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8hp 2 stroke mariner awkward to start and pumps weak and hot water

R

Ruan Urquhart

New member
Hello,
I recently aquired a mariner 8hp outboard and have been having troubles with it.

In order to start it you must give it some throttle, however there is a mechanism that prevents you from giving it any throttle when in neutral, so you must put it in gear, but when you put it in gear it locks the pull cord, so you must take of the hoode, disconnect a rod, give it some throttle and pull it many times at varying throttle positions, and once it starts you then need to throw it into neutral again otherwise it creates a lot of wash in the bin that it is sat in, where it often cuts out because you cant give it any revs. I have been running it in a large wheelie bin but even after a few seconds running the water from the tell tale ( which is a very weak spluttery flow ) begins to heat up very quickly. Not scaldingly hot, but definatelly too hot.

So far i hate this outboard compared to every other one I have ever owned. You cant start it in gear without taking the hood of and disconecting thing, you cant give it any throttle in neutral, and there is a twisty dial sat beside the tiller that is for adjusting the idle speed i believe and it can also be pulled out to turn the choke on. Why can the idle setting dial be somewhere hidden where you arent likely to adjust it be accident?

So in short could somebody please give suggestions on how to get it to start without needing any throttle, and as to why the pee streem gets hot very quickly and has a weak flow? ( although im guessing a bad impeller for the weak stream part )

Thanks for your time,

Ruan
 
These are great little motors.

Before you kill it service the water pump and clean the carb.

They should start and idle "perfectly" without needing any throttle. Also, if you don't know the history back up a little further.


Check the compression - 90 psi or better in both cylinders is what you are looking for.

If that's ok, check for spark with a timing light or spark tester.

While you are doing the water pump and besides the impeller there is a couple of other seals there (rubber) that cost about 5 bucks each and should be changed, also drain, check and refill the lower unit with gear oil.

Replace the sparkplugs - again, they are relatively cheap and probably need changing.

Not much else goes wrong with these motors. They do develop cracks in the coils with age requiring replacement, they are also hard on main seals when they get on in years.

Merc stopped building this model for the US market back in 2005 and the export models have been out of production for a couple of years now. They were first built in 1986 so you could have a model that is anywhere from 28 years old to maybe 10.

If you really don't like the throttle/shift all in one, sell the motor. They were popular (and continue to be) and pick up an OMC.
 
galamb said:
These are great little motors.

Before you kill it service the water pump and clean the carb.

They should start and idle "perfectly" without needing any throttle. Also, if you don't know the history back up a little further.


Check the compression - 90 psi or better in both cylinders is what you are looking for.

If that's ok, check for spark with a timing light or spark tester.

While you are doing the water pump and besides the impeller there is a couple of other seals there (rubber) that cost about 5 bucks each and should be changed, also drain, check and refill the lower unit with gear oil.

Replace the sparkplugs - again, they are relatively cheap and probably need changing.

Not much else goes wrong with these motors. They do develop cracks in the coils with age requiring replacement, they are also hard on main seals when they get on in years.

Merc stopped building this model for the US market back in 2005 and the export models have been out of production for a couple of years now. They were first built in 1986 so you could have a model that is anywhere from 28 years old to maybe 10.

If you really don't like the throttle/shift all in one, sell the motor. They were popular (and continue to be) and pick up an OMC.
Click to expand...

Thanks for that mate!
So I've decided I would start with the simple things and begin by getting new sparkplugs. I have however just noticed after removing them that the outboard had two different spark plugs in it, one being slightly longer than the other! ( by a few threads ) Do you know what the correct sparkplug is that i should get or it? Currently it has a "CHAMPION J8C" and a "NGK B7HS" so I dont know which one ( if any ) is the correct one i should be purchasing more of.

Thanks for your time,

Ruan
 
Neither plug is correct - first off, only use NGK or Autolite in these Mercs - Champions don't have the correct resistance (even if the cross ref says they will work).

The correct plug is an NGK BP8-N-10 gapped at .040". Those should make a difference to start with.
 
galamb said:
Neither plug is correct - first off, only use NGK or Autolite in these Mercs - Champions don't have the correct resistance (even if the cross ref says they will work).

The correct plug is an NGK BP8-N-10 gapped at .040". Those should make a difference to start with.
Click to expand...

Thank you Kindly mate :)
 
Those are listed wrong - according to the NGK website, that plug is for 4 and 5 horse motors - not the 6/8.

From the NGK selector - NGK 4838 BP8H-N-10 Nickel

 
That's them. At what 4 1/2 pounds each I might install oars :)

I buy them by the dozen for 20 Canadian dollars which is right about 9 BP)...
 
galamb said:
That's them. At what 4 1/2 pounds each I might install oars :)

I buy them by the dozen for 20 Canadian dollars which is right about 9 BP)...
Click to expand...

Haha unfortunatly some things are a little pricey over here in the uk. 1 litre of petrol/gas = around $2.50 canadian dollar :p
So since you buy them by the dozen does this mean you do a lot of work on this paticular outboard, or where you just talking about sparkplugs in general that you buy? :)
 
I work mostly on Merc's and generally don't work on anything over 25 horses (and don't touch the 4 strokes).

So I usually keep a dozen pack of BP8HN 10's and BP8HS 15's - that covers everything from 6 thru 25 horse (Merc and Merc Mariner) that was built from 1986 up until the last ones came off the line in 2012.

I have a pair of 9.9's and a 15 horse and use them quite a bit. I consider changing the plugs an annual event just like changing the gear oil. Many would say that's a waste, but I have never had an issue with the ignition preventing it from running, save one occasion when a coil toasted on me.

Changing plugs annually when you get them for under 2 bucks a plug - a few bucks a year. Never getting stranded on the lake - priceless :)
 
galamb said:
I work mostly on Merc's and generally don't work on anything over 25 horses (and don't touch the 4 strokes).

So I usually keep a dozen pack of BP8HN 10's and BP8HS 15's - that covers everything from 6 thru 25 horse (Merc and Merc Mariner) that was built from 1986 up until the last ones came off the line in 2012.

I have a pair of 9.9's and a 15 horse and use them quite a bit. I consider changing the plugs an annual event just like changing the gear oil. Many would say that's a waste, but I have never had an issue with the ignition preventing it from running, save one occasion when a coil toasted on me.

Changing plugs annually when you get them for under 2 bucks a plug - a few bucks a year. Never getting stranded on the lake - priceless :)
Click to expand...

I agree about changing plus annually, even if the old ones are fine. We go fishing in Loch Ewe, a relatively large sea Loch in Scotland. If your outboard broke down and the currents were too strong to row against then you'll be drifting out the loch into open sea before you know it. Thankfully I have an Uncle who has gifted us a mariner 4hp which can be used as an Auxillary :)

So my plugs arrived today and i've gone ahead and fitted them. The only thing is I didnt take notice of which HT lead goes to which sparkplug! Would I be right in saying that the right hand side lead is for the lower sparkplug?

IMG_20140724_142149097_zpsbmdgvjzk.jpg


Thanks!

After this I'll clean out the carb and then order a new impeller along with all the required seals.

Thanks again,

Ruan
 
Yes, right hand coil, as you are looking at the back of the motor feeds the bottom.

The coil with the green/yellow wire is top (cyl 1) and green/white feed is for cyl 2 (bottom)
 
galamb said:
Yes, right hand coil, as you are looking at the back of the motor feeds the bottom.

The coil with the green/yellow wire is top (cyl 1) and green/white feed is for cyl 2 (bottom)
Click to expand...

Hi mate,

Good news; After cleaning out the carb and replacing the spark plugs the outboard started first pull. Also seemed to idle well however still spluttered water and the water got hot very fast. Despite a "friend" telling me that outboards dont have thermostats, I removed the thermostat cover to find ( much to his suprise ) a thermostat! I placed it in boiling water and it seemed to open ok, so no problems there, but i thought id run the outboard without it for few minutes to see if it made a difference to the flow of water coming from the tell-tale, and boy it sure did! Moments after starting a very solid stream of water flowed out with a good force behind it, and it stayed at a cool/warm temperature getting no where near as hot as it did with the thermostat in.

Looks like ( for now ) I wont be needing an impeller. Although i will replace it at the end of the season for good measure, along with all the corresponding seals. All thats left now is to get our boat in the water and mix up some fresh fuel/oil- which leads me to my next question. Do you know the correct fuel to oil ratio that i should be using?

Thanks for your time and help mate,

Ruan
 
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