2-stroke won't run without choke

Mike2309

Mike2309

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Very simple Mariner5 air-cooled 2-stroke runs fine on half-choke , dies on anything less. I've had the carb off and cleaned it (though, oddly, I couldn't remove the main jet which is held up in place by a plug in the top of the float chamber . With plug removed the jet seems to levitate in the threaded hole , it rotates but neither rises nor falls)
Gaskets seem fine .
The idle jet screw does nothing, by the way. If the needle were worn you would think it would assist, if anything, in keeping the engine running.
Something subtly wrong with the level of fuel in the float chamber? Float is not damaged (and it would have to float higher to starve the jet wouldn't it?)
Sucking air through worn throttle spindle? Doesn't seem slack.Next session perhaps a drop of oil on the spindle while it's running might effect a very temporary cure , or at least be seen to be sucked in , and prove the point.
Should I just adjust the choke control so that half-off is as far as it goes?
What more can I do?

Actually now that I see it in print I wonder if I have really cleaned the main jet if I've not removed it. It's had a soak with carb cleaner and a blow through that's all, though with a lamp shining through the carb I could see a pinpoint of light looking up-the-way through the jet.
 
Mike2309 said:
Very simple Mariner5 air-cooled 2-stroke runs fine on half-choke , dies on anything less. I've had the carb off and cleaned it (though, oddly, I couldn't remove the main jet which is held up in place by a plug in the top of the float chamber . With plug removed the jet seems to levitate in the threaded hole , it rotates but neither rises nor falls)
Gaskets seem fine .
The idle jet screw does nothing, by the way. If the needle were worn you would think it would assist, if anything, in keeping the engine running.
Something subtly wrong with the level of fuel in the float chamber? Float is not damaged (and it would have to float higher to starve the jet wouldn't it?)
Sucking air through worn throttle spindle? Doesn't seem slack.Next session perhaps a drop of oil on the spindle while it's running might effect a very temporary cure , or at least be seen to be sucked in , and prove the point.
Should I just adjust the choke control so that half-off is as far as it goes?
What more can I do?

Actually now that I see it in print I wonder if I have really cleaned the main jet if I've not removed it. It's had a soak with carb cleaner and a blow through that's all, though with a lamp shining through the carb I could see a pinpoint of light looking up-the-way through the jet.
Click to expand...



Do you push the carb up as far as it will go in the sleeve before clamping it up. If you dont then air will leak in at the clamp. It is possible there should be an O ring. I had the same problem with a similar Yanma.
 
"Do you push the carb up as far as it will go in the sleeve before clamping it up. "

Do you mean the jet there ? If so I'll check that. Thanks.
 
Mike2309 said:
Very simple Mariner5 air-cooled 2-stroke runs fine on half-choke , dies on anything less. I've had the carb off and cleaned it (though, oddly, I couldn't remove the main jet which is held up in place by a plug in the top of the float chamber . With plug removed the jet seems to levitate in the threaded hole , it rotates but neither rises nor falls)
Gaskets seem fine .
The idle jet screw does nothing, by the way. If the needle were worn you would think it would assist, if anything, in keeping the engine running.
Something subtly wrong with the level of fuel in the float chamber? Float is not damaged (and it would have to float higher to starve the jet wouldn't it?)
Sucking air through worn throttle spindle? Doesn't seem slack.Next session perhaps a drop of oil on the spindle while it's running might effect a very temporary cure , or at least be seen to be sucked in , and prove the point.
Should I just adjust the choke control so that half-off is as far as it goes?
What more can I do?

Actually now that I see it in print I wonder if I have really cleaned the main jet if I've not removed it. It's had a soak with carb cleaner and a blow through that's all, though with a lamp shining through the carb I could see a pinpoint of light looking up-the-way through the jet.
Click to expand...
What is the serial number of the engine. ?

Running only when choked is usually a sign of a dirty carb

Does the carb look like THIS
If it does I would say remove and clean the main nozzle #6 by pushing a soft copper wire through it. It is not good enough to be able to see a pin point of light through it . Watch out for the gaskets #5 and #7.

Clean also all the jets # 8, 10,11 and 12.

The float should be adjusted so that the needle valve just closes when the float is horizontal / parallel with the float chamber to carb body joint
 
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Make sure the main jet is clean, not just light shining through!
If the main jet is gummed up then there is a fair chance the float needle will be gummed up too leading to a poor fuel supply.
Throttle valve spindles need to be seriously worn to affect normal running so I would probably discount that.
Have you checked that the air bleed screw in the tank filler cap is opening properly and have you cleaned the fuel filter at the fuel tap? The actual plastic fuel lines gum up as well and need cleaned out too on a regular basis. Check too the pipe where the fuel goes into the carb, i.e. between the fuel supply pipe and the float valve.
If your carb is fitted with a fuel pump diaphram you may find it may be leaking and need replacing.

In effect, clean EVERYTHING between the filler cap and the crankcase!!

These engines can be a bit temperamental, mine will not even start without the choke even when hot. Best of luck.
 
VicS said:
What is the serial number of the engine. ?

Running only when choked is usually a sign of a dirty carb

Does the carb look like THIS
If it does I would say remove and clean the main nozzle #6 by pushing a soft copper wire through it. It is not good enough to be able to see a pin point of light through it . Watch out for the gaskets #5 and #7.

Clean also all the jets # 8, 10,11 and 12.

The float should be adjusted so that the needle valve just closes when the float is horizontal / parallel with the float chamber to carb body joint
Click to expand...

Thanks for that. It's pretty much like that but there are no jets 10 and11 under the plate, and the float does not have integral pivot it bears (up)on a sort of pivotting wishbone . Adjusting the level would mean bending that wishbone I presume.
 
SAMYL said:
Make sure the main jet is clean, not just light shining through!
If the main jet is gummed up then there is a fair chance the float needle will be gummed up too leading to a poor fuel supply.
Throttle valve spindles need to be seriously worn to affect normal running so I would probably discount that.
Have you checked that the air bleed screw in the tank filler cap is opening properly and have you cleaned the fuel filter at the fuel tap? The actual plastic fuel lines gum up as well and need cleaned out too on a regular basis. Check too the pipe where the fuel goes into the carb, i.e. between the fuel supply pipe and the float valve.
If your carb is fitted with a fuel pump diaphram you may find it may be leaking and need replacing.

In effect, clean EVERYTHING between the filler cap and the crankcase!!

These engines can be a bit temperamental, mine will not even start without the choke even when hot. Best of luck.
Click to expand...

I've replaced fuel lines and filter, and it has an external tank, so I've covered some of the above. I'll try the rest of it on some evening that England have not just beaten the Ukraine 1-0 to progress beyond the group stage of .........
 
Sounds like an old rebadged Yamaha one.

Yes the float adjustment will be made by bending the yoke but it should not the overly critical. I dont know what the correct height is
 
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thanks again Vic.
Didn't give you the serial number before, it's 661 312426.The diag of the carb (although it's not exactly the same as mine) does explain why I couldn't get the main jet out. Mind you, how do you get it out against the grip of those two O rings? is it okay to push it down from above ?
I've been in touch with Outboards Direct for availability of gaskets etc (recommended in this forum I think) but they have a health/medical situation at the moment and are unable to reply.
 
The diagram is the one for that number ...1979 model.

Id think you will have to be very careful about pushing that nozzle out. Easily damaged Id think. I dont know if its possible to clean it properly in situ or not.

If you cannot get any help from Oakley I guess you will have to take pot luck with the Dealer list on the Mariner website
 
For carb cleaning, I usually strip it as much as possible, then bring to the boil in a pan of water and simmer for 10 minutes.

Serve with in-season vegetables. ;)
 
At that age it may have a weak spark due to degredation of the ignition system.

I have a '82 Evinrude 4hp twin with two cylinders. It also needed choke to run.

Turned out that one coil was damaged and the spark only seemed to work when running rich. Don’t understand that myself, but the only thing I did to fix it was overhaul the ignition, and all was well again.

I diagnosed the coil by accident – was spraying the carb in ether (to look for air leaks) when the dodgy coil ignited the ether and the carb. To extinguish the fire I stopped the engine and dropped in top-down into the test tank.....
 
Mike2309 said:
"Do you push the carb up as far as it will go in the sleeve before clamping it up. "

Do you mean the jet there ? If so I'll check that. Thanks.
Click to expand...

Yes exactly if the same as mine. The sleeve it slides in may have a thin slot in the bottom to allow clamping action. The carb must be pusshed in so this slit is blocked off. IE snug against the engine. This cured mine. I think there are a few engine makes based on te same model and yours may be one.
 
Emulsion tube?

Tommyrot said:
For carb cleaning, I usually strip it as much as possible, then bring to the boil in a pan of water and simmer for 10 minutes.

Serve with in-season vegetables. ;)
Click to expand...

+1

Also use proprietary carburettor cleaner spray, from most motor factors, on the stripped carb, being careful to blow it through all the passageways and jets. Beware, it's flammable & nasty stuff but great for removing wet sikaflex from things...

The 'main jet which levitates' sounds like the emulsion tube, which can be pushed down with a lollipop stick from inside the venturi. It will have a number of holes on the side which easily block and could well be your problem.
 
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