Unblocking Outboard Carb Jets?

[Tim Good]

My Mercury 3.5hp decided no to idle. When I start it i have go right away and at 1/3 power or more. Any less and she doesn't like it. Certainly won't idle.

I read elsewhere it might be a blocked jet as I've already dismantled the float chamber and cleaned several times. There are references to putting fishing wire through it in order to clean and then others say no never put anything through it.

Can anyone clarify before I embark on this?

 

[Carmel2]

Ultrasonic bath might help.

 

[Tim Good]

Ultrasonic bath might help.

Currently half way up the coast of Norway. Needs to be a DIY job.

 

[Muddy Boat]

Sometimes you can clear it by blowing. But if a prod is required, fishing line would be better as it is softer than metal wire, but otherwise thin wire or a strand from a wire brush are often used. Not ideal for the purists, but will do the job!

I believe there are 2 jets on these (if a 4 stroke). One (I think the idle jet) can be removed from the side/top of the carb and the main jet is located underneath inside the float bowl.

If removing, it is worth blowing / carb cleaner in all the holes to remove any debris in the internal passages.

Good luck

 

[TangaraToo]

I have a small brass wire brush that donates one of its bristles for doing this job. Softer than steel so less chance of scratching. I also remove jet and leave to soak in carb cleaner for 30 minutes first.

 

[steve66]

I have a small brass wire brush that donates one of its bristles for doing this job. Softer than steel so less chance of scratching. I also remove jet and leave to soak in carb cleaner for 30 minutes first.

You wont have anything small enough to poke through a 3.5hp idle jet onboard. Cant post a link atm but look on boats.net and you will see an exploded diagram of the carb. Blowing or sucking may do it otherwise its ultrasonic clean

 

[VicS]

My Mercury 3.5hp decided no to idle. When I start it i have go right away and at 1/3 power or more. Any less and she doesn't like it. Certainly won't idle.

I read elsewhere it might be a blocked jet as I've already dismantled the float chamber and cleaned several times. There are references to putting fishing wire through it in order to clean and then others say no never put anything through it.

Can anyone clarify before I embark on this?

A fine wire is sometimes the only way unless you have an ultrasonic cleaning bath up your sleeve or a powerful airline.
Preferable though to use brass or copper ( eg fuse wire), rather than a steel wire such as a bristle from an ordinary wire brush.

You dont say if its is a 2 stroke or a 4 stroke. The jets in carbs for small 4 stroke engines are very small . 2 stroke jets not so bad

 

[steve66]

A fine wire is sometimes the only way unless you have an ultrasonic cleaning bath up your sleeve or a powerful airline.
Preferable though to use brass or copper ( eg fuse wire), rather than a steel wire such as a bristle from an ordinary wire brush.

The idle jet size on that size carb is around 0.3mm

 

[NickRobinson]

I use a standard lens off a defunct SLR camera (held to the eye 'backwards') as a jewellers eye piece to check removable jets.
If at home, a blast from my garage compressor sorts much.

 

[pmyatt]

My Mercury 3.5hp decided no to idle. When I start it i have go right away and at 1/3 power or more. Any less and she doesn't like it. Certainly won't idle.

I read elsewhere it might be a blocked jet as I've already dismantled the float chamber and cleaned several times. There are references to putting fishing wire through it in order to clean and then others say no never put anything through it.

Can anyone clarify before I embark on this?

Would counsel against any form of probe. If you can get ashore in a town and find a garage, get brake cleaner as it works works better than carb cleaner

 

[No Regrets]

I have used a wire bristle for years with no ill effects on thousands of two and four strokes.

 

[CLB]

I have used a wire bristle for years with no ill effects on thousands of two and four strokes.

Blimey, maybe that's why you got through so many outboards

 

[Tim Good]

You dont say if its is a 2 stroke or a 4 stroke. The jets in carbs for small 4 stroke engines are very small . 2 stroke jets not so bad

Yeah 4 stroke... I'll give it a go shortly

 

[VicS]

The idle jet size on that size carb is around 0.3mm

No problem finding a strand of copper wire then.... 5amp fuse wire just the ticket and ive a huge reel of that!

 

[RichardS]

An inline fuel filter will stop the problem happening again: http://www.ybw.com/forums/showthread.php?480190-Can-I-install-pre-filter-for-Yamaha-4HP-outboard

As this is a forum not everyone will agree.

Richard

 

[Muddy Boat]

You wont have anything small enough to poke through a 3.5hp idle jet onboard. Cant post a link atm but look on boats.net and you will see an exploded diagram of the carb. Blowing or sucking may do it otherwise its ultrasonic clean

I did mine (2.5hp) yesterday with a strand of a brush.

 

[steve66]

I did mine (2.5hp) yesterday with a strand of a brush.

Main jet or pilot jet?

 

[steve66]

No problem finding a strand of copper wire then.... 5amp fuse wire just the ticket and ive a huge reel of that!

Yes that should be thin enough. Would it be stiff enough though?

 

[Muddy Boat]

Main jet or pilot jet?

Pilot jet. Previous owner (or their 'mechanic') had stripped the head off the main jet so waiting for some left handed drill bits - Could explain why it cut out under load! ;-)

 

[steve66]

Pilot jet. Previous owner (or their 'mechanic') had stripped the head off the main jet so waiting for some left handed drill bits - Could explain why it cut out under load! ;-)

Well done...stands a chance!