General 2-stroke advice

[steve.garlick]

Hi,

I have a 3hp Yamaha Malta. The symptom is that the engine dies after 1 - 2 hours of running. If I strip the carbie, blow out all the fuel, the engine runs fine again.

When the engine is in the 'fine' stage, it starts first pull, runs beautifully.

Can anyone think of what might cause this, or what I should look at. Fuel is good, spark is good. Flutter valve seems okay.

Any hypotheses welcome!!

Regards,

Steve

[donradcliffe]

Its a union motor and wants its coffee break. Seriously, how does it die, and what happens if you try to restart it? Does it kick over if you pull out the choke (then its definitely fuel)?

[steve.garlick]

It dies by the revs slowly dropping until it stops. Pulling the starter then has no effect, choke or no choke.

I'm imagining that the carby is getting flooded, rather than being starved of fuel. Is that a possibility? What would cause that?

STeve

[Sailmonkey]

Sounds like the float needle is a little sticky at times.

[perchance]

Check for spark after it dies to eliminate an ignition problem.

[sartorst]

I hate to ask but is the fuel tank vent open or clogged ? I have done it and rowed several miles

[colemj]

Good point on the vent - I have done this also.

Mark

[steve.garlick]

vent is open and unclogged. Spark is good,

Any other idea's. What do you do about a sticky float needle?

Steve

[Wraith_Mac]

Re. valve...
And we all laughed didn't we? Not here either, me also guilty of that, hangs head.

To the OP, if your tank isn't full you go 2-3 hrs before your wee little thing starves, loosen the cap completely then see if problem is solved.
Check for free airflow into carby as well and see if your engine is running too hot.
The solution to the first is obvious, the second leads to replacing or rebuilding to a greater or lesser extent.
I assume your fuel is well filtered and properly mixed with 2 stroke oil.
Cheers,
Mac

[tropicalescape]

check to see if the float is full of fuel when it cuts off ,may have a pin hole that takes a while to fill it up and then it will be to heavy to lift causing the fuel to shut off..maybe..good luck, of course if it has a pumper type(diaphram)this will not be the case ..

[onestepcsy37]

had the same problem with mine, rebuilt the carb a few times. finally decided to rebuild the fuel pump. problem solved. must have been a tiny leak of some kind which eventually let air into the fuel system, but not really sure.

[belizesailor]

Originally Posted by onestepcsy37

had the same problem with mine, rebuilt the carb a few times. finally decided to rebuild the fuel pump. problem solved. must have been a tiny leak of some kind which eventually let air into the fuel system, but not really sure.

One of my gueses too, check out the fuel pump. The typical 2 stroke fuel pump has thin rubber diaphrams which can develop issues.

Symptoms sound like fuel starvation. Given the time to develop, I would guess a vaccum leak somewhere...can be a bitch to isolate...I would start at the fuel tank and check each fitting between there and the carb. Have you changed any fuel system related fittings recently?

[ranger58sb]

We had a similar symptom once on an older motor. Turned out to be a pin hole air leak in the fuel line from the external tank.

-Chris

[Roy M]

Dirty little secret of outboard motor mechanics: MERCURY MARINE Power Tune at West Marine

Start the engine in water, pull off the cowling and shoot short bursts of Power Tune in carburetor. Engine sounds weird, belches large quantities of white smoke, then returns to running. Repeat this process until much of the can has been exhausted. Then increase the RPMs and shoot the remainder of the can into the carb. It will cough and sputter and die. Walk away for about fifteen minutes, or go have a cuppa, or whatever. Come back, start the motor, stay clear of the white smoke. Listen to the sewing machine you have just created. This stuff is my first step in renovating a sick outboard, followed by the more involved pulling of plugs, carbs, etc. Do this at the end of the season and it will probably be ready to start in the Spring.