# yamaha 4hp stalls on idle



## fred1diver (Aug 17, 2013)

hey everyone, can someone help me out
my 2008 Yamaha 4 stroke 4HP runs great exept when I put it in low speed

any speed above starting speed (arrow on throttle arm) is fine, but at the arrow and below she stalls on me  
not to practical when trying to dock 
I checked the spark plug, added an inline fuel filter, brand new gas (high octane) 
even removed the carb to spray some carb cleaner...

the motor ran perfectly at the start of my season (bought her in july)
but since I drained the fuel to remove the motor for transport (trailer sailer)
she stalls on me
so now I want to fix that problem before the end of the season so I can get out a few more times and before I store her for winter
thanks in advance
FRED


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## Faster (Sep 13, 2005)

Sounds like a plugged jet in the carb, can you adjust the idle speed up a bit if that would help? These carbs are usually relatively simple, pull the jets and make sure they are clear, reassemble and try again.


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## Chas H (Sep 6, 2013)

It sounds like you may have a slightly plugged idle jet or even a dirty air horn/venturi. I had the same problem with my Tohatsu last month. Add a shot or two of Sea Foam fuel system treatment (it is real stuff and Sea Foam is its name) to the fuel tank. Start the engine at the dock and let it warm up. Spray some carb cleaner (Gumout, STP, CRC, etc.) into the air horn and rev the engine as you spray. If/when the engine begins to sputter badly, stop spraying and rev it up to keep it running. Repeat the process half a dozen times if you want to. Then see if it idles. It may also be helpful to adjust the idle speed. That is typically done with a screw that when turned moves a piece of linkage that opens or closes the throttle. Worse case you may need to disassemble the carb again and soak it in a tub of carb cleaner made for that purpose. Then wash all the parts with clear water and blow them dry (gently) with compressed air. If you do soak it remove all neoprene parts as they will be destroyed by the cleaner. One more thing, your manual will suggest which side the motor must be laid on if you do lay it down. It sux not being able to trust your kicker. Fortunately my marina allows us to sail into our slips.
-CH


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## jrd22 (Nov 14, 2000)

I agree with Fast, clogged idle jet. Take the carb apart and blow out the jets. Those engines are pretty fussy about fuel, especially ethanol.


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## Chas H (Sep 6, 2013)

I would not disassemble the carburetor unless other options do not fix the problem. Start with the simple options first then go deeper if necessary.
-CH


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## theartfuldodger (Sep 4, 2006)

I would suggest check the motion tube in the carburetor it most likely is block slightly common problem.


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## fred1diver (Aug 17, 2013)

thanks everyone, as soon as the rain ends, probably late tonight
I'll work on it and tell you my results
thanks again
FRED


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## dabnis (Jul 29, 2007)

No hands on experience with Yamahas but you might try this before pulling the carb apart. If there is a low speed mixture screw, not the idle speed screw, generally on or near the end of the cable fitting, run the motor speed up to a fast idle and open the mixture screw as far as you can. If it comes out the motor may die right away. If you can keep it running with the screw backed out, let it run for a bit.

Then, gently turn the screw back in until it stops, don't force it. Unscrew it about 1-1/2 turns out. Set the speed about as low as you can without it stalling and slowly continue to back it out until it starts to stumble. Then back in just enough to smooth it out. Set it as rich as you can without it running rough, rich is good.

Make sure the motor is well warmed up before starting the adjustment. If this doesn't work, off with the carb for a thorough cleaning.

All this assumes the vent is open, there are no air leaks in the hose or elsewhere and that the filter is clean.

Paul T


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## Mechsmith (Jun 7, 2009)

It's probably the fuel. Try some other brands first before you take anything apart.

Ethanol has less energy per unit volume. At idle the difference is such that the carb doesn't admit enough fuel to keep it running. Automobiles correct this electronically.

I have the same problem on my 2001 Yamaha 8 hp. We can't fix it except by overthrowing governments. That's too much of a project. I check to see if it will idle before I need it to idle. It does make it hard to get in gear though.


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## Mechsmith (Jun 7, 2009)

P.S. Altitude also will have an effect for the same reason.


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## joyinPNW (Jan 7, 2013)

We had the same problem a few years ago-a marine mechanic gave us some advice. Always run all the fuel out of the engine before turning it off (disconnect the fuel line) since the ethanol forms a gummy mess inside. It has never stalled since. And, if you can buy the ethanol free fuel, that's better, if not practical...


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## Faster (Sep 13, 2005)

joyinPNW said:


> We had the same problem a few years ago-a marine mechanic gave us some advice. Always run all the fuel out of the engine before turning it off (disconnect the fuel line) since the ethanol forms a gummy mess inside. It has never stalled since. And, if you can buy the ethanol free fuel, that's better, if not practical...


This is our standard practice as well.. Nissan 3.5 that gets little use but hasn't failed to start in 8 years.


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## dabnis (Jul 29, 2007)

joyinPNW said:


> We had the same problem a few years ago-a marine mechanic gave us some advice. Always run all the fuel out of the engine before turning it off (disconnect the fuel line) since the ethanol forms a gummy mess inside. It has never stalled since. And, if you can buy the ethanol free fuel, that's better, if not practical...


If you can get to it, it is better to drain the float bowl as "running it dry" leaves a small amount of fuel in the bottom of the bowl.

Paul T


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## fred1diver (Aug 17, 2013)

Mechsmith said:


> It does make it hard to get in gear though.


it sure does, which make me look bad when I'm docking, but even worst, forces me to repair the bow


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## fred1diver (Aug 17, 2013)

joyinPNW said:


> We had the same problem a few years ago-a marine mechanic gave us some advice. Always run all the fuel out of the engine before turning it off (disconnect the fuel line) since the ethanol forms a gummy mess inside. It has never stalled since. And, if you can buy the ethanol free fuel, that's better, if not practical...


the fuel I use it high octane without ethanol, my problem started after I ran the engine dry, I'll try to run it dry again


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## dabnis (Jul 29, 2007)

I have used this for many years in many kinds of engines and have not had any fuel related problems except for the time I forgot to drain the carb over the winter:

Berryman® B-12 Chemtool® Carburetor, Fuel System and Injector Cleaner | Berryman Products

Other brands may be similar.

Paul T


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