2 stroke dies occasionally in gear

[Xgzfutfgut]

I have a 50 hp tohatsu 2 stroke 2003 automixing model
When I take it out it will run well for hours but at some point it suddenly stalls. When I start it again it will start fine but it will probably stall again shortly. sometimes the problem goes away. Sometimes when I start it again it will be stuck with low revs like limp mode. Trying more throttle will stall it. This also usually goes away.
Recently I have gotten replaced:
Spark plugs, onboard fuel filter, cleaned carbs, new impeller.
I can’t see any leaks in fuel lines and I have gotten mechanics to take a look at the issue but no luck.

The issue takes hours to happen so It’s hard to test otherwise it runs fine.

I would appreciate any feedback

[Fenlander]

Hi and welcome to the forum.

Do you mean this only happens when the engine is hot having been run for some time?

[Xgzfutfgut]

Originally Posted by Fenlander

Hi and welcome to the forum.

Do you mean this only happens when the engine is hot having been run for some time?

Pretty much heat. But I have had the boat stuck in low revs like limp mode when it was cold multiple times. But as for the stalling problem it has not done it cold. As far as I know there is a heat alarm and overheating shouldn’t kill the engine either but next time I go out I will try feel the water coming out of the impeller. I just can’t seem to find anyone with the same problem.

[beamishken]

When you say it stalls do you mean it stops as your going along at speed or when manoeuvring at idle speed?

[Xgzfutfgut]

Yes in gear and it has happened mostly at a higher speed. It is sudden almost like a kill switch. The engine doesn’t sound any different before it dies.

[beamishken]

I had a similar issue & it was a faulty fuel connector allowing air into the fuel line took ages to find it, maybe worth checkin or even try plumbing direct to the tank to remove the plug in connectors from the system to eliminate them

[Fenlander]

Like Ken I'd have a forensic look at every part of the fuel feed. But I asked about the time run/heat as sone of my most baffling vehicle issues have been with heat soak intermittent failure of ignition components.

[GAVMAC321]

Have the carb float heights been checked ?

[Xgzfutfgut]

Ah ok. I was told by the mechanic that they were faulty but that once the vacuum started they shouldn’t be an issue. I’ll try eliminating that then.

[Xgzfutfgut]

Originally Posted by GAVMAC321

Have the carb float heights been checked ?

No. I only cleaned the carbs. There was nothing glaringly wrong about the floats but I wasn’t looking. Do you think the issue i described sounds like carb floats? I think I have seen that it could have something to do with the loss of power

[spartacus]

2-strokes, air, fuel, spark. The last part is a built disingenuous, with HT leads, butterfly valve on air box, etc.

Earlier comment about checking fuel. I had a pattern part Tohatsu fuel connector (engine side) and the ‘o’ ring had dislodged, allowing air to get in. Ensure the connectors are genuine Tohatsu and there’s no air entering. It’s a small thing, but these pattern parts are junk. On the fuel primer bulb, ensure that’s not restricting fuel. Quicksilver are as good as Tohatsu.

When the carbs were cleaned, what were the fuel bowls like. Any discolouration, gunk. How were the carbs cleaned, ultrasonically?

[Xgzfutfgut]

Originally Posted by spartacus

2-strokes, air, fuel, spark. The last part is a built disingenuous, with HT leads, butterfly valve on air box, etc.

Earlier comment about checking fuel. I had a pattern part Tohatsu fuel connector (engine side) and the ‘o’ ring had dislodged, allowing air to get in. Ensure the connectors are genuine Tohatsu and there’s no air entering. It’s a small thing, but these pattern parts are junk. On the fuel primer bulb, ensure that’s not restricting fuel. Quicksilver are as good as Tohatsu.

When the carbs were cleaned, what were the fuel bowls like. Any discolouration, gunk. How were the carbs cleaned, ultrasonically?

The carb bowls were very clean. I just sprayed them with carby cleaner and took the valves out to clean as well but I don’t think I ever saw any gunk.

[Peter_C]

Not uncommon for a black box (CDI unit) failure causing loss of spark or limited RPM's. Unfortunately there really isn't much of the way in testing without a lab scope. I went through two black boxes with my old Evinrude 2 stroke 40HP. It would stall and restart but only at a limited RPM. It was too random to test though, so I went with replacement in hopes it would fix it and it did.

[Xgzfutfgut]

I tested it again today and I realised that It actually stalls when I use full throttle. It was constantly stalling at about 5000 revs. I have done a bit of research but haven’t found a reason. Does anyone know what this might be?
(It also stalled once in gear and lower Revs as it was cold but that could be a different issue)
I have also replaced the fuel connector which was faulty, that wasn’t it.

[willk]

Are you happy that the 2 stroke automix is working correctly? Hard to know, but you should have some idea of normal consumption. Have you tried running on pre-mix?

On another tack, is sufficient fuel actually being delivered at high revs? Is the bulb on the fuel line hard after the engine stalls?

[Pikey Dave]

Originally Posted by Xgzfutfgut

I tested it again today and I realised that It actually stalls when I use full throttle. It was constantly stalling at about 5000 revs. I have done a bit of research but haven’t found a reason. Does anyone know what this might be?
(It also stalled once in gear and lower Revs as it was cold but that could be a different issue)
I have also replaced the fuel connector which was faulty, that wasn’t it.

Is it happy all the way up the rev range to the point where it stalls? Will it accelerate & behave normally below the stall point, or is it reluctant & sluggish?

[Xgzfutfgut]

Originally Posted by Pikey Dave

Is it happy all the way up the rev range to the point where it stalls? Will it accelerate & behave normally below the stall point, or is it reluctant & sluggish?

It is usually fine until you hear it rev louder for just a second then it stalls

[Xgzfutfgut]

Originally Posted by willk

Are you happy that the 2 stroke automix is working correctly? Hard to know, but you should have some idea of normal consumption. Have you tried running on pre-mix?

On another tack, is sufficient fuel actually being delivered at high revs? Is the bulb on the fuel line hard after the engine stalls?

The bulb isn’t hard after stalling but usually when I run it for a bit (and it’s running fine) the bulb will be soft also. What I need to try next is have someone pump it as I stall it

[Xgzfutfgut]

Originally Posted by Peter_C

Not uncommon for a black box (CDI unit) failure causing loss of spark or limited RPM's. Unfortunately there really isn't much of the way in testing without a lab scope. I went through two black boxes with my old Evinrude 2 stroke 40HP. It would stall and restart but only at a limited RPM. It was too random to test though, so I went with replacement in hopes it would fix it and it did.

Yea I have similar issues to cdi failure but hopefully that isn’t it. It’s the most expensive part

[beamishken]

Originally Posted by Xgzfutfgut

It is usually fine until you hear it rev louder for just a second then it stalls

Most engines when they run out of fuel pick up the rpm before they die out. This suggests fuel is your issue . I'd be looking for possible points of air ingress or fuel restrictions in the fuel feed system