Outboard running slow

[sailboatliving]

I got a mariner 9.9 HP outboard, 2 stroke, on my dinghy and now it runs slow like a 2 HP. It doesn't misfire and runs very smoothly. It starts on first attempt with choke and everything else seems fine. Idle RPM is low, but not low enough for it to stop. RPM used to be pretty high when it worked better.

I have tried to pull the throttle manual under the hood and it doesn't increase the speed. I think one coil is broken or bad but I can't get a new where I'm at. I would think bad fuel or fuel line issue would cause other symptoms as well, like running erratic,. misfiring. But mine is running smoothly, just extremely slow. Top speed is probably 2-3 knots right now. Fuel is 1 month old from a gasoline station.

I have 2% oil in the gasoline and I bought it from a gasoline station 2 months ago.

Spraying with carburetor cleaner didn't change anything.

I DON'T have any of these symptoms:
difficulty starting, rough idling, sputtering, jerky acceleration, and occasional backfires



Anyone knows what I can check and fix?

 

[billskip]

At a guess it's a blocked jet...but you think it's the coil..easy coil test is start it and pull off a plug lead, if it stops/changes then try the other one, if it stops/changes it's not the coil.

 

[wallacebob]

“Spraying with carb cleaner” ? Cleaning the carb requires dismantling, I think blocked main jet. Short cut is to disconnect fuel line and spray cleaner in bowl directly.

 

[thinwater]

If it has been running on e10 the blockage is likely from aluminum corrosion products. A cleaner won't dissolve it. You will need to poke out the jet with a fine wire, perhaps plucked from a small wire brush.

To prevent recurance ...

• Keep the gas dry. Keep the vent closed when not running.
• Use an anti-corrosion additive. Biobor EB should be available in the UK. Most gas additivs are either snake oil or they are for non-ethalon gas, which is different. This one has done well in both PBO and PS testing.

Living with Ethanol. Good Old Boat.

 

[KevinV]

....now it runs slow...

I always start by asking "what has changed?" and working back from that. Has it been stood? Dropped? Change in fuel? Serviced? Run very hard?

Start with some fresh fuel - I've had dodgy batches from fuel stations at times, especially in remote locations - it happens.

FWIW I don't use steel wire to poke out jets, especially tiny ones where the margin of error is smaller. Copper is gentler and comes in a variety of sizes thanks to various bits of cable on board

 

[VicS]

MY first guess would be that it is not firing on one cylinder therefore check as billskip suggests but use insulated pliers or heavy rubber gloves to pull off the plug leads or you are likely to get one hell of an electric shock,

If this gives a positive result ( ie pulling off one has no effect while the pulling off the other stops it dead) it could be a faulty spark plug or a faulty coil ( there are two coils , one for each cylinder, not just one as implied a couple of times in the answers so far )

If pulling off the plug leads one at at time has no effect then divert your attention to the carb first checking that the throttle valve is in fact opening fully

Re cleaning the carb I agree spraying carb cleaner into it is not likely to have any beneficial effect. It'll need to be dismantled and cleaned thoroughly, poking through the jets with a soft copper wire.

 

[sailboatliving]

Thanks for the responses. I will check coil and carburetor jet. I just did it 2 months ago though.

It was running normal when I went to the dinghy dock, I sprayed it with water with case on and when I came back it ran slow

 

[billskip]

or you are likely to get one hell of an electric shock,

He'll know the coil is ok then...
Could be a plug, also could be the drive end like fishing line round the prop area causing it to stall, normally you would notice something even sound difference if throttle was opening...maybe even the advance mechanism link come adrift....
Does it rev out of gear?...could be water pump impeller mangled causing stall....
But I still go for carburetor problem .

 

[thinwater]

Thanks for the responses. I will check coil and carburetor jet. I just did it 2 months ago though.

It was running normal when I went to the dinghy dock, I sprayed it with water with case on and when I came back it ran slow

If it is ethanol gas, water in the fuel will do that. Just 0.5% water is enough to make the ethanol phase separate, and the water/ethanol phase is 90% ethanol and will run ... slow. I've had that happen after a rainstorm. The cure was pump the bottom of the tank, add some fresh fuel, and change the filter.

Phase separation in new to the UK. We learned about that in the US 29 years ago (1995 EPA memo below). The solution is to keep the gas very dry. The other difference is that e10 with even 0.1% water becomes a weak electrolyte, promoting galvanic corrosion. Keep it dry and use a corrosion inhibitor.

EPA memo phase separation E10

 

[billskip]

, I sprayed it with water with case on and when I came back it ran slow

Well that could cause enough moisture/damp on the ignition system to
cause your problem...let it completely dry out in the warm if possible and buy some (dampstart ?) Electrical Water proofing spray (don't spray it in the carb) spray it on all the electrical stuff.

 

[sailboatliving]

The carburetor jet was not the problem. I cleaned it and no difference.

But one coil or at least the cable between the coil and the spark plug has no connectivity. I ran it with the good coil and spark plug and it ran like it has the last few days, slow but stable.

 

[Egret]

Can stale petrol be cleaned/filtered or is it just dead - and can it be mixed with fresh petrol or will the gummy parts just clog the jets particularly in a small 2.5hp 4 stroke outboard

 

[thinwater]

Can stale petrol be cleaned/filtered or is it just dead - and can it be mixed with fresh petrol or will the gummy parts just clog the jets particularly in a small 2.5hp 4 stroke outboard

There is a long technical answer, but the short answer is no. I assume there is a citizen disposal system.

 

[Boathook]

The carburetor jet was not the problem. I cleaned it and no difference.

But one coil or at least the cable between the coil and the spark plug has no connectivity. I ran it with the good coil and spark plug and it ran like it has the last few days, slow but stable.

So it seems like the coil / lead is faulty ? Normally they are sealed units so will need to obtain a 'new' one.

 

[billskip]

So it seems like the coil / lead is faulty ? Normally they are sealed units so will need to obtain a 'new' one.

I think I'd try the plug first....

 

[sailboatliving]

Yeah, there is no connectivity in the coil and the same with the cable

So it seems like the coil / lead is faulty ? Normally they are sealed units so will need to obtain a 'new' one.

Yeah, there is no connectivity when I checked with a multimeter in the coil and the same with the cable