What's wrong with my Mariner 4 2 stroke OB

[ProDave]

It seems to be deteriorating.

Starts fine.

Runs under load fine.

When running under light load (i.e low revs) it runs fine most of the time, but occasionally the revs will drop and it will sound rough, then go back to normal. Reading other threads I think this may be "4 stroking"

today returning into the harbour, it now does not like running at very low revs. To spite me it died completely as I was approaching the harbour wall (thankfully not a big problem today)

so I did some investigating when safely tied up.

It will start and run at idle, but sounds rough, like it's misfiring (is this the 4 stroking thing, only firing half as often as it should)?

Give it moderate power, and it will run for a bit then slowly die and stall (that's what happened pottering in at very low revs)

It's not a fuel starvation issue as it's fine at high revs / power.

I changed the plug for a new one, no difference.

I guess it's a carburettor issue. Don't just say "clean the jets" as I wouldn't know which one and how. I need a but more help than that.

I should add cooling seems fine, it's peeing nicely, and the water from the pee hole is barely tepid, so it's not overheating.

 

[lustyd]

No need to clean the jets, you might want to adjust the two screws on the carb. That's what fixed it for mine along with a new fuel pipe to the external tank. Someone else can explain better but basically one of the screws you screw in slowly until in all the way then back off until the engine over fuels (too rich). Mark this position and screw back in until it under fuels (too lean). Half way between these is right, err on the side of too rich.
This may not be it but it sounds like what mine did.

It seems to be deteriorating.

Starts fine.

Runs under load fine.

When running under light load (i.e low revs) it runs fine most of the time, but occasionally the revs will drop and it will sound rough, then go back to normal. Reading other threads I think this may be "4 stroking"

today returning into the harbour, it now does not like running at very low revs. To spite me it died completely as I was approaching the harbour wall (thankfully not a big problem today)

so I did some investigating when safely tied up.

It will start and run at idle, but sounds rough, like it's misfiring (is this the 4 stroking thing, only firing half as often as it should)?

Give it moderate power, and it will run for a bit then slowly die and stall (that's what happened pottering in at very low revs)

It's not a fuel starvation issue as it's fine at high revs / power.

I changed the plug for a new one, no difference.

I guess it's a carburettor issue. Don't just say "clean the jets" as I wouldn't know which one and how. I need a but more help than that.

I should add cooling seems fine, it's peeing nicely, and the water from the pee hole is barely tepid, so it's not overheating.

 

[forelle541]

I had a force OB that did this, at the boat show a tech told me to take the carb apart and clean it out and polish the inside, sounds a faf but it worked, small two strokes only take a small amount of gum to upset them.

 

[ProDave]

I had a quick look. there was one obvious screw on the top surface of the carb. the only other adjustment was a stop screw on the throttle linkage (slow running speed?)

So just how do you determine the "too lean" or "too rich"?

 

[VicS]

It does sound as though it needs a thorough carb clean although 4 stroking is sign of running too rich ...... so try screwing in the mixture screw a litlle.

You dont say what model exactly but you should be able to find an exploded parts diagram at http://www.boats.net/parts/search/Merc2/Mariner/parts.html

remove and take apart carefully watching out for small parts and noting how they were all assembled. Note the setting of adjustment screws so that you can get them at least roughly right as you rebuild it.
(Look out for a little clip between the float arm and the needle valve)

Clean all jets nozzles and passage ways. Soft copper wire ( strand of electric wire) is useful for poking through jets without causing damage

A repair kit might be worth considering but cheap they are not!

 

[ProDave]

If it needs a full strip down It will have to wait a few weeks until the boat is out. too much faff to get it off and risk breaking it altogether leaving the boat engineless.

I've never had much luck with stripping carbs before (lawnmowers etc) so does anyone know someone in the Inverness area that will do it for me for a fair price (Don't suggest Calley please)

 

[davidpbo]

Take a look at my recent post on my Mercury 8HP.

Symptoms were it ran reasonably high revs but was prone to cutting out etc. at low speeds. Approaching jetties, moorings etc at ramming speed or dead engine was not without its excitement.

I have not picked it up yet to ascertain that the problem is solved but am told it is running well. It would appear it was a crankcase seal (lower). The recommended mechanic had only experienced this fault once a long time ago and was flummoxed as to what the problem was.

http://www.ybw.com/forums/showthread.php?360622-Mercury-8-HP-CC-1988-2-Stroke-problems-Long-post&highlight=

 

[boguing]

'Could' also be a little bit of water in the system.

With these symptoms I'd just take the carb off and apart, quick clean with petrol and reassemble. To do it properly I'd drain the tank, fit a new petrol filter and put the previously drained petrol back in whilst watching through a clear pipe for water (heavy) in the last quarter of it.

 

[sunquest]

It does sound as though it needs a thorough carb clean although 4 stroking is sign of running too rich ...... so try screwing in the mixture screw a litlle.

You dont say what model exactly but you should be able to find an exploded parts diagram at http://www.boats.net/parts/search/Merc2/Mariner/parts.html

remove and take apart carefully watching out for small parts and noting how they were all assembled. Note the setting of adjustment screws so that you can get them at least roughly right as you rebuild it.
(Look out for a little clip between the float arm and the needle valve)

Clean all jets nozzles and passage ways. Soft copper wire ( strand of electric wire) is useful for poking through jets without causing damage

A repair kit might be worth considering but cheap they are not!

Yup around £60. I had similar symptoms with a 2004 Mariner 15 HP. Turned out to be the choke valve at the bottom of the carb. It is unlikely to be the jets if there is an in line fuel filter!

 

[cliff]

I had a force OB that did this, at the boat show a tech told me to take the carb apart and clean it out and polish the inside, sounds a faf but it worked, small two strokes only take a small amount of gum to upset them.

+1 - good cleaning and new spark plug - first step in solving the puzzle

Take a look at my recent post on my Mercury 8HP.

Symptoms were it ran reasonably high revs but was prone to cutting out etc. at low speeds. Approaching jetties, moorings etc at ramming speed or dead engine was not without its excitement.

I have not picked it up yet to ascertain that the problem is solved but am told it is running well. It would appear it was a crankcase seal (lower). The recommended mechanic had only experienced this fault once a long time ago and was flummoxed as to what the problem was.

http://www.ybw.com/forums/showthread.php?360622-Mercury-8-HP-CC-1988-2-Stroke-problems-Long-post&highlight=

Different carb. - I would still go for a good cleaning etc before going down the replace seals route.

'Could' also be a little bit of water in the system.

With these symptoms I'd just take the carb off and apart, quick clean with petrol and reassemble. To do it properly I'd drain the tank, fit a new petrol filter and put the previously drained petrol back in whilst watching through a clear pipe for water (heavy) in the last quarter of it.

Drain the float bowl. Any water come out? no? then clean the carb - oops clean the carb anyway with carb cleaner - petrol will not remove the gummy deposit

Yup around £60. I had similar symptoms with a 2004 Mariner 15 HP. Turned out to be the choke valve at the bottom of the carb. It is unlikely to be the jets if there is an in line fuel filter!

I did not know an in-line fue filter would stop the gummy deposits forming . I know they help stop bits of dirt and grit etc getting to the carb but you say they also prevent the gummy deposit left when petrol evaporates? wow

 

[lustyd]

+1 - good cleaning and new spark plug - first step in solving the puzzleDifferent carb. - I would still go for a good cleaning etc before going down the replace seals route.Drain the float bowl. Any water come out? no? then clean the carb - oops clean the carb anyway with carb cleaner - petrol will not remove the gummy depositI did not know an in-line fue filter would stop the gummy deposits forming . I know they help stop bits of dirt and grit etc getting to the carb but you say they also prevent the gummy deposit left when petrol evaporates? wow

In 3 years I've never had these gummy deposits in mine. I suspect it's partly because I allow the engine to run dry before I leave it, and partly because I don't put extra oil in "just in case". I'm not saying the carb doesn't need cleaning, just that the forum always seems to think this solves everything and it definitely doesn't.

 

[smithy]

Have had similar symptoms with mine from time to time. Usually turns out to be some water lying in the bottom of the carb. Wouldn't start playing about with adjustments until you clear the float bowl out, its unlikely that they will have moved.
Take the carb off, turn upside down over container and remove the bottom. Often you will see a tiny amount of water in the petrol that runs out. Some carbs have a drain screw in the bottom which makes life easier but not always the case. Its really not that difficult. If that doesn't do it, as others have said strip and soak all parts in carb cleaner then blow through with compressed air.

 

[FishyInverness]

I've never had much luck with stripping carbs before (lawnmowers etc) so does anyone know someone in the Inverness area that will do it for me for a fair price (Don't suggest Calley please)

You could always give us a call Dave, and speak with Jim, our outboard Mechanic. Couldn't say what he'll quote you, but the price of a phone call should find it out

Alternatively Jeff at Sunsun engineering out at Hopeman might be worth a shout,, I know he takes on all sorts of little outboard jobs and is fairly regularly around Inverness.

 

[ProDave]

Yes I might well do that Fishy.

All I know is I had bad experiences with your main competitor further along the Calley, so don't want it to go there.

I'm in a bit of a dilemma. There's realistically only a few weeks left of this season (don't yet know the clubs crane out dates)

So do I carry on knowing it's unreliable? If I do I'll keep the hook handy in case things go pear shaped on the way into the harbour.

Or do I take it off the boat and get it fixed now?

I don't think stripping the carb is something I would try with it hanging off the back of the boat.

 

[davidpbo]

Stripping the carb on the back of the boat isn't something you want to try. I do take my carb off with the ob mounted in a well but that is a relatively simple procedure, I do try to block any places bits might fall through or into.

Fuel filters do not IMHO stop all carb blockages. I always run the engine with the fuel tap off at the end of each use but still had a lot of foam type goo in the float chamber once. Thinking about it, turning the tap off or disconnecting a fuel line probably won't run the carb completely dry as draining it might. There is a drain screw on my 3.5 Tohatsu but not on the main boat engine which despite the troubles I have had recently had never had any gunge in the float bowl when stripped. That engine I do run as dry as possible by disconnecting the fuel line but that still (I think) leaves reservoir of fuel in the fuel filter on the engine and
presumably in the float chamber.

P.S I have the 8hp mercury back and it seems much better although it did cut out running at low revs as I was coming into the jetty. The revs also increased and decreased sometimes whilst we were motoring.

 

[Lakesailor]

It would appear it was a crankcase seal (lower). The recommended mechanic had only experienced this fault once a long time ago and was flummoxed as to what the problem was.

I would have expected poor starting if the crankshaft seal wa that bad.
Have you changed the fuel filter? Cheap and easy first move with erratic running. It's surprising how often this is the problem.

 

[macd]

P.S I have the 8hp mercury back and it seems much better although it did cut out running at low revs as I was coming into the jetty. The revs also increased and decreased sometimes whilst we were motoring.

Are you saying these symptoms are from before the Mercury was fixed or after? I hope the former.

The 'up and down' revs regardless of throttle position are classic symptoms of a leaking crankcase seal on a two-stroke. The leak allows air to bleed into the crankcase and thence into the cylinder; since it tends to be erratic, the revs will rise and fall of their own accord. As Seajet says, it often also causes poor starting. This is always a fault that should be addressed immediately, as the engine will run weak (due to the excess air leaking in): overheating and a holed piston are right around the corner.

 

[lw395]

The only two stroke I have had the crank seals fail on was very hard to start.
Before suspecting that, I would suspect a small drop of water in a jet part of the time.

There is a screw on the bottom of the carb.
You should be able to undo this while the carb is on the engine, IIRC by removing rubber bung in the base of the cowling.
Slacken screw and catch all that comes out in a jam jar.
Best to let the motor stand for a few minutes first.
Inspect for water.
The water need not get in through the fuel filter, it forms as condensation in the carb.
Some of it ends up in the float bowl.
Find a spare screw or two that fits, they don't float.
It may have a fibre washer on it.
Allen screws are easiest to put back, keep a key in the toolkit or even under the cowling.
I had this a lot while keeping my ob in a damp shed at the club.

A shop that deals with mopeds might clean the carb for you?
Personally, I would not be happy going afloat and relying on a motor if I did not have the tools and knowledge to clean the carb.
It's not hard.
At least to get the float bowl off.
You need a clean space and a bit of A3 white paper to work on, plus a few small tools.
IMHO, that float bowl wants to come off every time the motor farts out of tune.
Also, buy it a new plug. NGK are the best for 2 strokes.

 

[davidpbo]

Are you saying these symptoms are from before the Mercury was fixed or after? I hope the former.

It was after. We will see if I have continuing significant problems.

I have had a problem with the fuel hose coming unclipped and when I investigated this morning it was off, new connector needed as it seems to happen a little too regularly. The engine is greatly improved but may be in need of a tweek to mixture working under load rather than in a tank.

I did ask about replacing all the crankcase seals but was dissuaded by the mechanic who came highly recommended.

 

[deuc02]

Strip and clean the carb. V easy and will probably cure. As for repair kits - complete waste of money.