Mariner outboard motor fault

VicS said:
Isn't the engine in question just gravity fed ? I did not see any fuel pump on the parts diagrams!
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err well on the yam 4/5 its doesnt look like a pump its square about 1 1/2 inch by about 1/2 inch thick has 2 pieces of ... what looks like gasget material tho it must be more took me ages to work out what it was the coiled spring is About 3/4 inch very lite weight . I was told that the 4 and 5 only differed by carb and sttings mind you mine is about 99 so could have changed before 2003
 
ProDave said:
Okay, the motor's on the bench in a home rigged test tank.

Plug out and it looks fine, the gap was a little wide so closed up, but I don't think that's the problem.

Disconnected fuel line into carb, and fuel flows freely when fuel tap turned on, so not blocked tap / filter / air vent.

I can't see a drain plug in the bottom of the carb bowl. Anyone got a picture where I should be looking, or more detailed info on that.

I probably won't do much more today. Tomorrow I'll drain the fuel and put in a fresh mix. Yes it definitely says 100:1 on the motor. I'll use up the old a bit at a time in the lawnmower, that will run on anything and no cat to worry about. Saves the problem of otherwise disposing of it correctly.
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Diagram of carb here http://www.boats.net/parts/search/M.../0P017000 THRU 0P400999/Carburetor/parts.html

Dont be stingy with the oil in a 100:1 mix (I'd run 50:1 unless it oils up the plug) and be sure to fog it out at the end of the season or with next to no oil left in it you risk it seizing up.
 
fergie_mac66 said:
err well on the yam 4/5 its doesnt look like a pump its square about 1 1/2 inch by about 1/2 inch thick has 2 pieces of ... what looks like gasget material tho it must be more took me ages to work out what it was the coiled spring is About 3/4 inch very lite weight . I was told that the 4 and 5 only differed by carb and sttings mind you mine is about 99 so could have changed before 2003
Click to expand...

Yes you are right. It is part of the carburettor assembly. I was looking for a separate fuel pump
 
Very unlikely it's gravity fed. There is unlikely to be enough fuel head. If this is the same as the Tohastu/Mercury, which I think it is. The fuel pump is fitted to the side of the carburettor, it's a square block about 1/2 inch thick and works buy vacuum from the inlet manifold pressure changes on an internal diaphram.

Please bear in mind my earlier comments about the water level on the leg. If the engine is mounted too deep in the water this will gives exactly the problem you originally mentioned.
 
VicS said:
Isn't the engine in question just gravity fed ? I did not see any fuel pump on the parts diagrams!
Click to expand...

Mine had the diaphragm pump as described, presumably for some remote tank variant, with the built in tank, it just gravity fed, but there is a a little labyrinth of potential blockages and leaks.
I bought my Mariner 4, alias 'the ancient Mariner', second (fifth?) hand in about '94 so it was a previous generation.
 
fergie_mac66 said:
the drain is a screw right on the bottom of the carb usually has a small compressed coil spring on it. its a flat head screw probably slotted not pozi /philips about 5 mm dia it doesnt have to come all the way out
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Thanks, I've found it now. You remove a grommet in the outer case to gain access to it.

I was more thinking motorbike carbs and looking for a drain plug right on the bottom of the bowl, not on the side of it.

Yes this engine does have that square block pump thingy on the side of the carb.
 
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bonny said:
Very unlikely it's gravity fed. There is unlikely to be enough fuel head. If this is the same as the Tohastu/Mercury, which I think it is. The fuel pump is fitted to the side of the carburettor, it's a square block about 1/2 inch thick and works buy vacuum from the inlet manifold pressure changes on an internal diaphram.

Please bear in mind my earlier comments about the water level on the leg. If the engine is mounted too deep in the water this will gives exactly the problem you originally mentioned.
Click to expand...

I've always thought back pressure on the exhaust would make starting difficult, but less of a problem once it's running? (you can do the experiment with a moped....)
I suspect this is over-stated anyway, as one atmosphere is 10 metres of water?
Your description of the fuel pump is familiar.
If the engine is upright, and the tank full, there should be enough head to keep the float chamber full though.
Years ago, with a mate's motorbike, we ended up measuring the fuel flow with the float bowl off, he was getting fuel starvation at max power, due to a fuel filter. We worked out 20mpg (a guess) at 120mph in seconds to fill a litre jug IIRC.
 
ProDave said:
Thanks, I've found it now. You remove a grommet in the outer case to gain access to it.

I was more thinking motorbike carbs and looking for a drain plug right on the bottom of the bowl, not on the side of it.

Yes this engine does have that square block pump thingy on the side of the carb.
Click to expand...

If pump is blocked or failing it fiddly to put back together if you take it apart the diaphram is esily damaged and the 4 screw can be Bu@@ers to get out posi heads easily damage realy good proper fitting screw driver .....But only look at it as last resort!

EDit video it as you takeit apart so you can put it back together !!! if you can at least in your head !!
 
All sorted now.

I drained the suspect fuel into my lawnmowers can (having first emptied that into the motorbike) through the fuel tap with a length of hose. My suspicions were raised by the length of time it took to drain the tank.

There are two fuel filters. One is an in line plastic filter and that looked clear. But in the bottom of the fuel tap is a tiny bowl and a very basic gauze filter. Upon unscrewing this, it was found to be completely full of crud.

Having cleared it out, and re filled with freshly mixed fuel with fresh petrol, she started second pull.

I still wasn't happy with the idling and found I had to adjust the idle mixture screw to get it to idle properly. I's now been running in my test tank for about half an hour and I'm gradually getting back some confidence in it.

So where did this crud come from? Surely when the motor was serviced a few weeks ago they would have checked that? wouldn't they? So lets give them the benefit of the doubt and assume all this crud came from the suspect fuel I just put in. But that doesn't explain the idle setting wrong.

Long and short, I will only trust my own servicing from now on, at least I will know what has and has not been done.
 
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Sorry, but do you honestly think they checked that filter as part of the service? Very few people even know it exists and they don't block up that quickly unless the fuel you use is completely revolting. If they had cleaned it and serviced the engine correctly the idle speed would have been correct. Service it your self and as you have found you learn about the engine and can then get yourself out of trouble when there is nobody else to help.
Yoda
 
yoda said:
Service it your self and as you have found you learn about the engine and can then get yourself out of trouble when there is nobody else to help.
Yoda
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Couldn't agree more. Especially if you're capable.
Glad to hear you have found a problem and I hope all is now OK. Unfortunately running in a tank is one thing and on the boat is another - I've been there. It's not always practical to fully open the throttle in gear in a tank, it empties almost instantly.

Also if the engine has not been run for some time (or you don't know it's history) I would go easy at first and run it in (bore might be slightly rusty).

Good luck.
 
lw395 said:
I've always thought back pressure on the exhaust would make starting difficult, but less of a problem once it's running? (you can do the experiment with a moped....)
I suspect this is over-stated anyway, as one atmosphere is 10 metres of water?
Your description of the fuel pump is familiar.
If the engine is upright, and the tank full, there should be enough head to keep the float chamber full though.
Years ago, with a mate's motorbike, we ended up measuring the fuel flow with the float bowl off, he was getting fuel starvation at max power, due to a fuel filter. We worked out 20mpg (a guess) at 120mph in seconds to fill a litre jug IIRC.
Click to expand...

I think that I've recently experienced this effect of immersion depth affecting starting. It was with a Mariner 3.3 2-stroke. Absolutely refused to start when in usual running position with four aboard [18 ft. dayboat] but 2 days later started first time with just me aboard. My other Mariner 3.3 [used on the tender] is fine on the tender but always reluctant to start from hot when immersed in fresh water tank for rinsing after use so I'll try lowering level in tank. Remember that we're talking 2-strokes which feature dodgy simultaneous flows of incoming mixture and outgoing exhaust gases.
 
Just to finish this thread off by saying we took Ferndell out for the first time today in the inner Moray Firth.

The motor worked just fine, easilly cruising along at 5-6 knots on a modest throttle, and starting and running reliably.

We also got some sailing in, in glorious sunshine and light steady winds, perfect for us novices.
 
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When I had a Mariner 4 I used to get the the same symptoms from time to time. If it ran OK at idle but cut out as soon as any power was applied I always found it to be the main jet getting blocked. Taking the plate off covering the jets and cleaning it out was aways an immediate cure.
 
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