Outboard engine troubleshooting advise wanted (sorry, again..)

[TonD]

Hi all,

If you don't mind, I would very much appreciate some help with troubleshooting my 6 hp 2 stroke Mariner outboard. It's a 1997 model, don't have the exact model number present sorry.

We've had this engine for 2 seasons now and it has been running as great as can be expected. We've had it services every winter (new plugs, it's a two cylinder, new oil in the lower part and general cleaning and lubing). This season it's been acting up a little. Stalling more often which it never did before. Since last week, it's hard to start.

What I encountered is: starting just fine at first pull, then stalling after about 10-15 seconds. Hard/nigh impossible to restart. I removed the plugs, they looked in good condition (as they should after maybe 1,5 hours of use) but a little fouled. Not clean fuel, but black-ish soot. Anyway, removing them, cleaning properly and replacing did not instantly solve the problem.

On the fuel delivery part, we have an external tank that's slightly suspect. It's of the "NO NAME" variety and after this winter, the primer bulb had shrunk and seems less effective in actually priming the fuel line.

When, after trying and trying and trying, it almost started, it immediately stalled when I tried to rev it a little bit. This to me sounds like too little fuel (as I tried adding some more air made the engine stall).

What gives, should I replace the tank/primer bulb or look into fuel pump? I'm not new to engines in general (huge car guy) but have little to no experience at all with outboards. So rather than ripping off parts or replacing parts mindlessly, I'd greatly appreciate any good pointers

Thanks!

 

[TonD]

Sorry, guess I should've tried this first:
Borrowed a known to be working Quicksilver tank / fuel line / primer bulb combo with good fuel mixture in it. Primer bulb got firm after 1 or 2 squeezes and the engine fired right up. After switching back to original tank and making sure the primer bulb was pointing upwards when priming the line, everything was fine.

Lessons learnt:

1) Don't buy no-name primer bulbs (unless you want to replace every season).
2) Point primer bulb upwards when priming.

 

[TonD]

Sorry, guess I should've tried this first:
Borrowed a known to be working Quicksilver tank / fuel line / primer bulb combo with good fuel mixture in it. Primer bulb got firm after 1 or 2 squeezes and the engine fired right up. After switching back to original tank and making sure the primer bulb was pointing upwards when priming the line, everything was fine.

Lessons learnt:

1) Don't buy no-name primer bulbs (unless you want to replace every season).
2) Point primer bulb upwards when priming.

 

[Pete7]

Tony, how old is the fuel mix? anything mixed over a few months will have lost its zing and be difficult to start. Try replacing this first. Before you replace the fuel hose and bulb try leaving the cap unscrewed a little to see if the tank breather is blocked.

 

[oldharry]

First you need to establish whether fuel is getting to the engine. What can happen is that the non return valves in the bulb fail or leak stopping the engine from sucking fuel up. Try continuing to pump fuel up by hand once it starts. If you can keep it going then the bulb is at fault. Next you need to check the carburettor. The jets are quite small so that any water or dirt in the fuel will block them giving the kinds of problems you are experiencing. Aerosol carb cleaner is useful cleaning up. Try the choke in different positions to see if this makes any difference: if so the fault is a mucky carb. Check the engine pump is working. Disconnect the outlet pipe and with the plug spin the engine and see if you get a good flow of fuel. If not, suspect valves and diaphragms. Also check the feed pipe from the tank for splits and leaks.

Check also the 2 nuts holding the carb to the engine are not loose: an air leak here will throughly upset things.

This kind of fault can be very simple or the very devil to trace, so good luck!

 

[GrahamM376]

Good advice above. Also, check if there's a blocked filter in the remote tank. Some carbs have a drain screw under the float chamber and if yours has, remove it after the engine has stopped to see whether there's fuel or, if it has run dry.

 

[VicS]

First you need to establish whether fuel is getting to the engine. What can happen is that the non return valves in the bulb fail or leak stopping the engine from sucking fuel up. Try continuing to pump fuel up by hand once it starts. If you can keep it going then the bulb is at fault. Next you need to check the carburettor. The jets are quite small so that any water or dirt in the fuel will block them giving the kinds of problems you are experiencing. Aerosol carb cleaner is useful cleaning up. Try the choke in different positions to see if this makes any difference: if so the fault is a mucky carb. Check the engine pump is working. Disconnect the outlet pipe and with the plug spin the engine and see if you get a good flow of fuel. If not, suspect valves and diaphragms. Also check the feed pipe from the tank for splits and leaks.

Check also the 2 nuts holding the carb to the engine are not loose: an air leak here will throughly upset things.

This kind of fault can be very simple or the very devil to trace, so good luck!

Can you do this on the engine in question? Isn't the fuel pump integral with the carb?

 

[VicS]

Hi all,

If you don't mind, I would very much appreciate some help with troubleshooting my 6 hp 2 stroke Mariner outboard. It's a 1997 model, don't have the exact model number present sorry.

I'd greatly appreciate any good pointers

Thanks!

Start with a compression test. Should be 115 -125 psi ( min 100psi) and the two cyls within 15% of each other.

Check sparks preferably with a spark tester Not just with the plugs.

Clean plugs and set gap (NGK BP8HS-10 I believe gapped at 0.040" / 1.0mm) If any doubt bout them replace.

Flush out fuel tank if suspect and check fuel filter.

Using fresh fuel mix (50:1 with a TCW3 oil) check that you get a good flow when squeezing the bulb with the hose between the filter and the fuel pump/carb disconnected.

Reconnect fuel hose , prime the carb bowl. You should feel the bulb go firm when the bowl is full. See if you can start it following the specified cold start procedure. If it wont start and run see the workshop manual regarding the primer system. If you can start it and can keep it running by squeezing the ball suspect air in leak at the fuel line connector or a defective fuel pump.

If you can keep it running by operating the primer pump( choke) suspect the need for a carb clean


Workshop manual at http://boatinfo.no/lib/mercury/manuals/6-8-99-10-15.html#/

 

[dod]

all sound advice above but IMO at little too technical for the OP As this is a 2 stroke the fuel mix is important so make sure it is correct then find out where the main fuel jet is in the carb and make sure it is clear as with the float jet. use matchstick or wooden cocktail stick to clear jets Also think you need to change your fuel lines and clean out the tank.
there you go sorted.

 

[seaangler23]

Likely fueling but check the throttle linkages, I sorted a 8hp one of that kind of age and it had a fairly complicated throttle linkage set up and the ignition advance and retard arm wasn't shifting, a good clean up and greasing sorted it

 

[lydiamight]

Upon the recommendation of my local Garden Machinery suppliers I have taken to using this http://briggsandstrattonparts.co.uk/briggs-and-stratton-fuel-fit-992381/
It is supposed to stabilise the fuel for up to 36 months and prevent "gumming" of carbs. Seems to get pretty good reviews. Only time will tell if it is "snake oil" but for a modest expenditure it is probably worth trying.

 

[TonD]

Thanks for all the sound advice!

I went to the boat last night, equipped with a borrowed Quicksilver tank / fuel line / primer bulb / fuel-mixture set known to be working just fine on another 5hp Mercury 2 stroke.

Sure enough, after 1 to 2 squeezes of the primer bulb it became firm. Started the engine after one pull and it kept running. I disconnected the fuel line to let it stall from running out of fuel.

Re-attached my own tank and -what I had learnt from Googling and did not know before - as I held the primer bulb pointing upwards to help the no-return valve it became firm after a few squeezes as well. Fired up and kept running.

Just to be sure I took out spark plugs again, they were dirtier than I expected: cleaned them an hour (of running time) before and again quite black/sooty/carbon and one the top most cylinder a bit of oil. Then again, I'm used to looking at plugs from 4 stroke modern car engines so can't really compare. Anyway, to me seems the mixture might be too rich?

I also re-tightened some bolts holding, hoping to prevent some unwanted leaks.

All in all I think I'll replace the primer bulb with an original Quicksilver/Mercury/Mariner one, as the one I have now died on me in less than two years. I'll also look into using better 2 stroke oil and perhaps the mixture.

Thanks!

 

[VicS]

Thanks for all the sound advice!

I went to the boat last night, equipped with a borrowed Quicksilver tank / fuel line / primer bulb / fuel-mixture set known to be working just fine on another 5hp Mercury 2 stroke.

Sure enough, after 1 to 2 squeezes of the primer bulb it became firm. Started the engine after one pull and it kept running. I disconnected the fuel line to let it stall from running out of fuel.

Re-attached my own tank and -what I had learnt from Googling and did not know before - as I held the primer bulb pointing upwards to help the no-return valve it became firm after a few squeezes as well. Fired up and kept running.

Just to be sure I took out spark plugs again, they were dirtier than I expected: cleaned them an hour (of running time) before and again quite black/sooty/carbon and one the top most cylinder a bit of oil. Then again, I'm used to looking at plugs from 4 stroke modern car engines so can't really compare. Anyway, to me seems the mixture might be too rich?

I also re-tightened some bolts holding, hoping to prevent some unwanted leaks.

All in all I think I'll replace the primer bulb with an original Quicksilver/Mercury/Mariner one, as the one I have now died on me in less than two years. I'll also look into using better 2 stroke oil and perhaps the mixture.

Thanks!

It does sound from the appearance of the plugs that you might be running rich , or the carb is flooding slightly if they become sooted or oiled up in a n hour of running at speed but you cannot tell just idling in a tank or on muffs. A good run at WOT is needed
There should be enough info in the manual I gave the link to to check/ adjust/ remedy as necessary to enable you to sort it out.

Sorry I should have suggested pointing the bulb at the sky. I do it without thinking about it!

 

[tudorsailor]

I had a problem with the carb being gummed up on my 4HP Yamaha. Since I have never cleaned a carb I got a (greek) mechanic to do it while I watched. He suggested that I get an inline filter to stop the dirt getting to the engine. I always use an external tank, and have hose with bulb. I did buy a little in line filter, but could not see how I could arrange things so that it always full of fuel but with no air. Are they suitable for my set up without any permanent fixture to the dinghy?
TudorSailor

 

[VicS]

I had a problem with the carb being gummed up on my 4HP Yamaha. Since I have never cleaned a carb I got a (greek) mechanic to do it while I watched. He suggested that I get an inline filter to stop the dirt getting to the engine. I always use an external tank, and have hose with bulb. I did buy a little in line filter, but could not see how I could arrange things so that it always full of fuel but with no air. Are they suitable for my set up without any permanent fixture to the dinghy?
TudorSailor

I dont think I would attempt to fit a filter like that in the fuel line. I would try to fit it under the cowl somewhere

6 hp, and other larger engines, do in fact have similar filter fitted between the fuel line connector and the fuel pump/carb assembly

Yamaha part number 646-24251-02-00 Sorry abut the size of the image . It's actually less than 2" long overall

 

[pagoda]

Tony, how old is the fuel mix? anything mixed over a few months will have lost its zing and be difficult to start. Try replacing this first. Before you replace the fuel hose and bulb try leaving the cap unscrewed a little to see if the tank breather is blocked.

Absolutely +1. Last year's 2 stroke mix is generally less willing to ignite in my experience. I have also adopted the "run in neutral until it stops" method. That empties the float chamber and reduces the chance of gumming up.
Breathers are things most people don't think deeply about, but an outboard will not draw fuel properly unless the breather is open. (for what it's worth- some classic cars have had tanks collapse due to incorrect "no breather" tank caps!)
Tank cleanliness is a pretty worthwhile target. Better than misfiring/ stuck half a mile from your boat!