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

When my Tohatsu started to cut occasionaly I took the carb apart (20hp) and there was an amount of white hard deposit in the carbuirettor. I thought of having it U/S cleaner but my local outboard shop although happy to try a clean for me advised me that these white cacium like deposits were unlikely to be removed only the gummy deposits of which there were none.
 
If you are going to recheck for blocked jets I found using a piece of soft copper wire worked well. This can be obtained by taking one or two strands from a light stranded copper cable. It can be quite difficult to tell if the jets are partially blocked so worth poking them out with the wire together with carb cleaner, and hold it up to a bright light.
 
Starts ... runs and then speeds up after few seconds - then stops ? That says to me Fuel Starvation ....

The shutting the throttle has nothing to do with it stopping.

It will not start if warm straight after - that means fuel is not there in chamber ... but starts if wait - that means fuel is getting there but slowly.

A common fault with carb diaphragm pumps - is the diaphragm itself. They dry out and appear to be OK - but they fail to flex enough with the changing crank pressure to feed fuel.

My penny bet is on the diaphragm .... every strimmer and 2str generator I've had - the diaphragm is the usual culprit if left significant period dry.
 
Paulg25 said:
View attachment 88874

Don't know if this helps at all.
Click to expand...
Often also a filter built into the top of the petrol tap inside the fuel tank.
And while we are the on the basics, check the air screw on the fuel cap.
Some of these allegedly, the rubber seal sticks despite the screw being undone.

But with no load, it really ought to run for more than a few seconds before enough fuel has be used to kill it.
 
C08 said:
I do not think most outboards have filters.
Click to expand...

I think a good many, if not most, do have a filter .....(I meant to include check filter in my post at #20)

Often in the tank outlet, sometimes as part of the fuel cock, Sometimes as an in-line filter, sometimes as part of the fuel pump assembly

The Malta's filter ( or strainer as it is called in the parts list) is in the tank outlet , #26 in the diagram below

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Paulg25 said:
View attachment 88874

Don't know if this helps at all.
Click to expand...
This is a Walbro type carb. As lw395 states the Malta has the filter in the fuel tap. I removed this in favour of an inline one some time ago.

To answer other questions, the choke is working fine and I replaced the pump diaphragm last year. I have just checked it and it hasn't gone hard.

I haven't been able to remove the main jet but have blown it through. I have cleaned the idle jets with fuse wire
 
VicS

I have tested the compression . It is about 5 1/2bar. i know this is low for a four stroke but what would you expect for a two str?

I have ordered a new plug but have to rely on mail order at the moment.
 
davidej said:
VicS

I have tested the compression . It is about 5 1/2bar. i know this is low for a four stroke but what would you expect for a two str?

I have ordered a new plug but have to rely on mail order at the moment.
Click to expand...
5½ bar ............ that's about 82 psi in old money They are never quoted AFAIK in the specs for small 2 st outboards but I think that's probably lowish .... but not so low that it won't run OK
 
Compression of a two stroke is a bit of a grey area, when cranking you only tend to see the piston compressing from the top of the ports.
It will depend a lot on how fast you can spin the motor.
And on a small engine, the plug thread volume adds a bit to the combustion chamber.
Unless it's really low, or you can do a good engine/bad engine comparison, it's not much help.
5 1/2 does not sound too bad in that light.
 
If this wee Yamaha has the crank seals gone...it would be the first I’ve ever heard of...within the realms of proper use. It’s a Yamaha after all.
there is a fuel pump...it’s a diaphragm pump.
You need to take the carb to bits...almost certain of it.
 
Still reckon its fuel starvation .....

Ignition would never cause it to speed up ....

If crankcase seals were duff - it would be hard to start - in fact you'd need to be spraying fuel into carb mouth to get it to start. (My Vire 6 would only run if I kept spraying fuel mist at the air intake ... crankcase seals were shot).
 
Refueler said:
It will not start if warm straight after - that means fuel is not there in chamber ... but starts if wait - that means fuel is getting there but slowly.
Click to expand...

With suspected fuel pump problems, an old trick is to spray fuel directly into the carb air intake, using any kind of domestic trigger pump container. If you can keep it running that way, it rules out most other potential problems.
 
If you suspect the fuel pump, you can feed the carb from a remote tank by gravity.
You can buy little plastic 'tanks' for the purpose, it's handy when you work on old motorbikes.
A 3HP engine should only be using of the order of a litre per hour, so a burette improvised from a 50ml syringe should run it for a while at low load.
You can raise the burette on a metre of tube to be sure there is enough pressure supplying the carb, I doubt much is needed.
Even a length of tube with fuel in it would show the carb drawing fuel to keep the float level correct, or not.
The other thing to be sure of regarding the pump would be is it leaking air into the crank case?
 
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