yamaha 2.5 stalls when opening throttle

thomashoebus

thomashoebus

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When I open the throttle of my yamaha 2.5 hp outboard the engine stalls. When the gear is engaged the engine dies. When the gear is not engaged the engine stalls when opening the throttle and goes to normal again after the initial stall. When I open the Choke 1/3th everything is normal when opening throttle gear engaged or not. This suggesting that there is someting wrong with the mixture? The temperature of the engine is ok. When the engine is in free run the revolutions and the sound of everything is fine.

I cleaned the carburator already a few times and cleaned the nozzle in the carburator with a copper strand.
 
thomashoebus said:
When I open the throttle of my yamaha 2.5 hp outboard the engine stalls. When the gear is engaged the engine dies. When the gear is not engaged the engine stalls when opening the throttle and goes to normal again after the initial stall. When I open the Choke 1/3th everything is normal when opening throttle gear engaged or not. This suggesting that there is someting wrong with the mixture? The temperature of the engine is ok. When the engine is in free run the revolutions and the sound of everything is fine.

I cleaned the carburator already a few times and cleaned the nozzle in the carburator with a copper strand.
Click to expand...

sounds like blocked jet
 
I agree the carb probably requires further cleaning.

I am not not familiar with Yamahas and you do not give the model year or any other details
Fairly recent 4 stroke ??

Or old 2 stroke
 
Last edited:
Assuming this is a two stroke engine that has been stood for a while.

If this is the case petrol will have evaporated in the carb leaving an oily gum that, well, gums up the works.

An easy fix is to empty the tank and fill with raw petrol. Remove the plug top, pull raw petrol through the engine (please do not start it) whereupon the gum should desolve in the neat petrol. It may take one or two overnight soaks but the method has worked for me.

73s de

Johnth
 
I assume that this is the model with the integral fuel tank? Sounds like a major fuel starvation issue, check pipe and filter and fuel cock by removing pipe from carburettor end and turning on tap briefly, does fuel run out freely? If not, deal with that.

Next, check carburettor float chamber with carb off engine connect to fuel pipe and turn on for a few seconds. Then turn off and disconnect pipe and without inverting carb unscrew float chamber - it should be nearly half full.

Now check petrol gets into float chamber - connect with chamber off carb and turn on fuel briefly, check float operation, fuel should flow freely, and stop when float gently lifted. If not, change needle valve as it is faulty.

High speed jet is the main jet in the middle of the float chamber (usually)- check it is clear.

Finally, with engine running in a tank or dustbin,, adjust idle screw, normally screw fully in, back out 1 1/2 turns then carefully screw out or in to get the "null" point where revs are highest, set to centre position between the two points screwing in or our slightly where revs just begin to drop. This jet is what enables the engine to build from tick-over upwards until the main jet takes over.
 
I know this well....

Early models had slightly tempramental carbs and I BELIEVE that these were changed, a jet I think, but dont quote me...

If it is not this then the other thing is that these four strokes (straight petrol so 'mixture' problem should occur) dont like opening up too quickly. Unlike a 2-stroke that you can 'floor it' you have to accelerate from idle slowly initially.

The other thing is to check the slow running jet and the lean rich setting...
This though is a job for a technician who has the Yamaha data settings...if you have removed these screws and they are not back withing their tollerances then the engine wont run properly.

Speak to a yamaha dealer, check the yamaha website for dealers, id say...
 
thomashoebus said:
When I open the throttle of my yamaha 2.5 hp outboard the engine stalls. When the gear is engaged the engine dies. When the gear is not engaged the engine stalls when opening the throttle and goes to normal again after the initial stall. When I open the Choke 1/3th everything is normal when opening throttle gear engaged or not. This suggesting that there is someting wrong with the mixture? The temperature of the engine is ok. When the engine is in free run the revolutions and the sound of everything is fine.

I cleaned the carburator already a few times and cleaned the nozzle in the carburator with a copper strand.
Click to expand...

Have you tried changing the plug?
 
Sounds like a major fuel starvation issue, check pipe and filter and fuel cock by removing pipe from carburettor end and turning on tap briefly, does fuel run out freely? If not, deal with that.
Click to expand...
Worth checking out but if it was fuel starvation it would run ok for a minute or so and then peter out as the bowl empties wouldn't it?

If it idles Ok then the idle mixture setting should be Ok. Maybe it has a high speed mixture adjust as well if so that could be out.

Always a good idea to fit a new plug, I agree. Often seems to fix things that are seemingly unrelated!
 
it's a 4 stroke yamaha model 2003. I Changed prop and dog clutch last winter. But this problem is unrelated since the outboard had the problem already 3 years before but less outspoken.
 
Well certainly, as everyone has said, its likely to be a problem of weak fuel air mixture once you get past the idle jet rev range. That could be a partially gummed up jet. Modern fuels evaporate and leave gum behind, and prodding with a copper wire wont necessarily clean this out sufficiently. Get yourself a container of carb cleaner and soak the carb in it before blowing clear with high pressure air. The fine passages in the carb body are the key ones. Then make sure the float level is correct.

Some carbs have an accelerator pump which squirts a small jet of petrol into the butterfly area to get over initial mixture weakness when the butterflies are opened but air velocity is insufficient to take enough fuel through. If your carb is like this then check that the pump is working correctly - fill the bowl with petrol and hand operate the throttle.
 
Speak to your yamaha dealer...I am fairly certain this year of 2.5 had the problematic carburettor....I think they did soemthing to fix them....but speak to them and check it out.

Dont mess about with adjusting the jets and mixture screws and things without knowing what the settings should be.
 
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