I'm beginning to despair of ever getting my Malta O/B to run properly

[davidej]

It's a Yamaha Malta 2 Str with a neutral gear so I have been trying to run it in a barrel of water.

It starts easily enough, then seems to rev right up and as I throttle back from starting position it dies. I don't seem to be able to keep it running for more than 15-20 seconds

It has been giving trouble for some time. Last year it went to professionals and had had hte carb ultrasound cleaned. This year, I have mixed fresh fuel, made sure it flowed through the on/off tap, stripped down the carb again and blown all the jets and passages through with carb cleaner.

I also had the head off and cleared the water passages to make sure it was not over heating

I have to date assumed it is a fuel problem, but I am beginning to wonder if I am looking in the right place.

Could it be some kind of breakdown in the ignition system. I notice trying to restart immediately after a run is difficult, but it is easy if I leave it for 10 minutes.

Any suggestions?

 

[anoccasionalyachtsman]

When you say 'rev right up' does that mean to more or less full throttle? If so, will it stay running at high revs? The way I'm reading it though is that you get it to start at the part throttle position and are immediately dropping it back to idle, at which point it stops. If the latter, try keeping running at the higher revs for a while and see what happens then.

The hot start thing may be a clue, but nor enough info yet.

 

[V1701]

The rubber fuel hose may be the culprit...

 

[lw395]

When it dies, whip the plug out and see if it's wet or oily.
cranking it over with the plug out a few times to get rid of excess fuel and oil is worth doing.
A new plug is always a good idea.

 

[davidej]

To answer some of these questions

1. I have been starting it in neutral with the throttle in start position ie about one third. As soon as it picks up, the revs rise until it is screaming. Trying to throttle back makes it die.
I have just tried starting it in gear. Obviously the revs do not rise as much but it still dies after about 15 secs.

2. I have replace the rubber fuel piping with Tygon. I don't think it can be fuel starvation as , after running, I have loosened the float chamber drain screw and the chamber seems to be full.

3. I have checked the plug after running and it is definitely not wet or oily - a new one was fitted last year when the professionals had it (for all the good they did!!!).

I have heard stories of ignition systems breaking down with heat, at then being OK once they have cooled down. Could this be my problem? How could I check?

 

[Boathook]

To me it is the slow running jet. I wouldn't have thought the engine hot enough for the electrical system to breakdown.
The slow running jet screw needs to be about 1.5 to 2 turns out as a rough set up. This also caused me no end of problems with mine. The smallest amount of debry in the jet causes problems and you struggle to see this by eye alone. If you hold the jet up to your eye (assuming perfect eyesight) if you think that the hole looks or seems not perfectly round it has a 'blockage'.
I find that to start it only requires a small amount of throttle and the marks on the handle are only a guide. If you decide to bin the engine I will take it of your hands once non essential travel is allowed!

 

[RichardS]

It's definitely not overheating so it is either fuel or ignition.

What I would do is start it as usual then, ideally with any air filter removed if that is possible. Then, as soon as it stops, squirt/drip a ml/few drips of pre-mix into the air intake and then immediately try to start it again. If it fires for a few strokes, then the fuel/carb is your problem. If the engine does not fire at all, there is no spark and the problem is probably the HT side

You can try it a few times, cleaning the plug after each attempt, until you are sure that you have nailed it. I think you will find that it fires after the "direct injection".

Richard

 

[lw395]

The dry plug suggests fuel rather than ignition.
The racing and cutting out might lead me to check float valve operation.

Take the drain screw out of the carb, put a container( I use a foil takeaway container) under it to catch the fuel and check the fuel flow rate is reasonable when you turn the petrol on.

I once bought a motorbike for very little money as a non-runner. It turned out that the air filter was assembled wrongly.

I'd also check for carb gasket leaks.

 

[anoccasionalyachtsman]

I still get the impression that it would continue to run if you don't cut the revs yourself?

Coils can get flakey when hot, but I don't think you're running it long enough for that to happen.

I think dirty idle jet too. Maltas (or at least the four I've used) are brilliant engines except that they seem to be more picky about dirt in the idle jet than any other engine I've known.

 

[Paulg25]

Are you sure it's not the fuel filter. I have a strimmer that does the same. Been to main dealer who said carb' was buggered.

Eventually tracked it down to a gauze filter built into the carb.

 

[QBhoy]

This is almost certainly a carb and jet issue. If it was just U/S cleaned and not properly done, then I’d say it’s then a certainty it’s carb and or jet related. Have a good look at the fuel pump Diaphragm in the light for signs of holes or wear too.
Just finally...I’m sure you’ve checked this and it’s way too obvious, but just thought I’d mention silly things like the primer bulb being the right way round for flow...the vent being open on the top of the inbuilt tank...and perhaps less obviously, the fuel on/off valve being clear of dirt or obstruction. I’ve been victim to the latter a few time’s. Easily sorted by removing and blowing through it. Or proving fuel flow by removing the fuel pipe on the carb side of the valve and opening.

 

[escapism]

An ignition problem is very unlikely to cause the symptoms you describe. There can certainly be thermally induced issues with ignition systems that are very hard to trace, but they result in misfiring/cut out as the components warm up/overheat. I would focus on the fuel system. Lots of good suggestions already made above.

 

[QBhoy]

If you are struggling with having a go at the carb yourself...let me know. I have one in bits just now.

 

[rotrax]

In my extensive experience of small two stroke engines and Japanese carbs I think it unlikely for it to be an idler jet. The revving once started on start position would indicate a crankcase seal leak, confirmed by harder starting once it stops.

Might be wrong, but exactly the same symptoms with small motorcycle engines nearly always proved to be crankcase seals/worn main bearings.

If there is a reliable fuel feed, a clean carb and good sparks, why is it stopping when its revving its nuts off, and why is it revving its nuts off at 1/3rd throttle? IIRC the ignition timing is not quite at full advance then either, so in normal use, restricting the RPM.

Air leak from leaky crank seals sound more likely to me.

 

[davidej]

I have take the advice offered her

1. Idle screw set a two turns
2. Fuel flow checked. a good flow out of tap. The float chamber drained then a little spurt each time I pulled the starter cord with plug lead off. This indicates to me that the pump is OK
3. No need to prime- would restart after each run.

But starts easily - runs ok for 10 secs or so then revs rise and ,as I try to control them by throttling back, it dies.

I am going to take up the offer of help with one last carb clean and if that does not work, I will investigate the crankcase seal.

Thanks for you help so far.

 

[Boathook]

If the crankcase seal is the bit I'm thinking off, the engine will have to be stripped down. I would just try the carb first plus new gaskets on the associated parts. A smear of grease on the gaskets will help future removal and block any small gaps ......
There was an earlier thread about the malta that I started and it was being commented upon recently. If I can find it I will edit this post and add the link. All difficult on a tablet I find.
Hopefully the link below will work
Yamaha Malta

 

[lw395]

I have take the advice offered her

1. Idle screw set a two turns
2. Fuel flow checked. a good flow out of tap. The float chamber drained then a little spurt each time I pulled the starter cord with plug lead off. This indicates to me that the pump is OK
3. No need to prime- would restart after each run.

But starts easily - runs ok for 10 secs or so then revs rise and ,as I try to control them by throttling back, it dies.

I am going to take up the offer of help with one last carb clean and if that does not work, I will investigate the crankcase seal.

Thanks for you help so far.

My bold.
I don't think there is a pump?
Is the carb not gravity fed from the tank at the top of the motor?
Must admit it's some years since I had a Malta to bits, I have a Yam 2.
There is a pump operated by crank case vacuum on the 4 I had, but fuel would just flow through that by gravity when using the internal tank.

I don't disagree with Rotrax's knowledge of crank seals, but I don't think you've eliminated the carb and so forth yet.
Crank seals are a big job, you'll need a tool to get the flywheel off.
An air leak between carb and crank case can much do the same.
I assume you're not using the choke at all, or knocking it off as soon as the motor fires?
Check that the choke blade is actually opening, some outboards have choke linkages which can be got wrong.

Make sure you are not starting from a point of having a lot of fuel in the crank case.

You can get vaguely similar effects from a partly blocked exhaust.
It's a reed valve motor unless I'm confused, but I think if it starts, the reeds are probably OK?

I would still be looking at the float valve. Does it flow enough? Does it shut off at the right level?
Is the float bowl gasket sound?

 

[davidej]

There is a crankcase pressure actuated diaphragm pump on the side of the carb. I got a spare one some time ago so I have a dismantled one to look at. I doubt that gravity would take fuel past the little reed valves inside - the head is only 3-4 inches.

I have checked the float and valve and they seem OK.

This problem has persisted over several years and it has been to two different companies. Both of them ultrasound cleaned the carb. The first one seemed to fix it for a season (but not much use) and the second not at all. While I haven't entirely discounted a carb problem, I am just wondering if it isn't something more deep seated.

I have another OB but I would like to get this sorted so I can leave the little Honda on the pushpit for use with the rubber dubby and use the Malta for the GRP tender to the mooring.

 

[VicS]

I have take the advice offered her

1. Idle screw set a two turns
2. Fuel flow checked. a good flow out of tap. The float chamber drained then a little spurt each time I pulled the starter cord with plug lead off. This indicates to me that the pump is OK
3. No need to prime- would restart after each run.

But starts easily - runs ok for 10 secs or so then revs rise and ,as I try to control them by throttling back, it dies.

I am going to take up the offer of help with one last carb clean and if that does not work, I will investigate the crankcase seal.

Thanks for you help so far.

My bold.
I don't think there is a pump?
Is the carb not gravity fed from the tank at the top of the motor?
Must admit it's some years since I had a Malta to bits, I have a Yam 2.
There is a pump operated by crank case vacuum on the 4 I had, but fuel would just flow through that by gravity when using the internal tank.

I don't disagree with Rotrax's knowledge of crank seals, but I don't think you've eliminated the carb and so forth yet.
Crank seals are a big job, you'll need a tool to get the flywheel off.
An air leak between carb and crank case can much do the same.
I assume you're not using the choke at all, or knocking it off as soon as the motor fires?
Check that the choke blade is actually opening, some outboards have choke linkages which can be got wrong.

Make sure you are not starting from a point of having a lot of fuel in the crank case.

You can get vaguely similar effects from a partly blocked exhaust.
It's a reed valve motor unless I'm confused, but I think if it starts, the reeds are probably OK?

I would still be looking at the float valve. Does it flow enough? Does it shut off at the right level?
Is the float bowl gasket sound?

The correct initial setting for the idle mixture is 1 to 1½ turns out from gently seated ..., not as stated earlier in the thread

There is a fuel pump.... RTFM

Clean the idle jet with a soft copper wire

Check the float height is correct ( see the manual). Check the clip between needle and float arm is in position while you are in there. Check that the float valve does properly seat and shuts the fuel flow off .

Try a new plug ( I know the previous "professionals" allegedly fitted a new one but the failed to sort the motor out. ( Correct plug is NGK B6HS-10 , gapped at 0.9 - 1.0 mm)

Check the strength of the spark ( preferably using an adjustable gap spark tester .... but easy to improvise) You should get a good hot blue spark which will easily jump well over 1/4". ( just checking for a spark across the plug electrodes is not good enough.

If you have a compression gauge, or can borrow or steal one, check the compression

Check for air leaks around fuel pump and carb ........... Crank case seals are a big job .... leave 'til all easier options are explored and eliminated.

Check correct operation of the choke and also throttle

A workshop manual which covers the engine can be found at Boatinfo - The library, containing manuals, brochures and other technical documents from the last hundred years!

 

[C08]

Are you sure it's not the fuel filter. I have a strimmer that does the same. Been to main dealer who said carb' was buggered.

Eventually tracked it down to a gauze filter built into the carb.

I do not think most outboards have filters.