8hp johnson 2 Stroke stops running when hot!

[John thomas]

I have just purchased a second hand 2003 2 Stroke Johnson 8hp outboard.
Perfect condition, clean almost new (looking)
When cold it starts and runs fine. When hot it will not idle and just cuts out. It is then impossible to restart it until it has cooled down to cold!
Today (we are in spain) we ran it for 5 minutes at full throttle, it was not running as fast as one would expect, and then it just cut out. It would not start again (blisters on finger from pulling) I then had to row the dinghy for an hour back to the marina. After it had cooled, it started and idles just fine.

What is the cause?????
1: the carb is CLEAN, the Fuel is NEW, the Filter is CLEAN, the main jet is CLEAN, the fuel Pipes are all CLEAN.
When it is hot and stops, the sparking plugs are DRY and CLEAN!!!!! which is an indication that they are not getting any fuel at all.
After it stopped I was under the impression that it was flooded and would not start because of this but this is obviously not the case.
For some reason, the engine, which runs superbly when cold, stops getting any fuel when it heats up.
Has anybody ANY idea what the cause could be????????

 

[VicS]

I have just purchased a second hand 2003 2 Stroke Johnson 8hp outboard. ............

If it suddenly drops dead suspect ignition. Check for two good sparks. They should be capable of jumping around 7/16" ( use a spark tester if possible, improvise if necessary)
If no sparks check stop/ kill switch otherwise suspect ignition power pack
Correct plugs are Champion QL86C gapped at 0.030" ( Dont use NGK resistor plugs. BZ7HS-10 if you have to use NGK plugs)
Check wiring and connections

If it dies more slowly suspect fuel problem.
Check tank vent. ( remove cap)
Try pumping priming bulb. If that keeps it going suspect fuel pump or air leakage into fuel line eg at connector.
50:1 fuel mix

When you say carb is clean. Do you mean you have stripped it and checked/ blown through all jets and passages or that it just looks clean?
Little clip that links needle valve to float arm in place ?
If the carb has a plastic top check for cracks.

My money would be on an ignition failure

Check it's not overheating. Good pee stream and a few drops or mist from relief port. It should be possible to touch and maintain figure contact briefly on any part of the power head except for the head around the plugs.

 

[John thomas]

Checked it all, done it all. I am giving it to a dealer today and let him try.
It was already with an "outboard expert" who could not find the fault.
I will definitely post the cause if we find it out.
Thank you anyway for your advice, but it was nothing new to what we have already checked through. It is not an ignition failure.

 

[Cloven]

If it dies more slowly suspect fuel problem.
Check tank vent. ( remove cap)

I had this problem with a brand new engine. Turns out the vent hole in the fuel tank cap had not been drilled right through. As said, loosen the cap and see if the problem still occurs.

 

[peteK]

Could be the coil breaking down when hot.Raise tank higher than engine to eliminate fuel pump.

 

[VicS]

My money would be on an ignition failure

To which end , I omitted to say, there is a good troubleshooting guide on the CDI electronics website

http://www.cdielectronics.com/support/

For any measurements you do need a peak reading voltmeter, or a DVA adapter for an ordinary meter

 

[Fantasie 19]

Sounds very much like the problem I had with my Tohatsu... I changed the plug and no more issues...

 

[John thomas]

the plugs are excellent, spark well BUT are dry when taken out when the engine has stopped, meaning no fuel!!!
Its not the fuel tank vent hole, it has a screw (separate tank) which is opened and a squeezy pump. all works perfect.
doesn`t seem to be the electronics as the spark is there but no fuel.

Why when the motor gets hot, does it not get fuel??? That is the problem (it seems) Tank is fine, hoses are fine, Impeller pump is fine, filter is clean, Carb. ist clean, jets, you can look and blow through. something between the carb and the cylinders, is happening, but what?

watch this space!!!!
I am very interested to see what the Spanish guy comes up with.

 

[VicS]

the plugs are excellent, spark well BUT are dry when taken out when the engine has stopped, meaning no fuel!!!
Its not the fuel tank vent hole, it has a screw (separate tank) which is opened and a squeezy pump. all works perfect.
doesn`t seem to be the electronics as the spark is there but no fuel.

Why when the motor gets hot, does it not get fuel??? That is the problem (it seems) Tank is fine, hoses are fine, Impeller pump is fine, filter is clean, Carb. ist clean, jets, you can look and blow through. something between the carb and the cylinders, is happening, but what?

watch this space!!!!
I am very interested to see what the Spanish guy comes up with.

Have you checked that the sparks will jump a gap of several mm. Its not good enough just to see them jump a small gap across the spark plug electrodes.

Have you tried continuously pumping the priming bulb to see if you keep it running by doing so

Check the fuel pump by disconnecting the hose between the pump and the carb. You should get a spurt of fuel when you crank the engine.

Check that the cam follower roller ( #3 in the diagram below) is in position and intact. Check also that the throttle valve will open fully

Did you check the clip ( #22) between the needle valve and the float arm. If its not in position the needle can stick on its seat ... then you get no fuel.

The only thing between the carb and the cylinders is the reed valve plate. #3 in the second diagram below ... but check there are no bad joints between the carb, the manifold and the crankcase.

 

[GrahamV]

It's interesting isn't it? This thread started back in 2017 and someone promised to let us know what transpired. But they didn't. Seems a human failing that we seek help when we are desperate but forget to give a bit back when the problem is resolved. Like many others, I have suffered the outboard blues from time to time. I'd like to be armed with some more solutions to the seemingly endless number of problems and their symptoms.

 

[RichardS]

I don't think it was mentioned but I would have just chucked some fuel (carb cleaner/2T mix) into the intake as soon as it cut out.

If it fires with the fuel chucked in it's a fuel problem ..... if it doesn't it's an ignition problem.

Richard

 

[sparkie]

It's interesting isn't it? This thread started back in 2017 and someone promised to let us know what transpired. But they didn't. Seems a human failing that we seek help when we are desperate but forget to give a bit back when the problem is resolved. Like many others, I have suffered the outboard blues from time to time. I'd like to be armed with some more solutions to the seemingly endless number of problems and their symptoms.

Yes a bit frustrating that. Happens regularly. I think that once the problem is solved it's just forgotten as you say. We should all try to add to the sum of human knowledge.... especially b....y outboard motors!

 

[jamie N]

I know that we'll never know now, but it would seem to me to be a cooling problem from salt build up in the cylinder block stopping water from circulating. Ask me how I know....

 

[sparkie]

I know that we'll never know now, but it would seem to me to be a cooling problem from salt build up in the cylinder block stopping water from circulating. Ask me how I know....

Go on then, how do you know.......??

 

[neilf39]

I reckon it is a cooling issue. I had the same when I had salt in the cooling channels. flushing did not fix it and had to take the head off to remove all the crud. Not had the problem since. I think the engine overheats and piston becomes tight and stalls the engine.

 

[Boathook]

I know that we'll never know now, but it would seem to me to be a cooling problem from salt build up in the cylinder block stopping water from circulating. Ask me how I know....

I've had the same problem with a Malta. Took quite a while to find out the problem ..................