mercury 2.5 choke needed all the time

[bugs]

While changing my spark plug solved my recent starting problem (thanks again), I now find I need to use the choke all the time to keep it running. I have to keep it at about half way and twiddle with it a bit to prevent it from stopping. I dismantled the carb since I understand the needle can get sticky, all seemed clean but the problem persisted. Any ideas on what might be causing this

 

[steve28]

This is normaly due to bad fuel, water etc.
The way i fix mine is to run it as near to full throttle as you can and then turn off the fuel whilst doing this, carry on and wait until the fuel runs out which is normaly 30 seconds.
You should be able to just turn the fuel back on and carry on as normal.
Failing this you need to check the carb again paying attention to the jets.


steve

 

[bugs]

Thanks Steve,
I'll try that. The tank was dry when I cleaned the carb so it got fresh fuel. Perhaps a more thorough cleaning is needed.

 

[Evadne]

I used to get this on my old Lambretta, and it was nearly always a blocked fuel jet. Dismantle the carb, blow through the jet(s) and reassemble. You can get quite good at it after a while!

 

[cliff]

[ QUOTE ]
While changing my spark plug solved my recent starting problem (thanks again), I now find I need to use the choke all the time to keep it running. I have to keep it at about half way and twiddle with it a bit to prevent it from stopping. I dismantled the carb since I understand the needle can get sticky, all seemed clean but the problem persisted. Any ideas on what might be causing this

[/ QUOTE ]Wax, dirt and or general gunge in the jet or spark gap incorrect. Assuming you have gapped the plug correctly before fitting you could try starting the engine and running it at full speed then flipping the choke on and off quickly a few times and or doing same with throttle.

The carb in the 2.5's is rather simple so very little to go wrong. Failing the above trick with the choke and throttle you would probably be better to remove the carb then remove the float bowl and jet needle and blow the carb out with an air line. It is a good idea to run the carb dry after each use (before lifting back on board) as ocne the fuel evaporates there is a residue left which can build up and eventually cause a restriction in the jet. Another thing to check is the slow running adjustment.
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“Artificial intelligence is no match for natural stupidity”
Skype id:cliffillupo

 

[KeithH]

I agree with the other posts - likely to be a blocked jet in the carb. We had exactly the same phenomenon with a Yamaha 4 - a jet was completely blocked with gunge, so the engine needed the choke almost closed to get some fuel through the carb. A full cleaning of the carb fixed the problem - though some of these small jets are not easy to clean if blocked up with waxy material.

I also agree with the suggestion of running the carb dry after use. Does seem to reduce this risk.

 

[Lakesailor]

You can get a carb cleaning fluid to remove the petrol residues.
It is almost definitely a blocked main jet.

 

[tross]

In addition to all of the above, make sure you have reassembled the float and needle valve correctly - this can cause low fuel level in th efloat chamber which weakens the fuel / air ratio.

 

[ShipsWoofy]

Please come back and report if you solve the problem, it is always good to have other peoples knowledge in the armoury for those running the same motors.

I let mine run out of fuel on Monday night in the middle of the harbour, about 3/4 of the way to the slip. Sculled in on a mirror calm. Just means I have to scull out to the boat on Friday for fuel...here's hoping for good weather!

 

[snowleopard]

I believe this engine, like the mariner, is a re-badged tohatsu. If you have taken the carb apart it is possible to reassemble incorrectly. The float has a hole through the centre to clear the jet assembly and there is a slight taper to the hole. You need to check the wider end of the hole is at the top or it can stick on the jet tube.

 

[steve_cronin]

So, is it refusing to run at all without the choke?

or is it just on idle?

On this engine the main jet has a vertical needle which is moved up and down in the jet tube at the same time as a piston moves up and down to regulate the air intake. Slow running is achieved through a by-pass around the bottom of the closed piston. This is regulated by the one and only adjustment available, a slot headed horizontal screw into the carburettor body. The initial default setting of this is two whole turns out from fully in. Set it to this, start the engine and adjust for tickover.
You might have re-assembled the carb. incorrectly but I doubt it unless you have allowed air to be introduced into the inlet tract somewhere. Is the carb fully home and the pinch bolt tightened?

Without actually seeing the beast, it is difficult to give an accurate diagnosis. One thing I will tell you about that engine (& I know it well having previously owned one for fifteen years and having just bought a new one - actually the 3.3 but it's identical in the powerhead design) is that you have, invariably to alter the float height to get the mixture right. They usually run too rich.

Steve cronin