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Old 04-07-2011, 10:37   #1
TOM
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Outboard Not Running

I have a problem with our 15 hp yamaha outboard,made all the more annoying because we are at Black River Mauritius .We came here as it is a great place to swim with the dolphins which we will not be able to do unless i can get the outboard going. It was working fine in Chagos ,has not been started for 4 weeks whilst we have been at the marina at Port Louie.
Problem is as follows, Starts and runs on half choke at two thirds trottle but when i bring it back to idle it cuts out .When i shut off choke it also cuts out .
I did find a bit of water in the fuel so i put fresh fuel in ,and drained the carburettor .i also changed the plugs .It is not starved of fuel as it runs happily on half choke at two thirds trottle. The motor is just over a year old .
Any advice or ideas on what to do would be appreciated.
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Old 04-07-2011, 10:43   #2
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Re: Outboard not running

My 8HP Yamaha was exhibiting exactly the same problem last week when I launched the dingy (after the gas from last year had been sitting on deck all winter/spring). My neighbor has exactly the same engine and had exactly the same problem. You should have seen the amount of water removed from our tanks. Never seen so much.

So, double-check the fuel system.

Often, outboards which won't idle have a blockage in the extremely tiny hole which feeds gas when idling. You can't believe how small it is...you need to hunt up the tiniest needle in the Admiral's sewing kit and clean that puppy out.

Needless to say, you need to be absolutely paranoid about the cleanliness of your fuel.

Good luck

Bill
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Old 04-07-2011, 11:52   #3
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Re: Outboard not running

Quote:
Originally Posted by btrayfors View Post
My 8HP Yamaha was exhibiting exactly the same problem last week when I launched the dingy (after the gas from last year had been sitting on deck all winter/spring). My neighbor has exactly the same engine and had exactly the same problem. You should have seen the amount of water removed from our tanks. Never seen so much.

So, double-check the fuel system.

Often, outboards which won't idle have a blockage in the extremely tiny hole which feeds gas when idling. You can't believe how small it is...you need to hunt up the tiniest needle in the Admiral's sewing kit and clean that puppy out.

Needless to say, you need to be absolutely paranoid about the cleanliness of your fuel.

Good luck

Hi Bill,



Bill

Thanks Bill , Not sure what you mean re the little tiny hole can you please expand on this .
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Old 04-07-2011, 11:58   #4
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Re: Outboard not running

i liked using in line filters in my outboard fuel system so i didnt have to get my carb overhauled every 2 weeks, as i did before the addition of that inexpensive lil item....
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Old 04-07-2011, 12:20   #5
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Re: Outboard not running

Kinda sounds like a carb problem with fuel that either has ethanol or deposited varnish. Four weeks can sometimes be enough to cause problems. Can you disassemble and clean the carb or find someone around you that can? I had the same problem on a motorcycle and ethanol fuel and the carb were the culprit. The mechanic claimed that ethanol fuel was the main reason he was still in business. I also learned that standard fuel stabilizer (red) did nothing for ethanol which required a different stabilizer (blue). Since switching over, I've not had any more problems.

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Old 04-07-2011, 12:28   #6
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Re: Outboard not running

Quote:
Originally Posted by zeehag View Post
i liked using in line filters in my outboard fuel system so i didnt have to get my carb overhauled every 2 weeks, as i did before the addition of that inexpensive lil item....
Yes i agree in line filters are a good idea .But has not having one caused my problem.
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Old 04-07-2011, 12:44   #7
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Re: Outboard not running

PROBLEM 1: OUTBOARD ENGINE IDLES ROUGH AND STALLS
PROBLEM 2: OUTBOARD ENGINE RUNS UNEVEN OR SURGES
PROBLEM 3: OUTBOARD ENGINE WILL NOT ACCELERATE

POSSIBLE CAUSE ➥ CORRECTIVE ACTION

fuel tank air vent closed or restricted ➥ check - air vent must be open all the way and free from restrictions

a pinched, cut or restricted fuel line; also loose fuel line connection ➥ check all fuel lines and replace as needed; check and tighten all fuel line connections

a dirty or restricted fuel filter ➥ check, replace or clean all fuel filters
restricted filter in fuel tank clean by rinsing in clean lead-free gasoline or kerosene

improperly mixed fuel; contaminants (water. dirt, etc.) in fuel ➥ check fuel and replace if necessary

an inlet needle (in carburetor) that is either stuck open or closed. (A needle that is stuck open will cause a flooding condition. A needle that is stuck closed will prevent fuel from entering carburetor.) ➥ remove and replace with new inlet needle

incorrect idle mixture adjustment ➥ re-adjust

damaged fuel pump diaphragm ➥ replace

carburetor is loose ➥ tighten bolts securely

chamber cover leaking air ➥ tighten or replace gasket

off idle holes plugged ➥ blow out with compressed air

main nozzle or idle nozzle air bleed holes plugged ➥ blow out with compressed air

improper main jet or restricted jet ➥ clean or replace with proper jet
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Old 04-07-2011, 12:46   #8
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Re: Outboard not running

Quote:
Originally Posted by TOM View Post
Yes i agree in line filters are a good idea .But has not having one caused my problem.
Yes, probably so.

To fix this, you will want to remove the carb. Be mindful of the little plastic clips that hold the linkage on, they swing out of the way, but don't pop off unless you swing them out first.

Draining the carb was a good try, the problem is that you have two jets in that the fuel passes through. The main jet (closest to the center) is likely clear, but the pilot jet is probably clogged.

As other posters have said, this jet has a TINY hole through it...

To get to it, remove the float bowl (the cup on the bottom of the carb).

Remove the screws and tap it with a plastic screw driver handle to loosen the seal on the gasket.. you probably don't have a spare so be gentle.

Once the bowl is off, the float and the needle valve will want to fall out... the pin that holds them in place is famous for falling on the ground, deck, or down your cockpit drains... be careful.

THe pilot jet is a small brass tube with a slot in the top that will come out with a streight screwdriver.

Find the 'smallest needle' you can find, maybe a really fine wire...

push through the jet from the slot side.. whatever is lodged in there came in from the thread side... you MAY be able to blow it out with a can of something compressed... but you will more likely need to push it out.


In my experience, this is about 90% likely to be the cause of the problem you mention.

Just as others have already said, this is not an uncommon problem.

Good luck!
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Old 04-07-2011, 12:47   #9
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Thumbs up Re: Outboard not running

Thanks Gord!

I was going to try to find an exploded diagram after I posted....



Good man!

Quote:
Originally Posted by GordMay View Post
PROBLEM 1: OUTBOARD ENGINE IDLES ROUGH AND STALLS
PROBLEM 2: OUTBOARD ENGINE RUNS UNEVEN OR SURGES
PROBLEM 3: OUTBOARD ENGINE WILL NOT ACCELERATE

POSSIBLE CAUSE ➥ CORRECTIVE ACTION

fuel tank air vent closed or restricted ➥ check - air vent must be open all the way and free from restrictions

a pinched, cut or restricted fuel line; also loose fuel line connection ➥ check all fuel lines and replace as needed; check and tighten all fuel line connections

a dirty or restricted fuel filter ➥ check, replace or clean all fuel filters
restricted filter in fuel tank clean by rinsing in clean lead-free gasoline or kerosene

improperly mixed fuel; contaminants (water. dirt, etc.) in fuel ➥ check fuel and replace if necessary

an inlet needle (in carburetor) that is either stuck open or closed. (A needle that is stuck open will cause a flooding condition. A needle that is stuck closed will prevent fuel from entering carburetor.) ➥ remove and replace with new inlet needle

incorrect idle mixture adjustment ➥ re-adjust

damaged fuel pump diaphragm ➥ replace

carburetor is loose ➥ tighten bolts securely

chamber cover leaking air ➥ tighten or replace gasket

off idle holes plugged ➥ blow out with compressed air

main nozzle or idle nozzle air bleed holes plugged ➥ blow out with compressed air

improper main jet or restricted jet ➥ clean or replace with proper jet
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Old 04-07-2011, 13:32   #10
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Re: Outboard not running

Please let us know if you get that thing running good again and what you did to make it work.
If your engine runs ok at half-choke it definitely is a fuel starvation problem so it definitely is in the fuel system. Gord has a really nice trouble-shooting tour.
kind regards,
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Old 04-07-2011, 14:11   #11
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Re: Outboard not running

Quote:
Originally Posted by TOM View Post
Thanks Bill , Not sure what you mean re the little tiny hole can you please expand on this .
If you look in the area of the throttle plate you should see about three small openings on the upper part of the throat. The one closest to the engine is the idle port and the others are called off idle ports. The off idle ports provide fuel when going from idle to full throttle since there is a dead band before the main jet begins to provide fuel. It is quite common for these small ports to clog and compressed air is usually the best way to clear them.
Some of the newer carbs actually control the air rather than the fuel delivered at idle but the end result is the same.
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Old 04-07-2011, 15:03   #12
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Re: Outboard not running

GORDY,

You are really the man with all the answers, I don't know how we would survive without you to constantly search and find the answers to all our questions....
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Old 04-07-2011, 16:03   #13
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Re: Outboard not running

Tom, I had the exact same problem with my 15 hp Yamaha a couple of years ago. It was the small jets in the carb but nothing I did cleared them out. I finnally took it to a Yamaha shop where the mechanic put the carb in an ultrasonic cleaner overnight and blew out the jets the next morning. Problem solved. If you can find an onld fashoned can of carb cleaner, the kind with a basket and closable lid, you might try taking your carb apart and soaking it over night. If you can find a local outboard mechanic with an ultrasonic cleaner it would be even better. If you can't do that a can of spray type carb cleaner sprayed through all of the jets might work, but it didn't on mine. Good luck.
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Old 04-07-2011, 22:21   #14
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Re: Outboard not running

I had a similar sounding problem with my honda 2hp,cleaned carby 3 times,finally found water sitting in low point of the feul line near the carby.There was only a drop of water in the carby.
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Old 05-07-2011, 10:46   #15
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Re: Outboard Not Running

Thanks for all the advice.I took the carbi apart this morning ,funny thing is it looked realy clean .Another aussie cruiser lent me his can of carbi cleaner and we gave it a good blast. It is now running again . I will have to keep a couple of cans of this stuff onboard.

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