctly and that each carb is balanced (do this by putting a plastic tube into the air intake of each and listening to it with one ear and adjust the idle screws until they all sound the same pitch). For the idle screws, they should be around 1.5 turns out from fully closed, although 1.25 sounds reasonable, but you could try adjusting these out or in a bit further to see if it makes any difference.

Can't think of anything more at the moment, but hope this helps
R.

 

[VicS]

Problem 2 might be due to a leak of exhaust gas under the cowl.

If you do not get these problems solved here i recommend the Mercury/Mariner board at iBoats: http://forums.iboats.com/forum.php

and/or the one at MarineEngine.com: http://www.marineengine.com/boat-forum/forum.php

 

[Sprokkel]

Hello,

Thank you for the usefull reply's i will go and sort them out. When i have an update i will post a reply here.
Since its winter here now its kinda hard testing but i can deffenately check everything out that is mentioned here.

Regards,
Dennis

 

[cygnusv]

Problem 2 might be due to a leak of exhaust gas under the cowl.

If you do not get these problems solved here i recommend the Mercury/Mariner board at iBoats: http://forums.iboats.com/forum.php

and/or the one at MarineEngine.com: http://www.marineengine.com/boat-forum/forum.php

If it's the same motor - 4 cylinder 1000cc 2 stroke petrol - I had exactly problem 2. Turned out it was the exhaust manifold leaking and choking the engine. Another problem I had was with the prop. I remember being in Whitby harbour with an old Whitby lifeboat (trip boat) trying to bully me out of the way. I put the hammer down - and slowed right down! Turned out that the original Mercury prop runs on a metalastic bush that had perished and couldn't take the torque. Replaced it with a carbon fibre propeller and not only did it not stall anymore - it could fly! And often did - from one wave to another!

Also a 5 metre boat

 

[Sprokkel]

Hi again,
So i have this question since i have my lower unit removed at the moment.
When you instal a new impellor and its not " broken in yet" will the engine be harder to start ?
I can imagine when the impellor is not broken in yet the driveshaft needs more torq to turn it around cause of the friction of the impellor.
is this true ? and therefore after a while it gets better?

cheers,
Dennis

 

[rbmatthews]

I suppose there might be a slight difference, but I have to say that I have never noticed it in all the impellers that I have changed. The impeller, after all, is just a rotor with rubber vanes, and after the first revolution or so, the vanes will be aligned the right way, assuming it was all installed correctly. And the amount of power it would take to drive the impeller would be pretty small in relation to the power output of the engine, I would have thought.

R.

 

[jfm]

Not much to add really...

1. Check the "Choke" system is working. It's likely an enrichener on this model not a choke as already mentioned. The solenoid is switched by pushing the key in, and you must do this before turning the key to engage the starter motor, not during. The solenoid clicks, and you see arms move on the sides of the carbs. The manual used to say do NOT open the throttle too wide while using the enrichener

2. The cowl thing feels like air starvation or exhaust leak as already mentioned. Either must be fairly obvious to diagnose. If you remove JUST the front plate of the 3-part cowl assembly, that will allow fresh air in but not (much) ventilate exhaust out so that would tell you. also if there is an issue with cowl kinking a fuel line removing just the front cowl part will also indicate that

3. The extra break in torque of a new water pump impeller is ~zero. The pump is tiny.

The carbs are very sensitive on these engines so doing them up and backing off is unlikely to get you anywhere near optimum I'm afraid. Especially as there are two carbs, and they want to be tuned together pretty well

Remember with a running outboard, there are only 3 things that can be at fault: fuel, spark and air, and normally it is one of the first 2.

 

[Sprokkel]

Hello,
Long time no see..
I have found what the problem was.
When i set the engine in to gear a big arm on the engine is moving. This arm was pinching the main fuel line till it was 80 procent closed.
I told u guys that i didnt had any problems with the cowl removed , this is because the airfilter is seated on rubbers. and therefore it can move a bit with no cowl, resulting in a way less pinched hose.
Anyways thank you all that contributed.

Regards,
Dennis

 

[Spi D]

If you want to understand propellers, feel free to get the book

www.spidybot.com/prop_/Quicksilver_Propellers.pdf

Good to hear some was happy with a composite prop - I tried but couldn't see any other benefit than it's willingness to break if grounded. Definately did not perform anywhere near the original or the better after market makes