Unclogging a carburettor?

[C08]

I have a bad misfire on an outboard that comes and goes. I have changed the plugs but I have no reason to suspect an ignition problem. As the piping from the 2 tanks is old I have started by replacing all the fuel pipes, engine fuel filter and water seperator/filter cartidge working up to the carburettor. So my next job is to strip and clean the carburetor where I am expecting to find gum and sticky deposits ( the engine is 7 years old with about 600 hours on it). Are the carburettor cleaning sprays much better than just a petrol bath and a brush?

 

[anoccasionalyachtsman]

I have a bad misfire on an outboard that comes and goes. I have changed the plugs but I have no reason to suspect an ignition problem. As the piping from the 2 tanks is old I have started by replacing all the fuel pipes, engine fuel filter and water seperator/filter cartidge working up to the carburettor. So my next job is to strip and clean the carburetor where I am expecting to find gum and sticky deposits ( the engine is 7 years old with about 600 hours on it). Are the carburettor cleaning sprays much better than just a petrol bath and a brush?

I've just used petrol for years until I discovered 'brake and clutch cleaner' which is much the same as the other sprays. It works a little better than petrol, but not much. If you're not going to make a habit of it, stick with petrol.

 

[anoccasionalyachtsman]

ps. Misfires don't tend to be gummed carbs, but water in the float bowl can do it. Are the ignition leads clean and decent looking all the wail back to the coil/mag?

 

[LadyInBed]

If it has points, have you checked and burnished them?

 

[[3889]]

An outboard place near me will give a carb a sonic bath for a tenner.

 

[VicS]

I have a bad misfire on an outboard that comes and goes. I have changed the plugs but I have no reason to suspect an ignition problem. As the piping from the 2 tanks is old I have started by replacing all the fuel pipes, engine fuel filter and water seperator/filter cartidge working up to the carburettor. So my next job is to strip and clean the carburetor where I am expecting to find gum and sticky deposits ( the engine is 7 years old with about 600 hours on it). Are the carburettor cleaning sprays much better than just a petrol bath and a brush?

I would nevertheless for an intermittent misfire check for good sparks. Presumably at that age it has CDI ignition , not points, so would be looking at drawing sparks 7/16" from the ht leads. In line spark testers might be useful too.
Also check all connections on the ignition circuit wiring and the condition of the HT leads... coils as well if accessible.

Strip and clean the carb once you are absolutely sure there is no ignition fault, I'd buy a spray of carb cleaner as it will be useful to spray through orifices and passages . Rebuilding with a "carb kit would be sensible as to clean it properly you may have to remove plugs etc which cannot be reused

You dont say what engine ! There are many makes and even more different sizes

 

[lw395]

I find 'carb and throttle body cleaner' spray to be far superior to petrol.
I got mine from eurocarparts for about £2.
It removes the varnish which petrol deposits.
As well as dissolving any water-retaining slime.

 

[dom]

I use carb spray together with a car tyre foot-pump with a small plastic conical head. Air pressure is great for opening up intricate little passages like idle jets + helps avoid removing welch plugs, etc. The carb spray not only swiftly dissolves gunk, but being an aerosol is handy to spray into the jets & passages with the little tubular attachment they all come with. It also evaporates almost entirely so one has nice clean parts to reassemble.

For a couple of quid seems like a nobrainer to me.

 

[C08]

Thanks for ideas - the engine is a 20hp Tohatsu 4 stroke. The sparks run big and healthy although the old plugs looked on the whitish/greyish colour rather than a light chocolate brown so may indicate fuel shortage before dying? Using the primer bulb made no effect on erratic running. No sign of tracking when run in the dark and all leads look dry and clean. Whatever it turns out to be I need to do the carb for peace of mind and after 7 years of use it is overdue a bit of attention.
I had just entered Portsmouth when it started cutting out, a couple of minutes earlier would have been fun!

 

[dom]

I'd seriously think about a carb rebuild kit. They tend to include a few pointless bits an pieces, but also some vital o-rings, gaskets, jets, float seals, etc.

It will be a PITA if you service, test, and the damn thing floods, leaks, or whatever right in the middle of the warmest season we've had in ages :ambivalence:

 

[lenten]

if you can get a cheap professional sonic bath clean ---do it----i fiddled with my carb when engine was running a bit ragged----then gave up and had carb professionally cleaned---engine ran like new

 

[LadyInBed]

Does the fuel have an in line filter/strainer, if so, has it been cleaned/replaced/bypassed?

 

[C08]

Does the fuel have an in line filter/strainer, if so, has it been cleaned/replaced/bypassed?

Yes it has an inline Quicksilver Filter/Water Seperator with a new cartridge fitted and the small fuel filter under the cowel. No sign inside of the old filters of anything amiss. I normally let the engine run to dry but maybe not always so something perhaps festering in the float bowl?

 

[lw395]

Yes it has an inline Quicksilver Filter/Water Seperator with a new cartridge fitted and the small fuel filter under the cowel. No sign inside of the old filters of anything amiss. I normally let the engine run to dry but maybe not always so something perhaps festering in the float bowl?

I expect so.
First thing to try, remove float bowl, squirt bowl and carb with cleaner, blow dry and replace.
This often works and avoids the risk of making things worse, unless you happen to trash the float bowl gasket.
Somes just removing the drain screw and running some fuel through will remove gunk and water.

 

[C08]

Thanks for suggestion LW but I do not think on this engine the float bowl is very accessible, the Seloc WM I have suggests that taking the whole unit off is easiest i.e. the manifold and carburrettor complete. Quite a lot of gubbins to remove before that eg air intake and the remotes and linkages so not a tiny job.

 

[MedinaView]

Used to run redex through the lawnmower when the carbs were dirty.

 

[lw395]

If the float bowl is hard to remove, then it might be worth trying a good squirt of carb cleaner into the carb's fuel inlet.
If you don't use the engine often, it might be worth using a top-grade fuel like the expensive BP one.
Possibly also a stabiliser additive, some small engine users say great things about these, but I don't use one personally.

 

[C08]

If the float bowl is hard to remove, then it might be worth trying a good squirt of carb cleaner into the carb's fuel inlet.
If you don't use the engine often, it might be worth using a top-grade fuel like the expensive BP one.
Possibly also a stabiliser additive, some small engine users say great things about these, but I don't use one personally.

A good suggestion however I am committed to cleaning out the carb just to be sure as wife was having kittens when entering Portsmouth with a misfiring engine and no wind.

 

[Stemar]

I had a similar problem with a 3.5 HP 2T Tohatsu - all the symptoms of fuel starvation. I cleaned the carb thee times to no avail. The issue turned out to be corrosion where the coil earth is attached to the engine block. A good clean and a dose of ACF50, and it's been fine ever since.

 

[C08]

I had a similar problem with a 3.5 HP 2T Tohatsu - all the symptoms of fuel starvation. I cleaned the carb thee times to no avail. The issue turned out to be corrosion where the coil earth is attached to the engine block. A good clean and a dose of ACF50, and it's been fine ever since.

Thanks I will check the earth.