Tohatsu 5hp 2 stroke runs fine for 20mins then quits and won't restart!

[liquidice]

I agree that this sounds like a fuel supply issue. The tank valve sounds like a good place to start, cracking open the fill cap should immediately defeat it. Also, in the interest of keeping it running “for now “, try to set up your tank as high as practicable above the motor so the fuel pump is doing minimal work and is assisted by gravity. Check all fuel lines and tighten or replace seals. I like to use screw collars. Squeeze the bulb till it floods (lil’ gas over the sides) full choke , throttle as high as it lets you, and try to pull start. Bowl will empty after a few tries, and then it should go. Also, try running with the cover off to see what you can see. I saw a Honda w/ s CDI and distributor that would vibrate the bolts loose, breaking contact and un-grounding a component, killing the motor. Once off, it would settle back into place allowing it to be restarted. I’ve seen a similar effect from a loose throttle handle. Best of luck!

[AlanR]

It could be the coil failing when it gets warm after running for a while.

When the engine stops, remove the spark plug, lay it on the engine with the HT lead connected, and turn the engine over. You should be able to see a nice blue spark. If not, suspect the coil, though it could be the points, if it has them.

When you take the plug out, after a few failed attempts to restart, it should be wet with fuel. If it is dry, you have a fuelling problem. Motorcycle theory states: If you think it is an ignition problem, it will be the carburettor, but if you think it is the carburettor, it will be ignition.

Good luck.

[Barney21]

Running for 20 mins would indicate CDI unit is faulty if it is not the fuel cap.
The CDI unit can be replaced with a Mercury unit as they are the same engine,unless this situation has recently changed . Black paint costs more than Grey??

[KP44]

This is very common and easy to fix.

This is a fuel issue. Likely the fuel tank cap vent is blocked. Try a new fuel tank cap or loosen the cap after 15 minutes and see if the engine keeps running.

Sometimes filling a fuel tank completely full gets fuel into the cap vent and stops the vent from working. Especially if you notice the squeeze-bulb in the fuel line is flat. That is from the engine drawing fuel until no more will come from the tank.

If this is not the issue, it is possible there is a mostly-blocked fuel filter that is part of the engine, or the fuel line from tank to engine is mostly-blocked. But I would first look at the fuel tank cap, or however your tank is vented.

[hzcruiser]

Looks like a lot of people would bet on the vacuum in the tank, so let us know if that was the case, please.


If not, I would check the electrical system going backwards from the plug to the coil.

I somehow suspect the engine doesn't care much whether spare parts are easy to come by wherever you are.

[sharpey]

Yeah, something weird going on with the external tank. I think there may be an air leak in there because the bulb doesn't stay hard.

Poured fuel into the internal tank & it runs like a top. So problem avoided for the time being.

Thanks folks. Much appreciate your input.

[ranger58sb]

Pinhole (air) leak in the fuel line from tank to motor. Try a replacement fuel line to check...

-Chris

[sharpey]

Originally Posted by ranger42c

Pinhole (air) leak in the fuel line from tank to motor. Try a replacement fuel line to check...

-Chris

Cheers, vwill do once we get back to Singapore.

[a64pilot]

I still think it’s the vent, if it were a leaking line etc, it wouldn’t run for 20 min.
If it’s the vent, it will run until out of fuel if the cap is loose.

It’s normal for the bulb to not stay hard, remember the line is under s tiny amount of vacuum. However if the bulb goes flat, that is another indicator of a stuck vent, or a disconnected line.

[liquidice]

Originally Posted by sharpey

Yeah, something weird going on with the external tank. I think there may be an air leak in there because the bulb doesn't stay hard.



Poured fuel into the internal tank & it runs like a top. So problem avoided for the time being.



Thanks folks. Much appreciate your input.

So happy that you found a solution that works for now! Thanks for the update and bon voyage!

[Cheechako]

It does sound like the fuel tank vent. But auto gas is terrible for small engines. My weed wacker wouldnt run properly. My emergency generator was used once and next time wouldnt run, I had to completely clean out the carbureator, the bowl was corroded inside. (should have completely drained it)
I have changed to non ethanol gas for all my small motors and ALL my problems went away. You can leave it in the engines indefinitely too. I used to think the ethanol issue was just a "urban myth"... not anymore.

[Cpt Pat]

Originally Posted by Cheechako

It does sound like the fuel tank vent. But auto gas is terrible for small engines. My weed wacker wouldnt run properly. My emergency generator was used once and next time wouldnt run, I had to completely clean out the carbureator, the bowl was corroded inside. (should have completely drained it)
I have changed to non ethanol gas for all my small motors and ALL my problems went away. You can leave it in the engines indefinitely too. I used to think the ethanol issue was just a "urban myth"... not anymore.

There is one common source of non-ethanol gas: 100LL (100 octane Low Lead) at airports. Many small airports have self-serve pumps. You will however have to deal with lead fouling of the spark plug, but that process is gradual. Spark plugs in cars last much longer ever since the lead was removed.

The reason ethanol-additive fuel is such a problem, especially in damp environments, is that alcohol is "water miscible" (see https://en.wikipedia.org/wiki/Miscibility). The ethanol absorbs water without saturating. Ethanol gas can suspend more water in solution that non-ethanol gas - and there is no practical way to "dry it out." Non-ethanol gas will also hold some water in suspension, but it is "immiscible" so the solution saturates at much lower water concentrations, and at saturation the water drops out to the bottom of the tank. Airplanes have fuel/water separators and sample valves at the lowest part of the tanks to allow the operator to see and remove water that has fallen out of solution during pre-flight inspection.

A countermeasure for limiting water build-up with ethanol gas is to limit the amount of air in the tank: keep it full, and keep it sealed when not in use. Adding fresh "dry" fuel will dilute the water contamination, so refilling the tank every time after a sail is a good idea. As water accumulates in the ethanol gas, the effective octane number drops, so I use "premium" with my Nissan (when I'm not seen sneaking away from the local airport with a gas can). Considering how little fuel I use, the price difference is irrelevant.

As for carburetor fouling: the Nissan manual recommends running the engine out of fuel at the end of the sail to avoid leaving fuel in the carb reservoir that will evaporate leaving a residue.

[Cheechako]

Non ethanol gas around here is available at some Union 76 stations and at farm supply places with pups. Farmers aren't required to use ethanol gas.