Yamaha 8 2-stroke Outboard not starting

[MondayNever]

Hi all,
I've got a 3-4 year old Yamaha 8c 2-stroke outboard. Up until today it had been starting in 1 or 2 pulls almost every single time. Today I drove it around on three occasions, then literally 5 minutes after I had stopped it after a quarter mile trip, she failed to start. Lots more cranking, no bueno.

I pulled the plugs and they looked rather sooty but totally dry, which suggests to me that she wasn't flooded. Pulled the starter a few times to be sure that the cylinders were clear then reinstalled a set of old plugs that worked when I swapped them out a few months ago. Also checked to make sure that both plugs were sparking, which they seemed to be as best as I could tell in full sunlight (finger jolt).

Pulled the little disposable inline filter and it looked clear. Also squeezed the bulb with filter removed from the engine side and it squirted fuel.

So.. fuel is at least arriving at the carb, spark plugs are sparking, pull start cranks it as fast as ever... what next? I don't know a thing about rebuilding/cleaning carbs, so hopefully you'll have another suggestion.

The only thing I can think of that was different about today was that I just filled up with a fresh tank of gas. I added oil, but only sloshed the tank around a little before taking off. I assume that I wouldn't be able to pull the starter if the pistons were siezed, though.

Any thoughts are welcome. Sailing out of Grenada tomorrow and would love to not have to row everywhere.

[44'cruisingcat]

If you've been cranking a lot with the choke on, you'd expect the plugs to be a little wet.


Could be a blockage in the carb?


You could try dribbling a little fuel into the spark plug holes, refitting the plugs and try again?


If it fires then stops, that would suggest there's a fuel blockage. If it doesn't fire, it's more likely ignition.

[Reefmagnet]

Blocked carby jets or water the the bowl. Drain the bowl via the screw at the bottom of the carby and see what comes out. If still no luck clean the carby jets. Not as daunting a task as it sounds if you haven't done it before.

[ben373]

+1 for water in carby

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[MondayNever]

Pulled the carb last night and cleaned it as best as I could. Couldn't remove one of the jets due to not having a screwdriver that would fit, but soaked that area in acetone. Reassembled and still nothing. Lots of cranking but plugs stayed pretty dry looking.

Confirmed during night time that the spark plugs are firing.

Tried spraying a bit of gas in each cylinder, putting the plugs back in, and cranking. Nothing. Which really baffles me. Dry plugs suggest no fuel, but putting fuel in the cylinders and getting nothing suggests bad ignition, right?

Clearly I'm getting something wrong here.

[Reefmagnet]

That does seem to be a mystery normally confined to the likes of chainsaws and weed wackers! Hard to think total loss of compression on a twin cylinder, but perhaps a blown crankcase seal or stuck reed valve is a problem. Could even be a blocked exhaust port. Although no two things ever fail at the same time, spark needs to be blue also as a yellow spark may not fire under compression.

And then there's the bleeding obvious things like bad fuel ( try Wd40 as a q&d fuel for squirting into the cylinders)? is the bowl actually full of fuel? will it run if pumping the fuel bulb (possible bad fuel pump); is the kill switch connected?

Also, best way to field clean a blocked jet is to ream it with a stiff enough strand of copper electrical wire.

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[Philsboat]

Originally Posted by MondayNever

Hi all,
I've got a 3-4 year old Yamaha 8c 2-stroke outboard. Up until today it had been starting in 1 or 2 pulls almost every single time. Today I drove it around on three occasions, then literally 5 minutes after I had stopped it after a quarter mile trip, she failed to start. Lots more cranking, no bueno.

I pulled the plugs and they looked rather sooty but totally dry, which suggests to me that she wasn't flooded. Pulled the starter a few times to be sure that the cylinders were clear then reinstalled a set of old plugs that worked when I swapped them out a few months ago. Also checked to make sure that both plugs were sparking, which they seemed to be as best as I could tell in full sunlight (finger jolt).

Pulled the little disposable inline filter and it looked clear. Also squeezed the bulb with filter removed from the engine side and it squirted fuel.

So.. fuel is at least arriving at the carb, spark plugs are sparking, pull start cranks it as fast as ever... what next? I don't know a thing about rebuilding/cleaning carbs, so hopefully you'll have another suggestion.

The only thing I can think of that was different about today was that I just filled up with a fresh tank of gas. I added oil, but only sloshed the tank around a little before taking off. I assume that I wouldn't be able to pull the starter if the pistons were siezed, though.

Any thoughts are welcome. Sailing out of Grenada tomorrow and would love to not have to row everywhere.

I had an eight hp Mariner(Yamaha) that was hard to start and stalled a lot.The fuel pump diaphragm was perforated with tiny holes so the gas would bypass the carb and go directly into the base causing it to run very rich(carbon on plugs).
T o prove it out squeeze the bulb when it is running.If it stalls replace the diaphragm.The bulb should get hard when the carb float bowl is full and the float valve shuts off the fuel.

[ChicF]

I have the exact same engine and had the exact same problem. Drove me nuts,tried rebuilding carbs changing plugs but finally changed the fuel inlet device. The one you plug the fuel line to the engine with and cured the problem. It seems ethanol in the fuel destroyed the old one and blocked the fuel.

[Brewgyver]

With the cover off the engine, can you see the carb throat? If so, squeeze bulb until it hardens up (carb bowl float closes needle valve), put choke full on and give rope 8-10 pulls. Looking at throat, open choke, you should be able to see liquid fuel. If not, your problem is almost certainly a clogged jet.
Look up your carb on the web, find an exploded parts diagram, it can be most helpful. Your looking for the idle speed jet. On older motors it was possible to get around the neutral start / throttle safety and try cranking with a half open throttle, which could sometimes get you started ecven with a blocked idle jet. I had to do that once with a 70s vintage Merc, when I HAD to use the dink to push my Catalina 30 most of the way back to port, but that may not be so easy to do with a motor as new as yours.
These are the times that try men's souls, or at least their arms! In the end, you'll learn from it and grow, assuming you don't yield to the all too tempting urge to reclassify it from propulsion to ground tackle!
Good luck!

[nockerwhite]

My grandson sorted my problem with a Yamaha 5 2str. There was a leakage of air into the carburetor feed - it had been dislodged by the gear linkage.

[ericoh88]

a friend of mine had an outboard which could not start. He traced it to the gasket between the carb and body . There was a hair line crack.

[44'cruisingcat]

Originally Posted by MondayNever

Pulled the carb last night and cleaned it as best as I could. Couldn't remove one of the jets due to not having a screwdriver that would fit, but soaked that area in acetone. Reassembled and still nothing. Lots of cranking but plugs stayed pretty dry looking.

Confirmed during night time that the spark plugs are firing.

Tried spraying a bit of gas in each cylinder, putting the plugs back in, and cranking. Nothing. Which really baffles me. Dry plugs suggest no fuel, but putting fuel in the cylinders and getting nothing suggests bad ignition, right?

Clearly I'm getting something wrong here.

Well that IS weird. Does it feel like there's reasonable compression?

If there's compression, and you put petrol down the plughole, and got no hint of firing, you'd have to suspect there's some kind of ignition problem.

It's reasonably fresh petrol right?

[44'cruisingcat]

Originally Posted by Brewgyver

These are the times that try men's souls, or at least their arms!

Some engines just seem like they'll never start:


https://www.facebook.com/MIX941Canto...15353/?theater

[tinkrman69]

As mentioned above...is the spark blue or yellow? if blue then the reed valves might be stuck open. when they are open you won't get the action to actuate the fuel pump...as it works on the pressure changes in the crankcase...and you won't get fresh air in the cylinder. hence no air on fire. Try spraying WD40 in through the carb throughout, whilst cranking. It might dislodge anything keeping the reed valve open. if the compression is there but not as strong as usual I would suspect valves or leak in the crankcase...ie...the split case seal. not easy to detect. try holding your hand over the carb throughout, to seal off any air, whilst cranking. and if it fires this way then suspect valve or case. remove carb and valve and clean and inspect. if good then crankcase would be next. with the sound of this thread a mechanic would be next.

putting fuel in through the spark plug hole is not always a good method, as it can short the plug. old fuel can cause not start. squirt fuel through the intake whilst cranking. it doesn't have to be mixed with oil, as it's only being used to get it started, not run for more than a minute.

if your spark is yellow? then try cleaning all there connections in the ignition system..ie..the connections at the ignition module, the con. at the coil's and the grounds for the coils...the little black wire and the mounting surfaces of the coils.

good luck hope it is as simple as cleaning the systems