2002 Mecury 2.5hp Carburetter flooding.

[sailorsyd]

Hi all!
I can usually manage to sort things out on my own, but I've run out of ideas with this one !
My friends outboard is flooding while on tickover and while stopped. He has to turn the fuel supply off to prevent constant drips.
New OEM needle valve and seat fitted, new OEM float fitted. New gasket fitted to float chamber. No dirt on, or upstream of the needle valve assembly. Float lever arm pivot and pin are all free with no burrs or projections that could foul movement. I have adjusted the float lever arms by small degrees, from the float being level with the float chamber gasket (when inverted), to so low that no fuel flows at all.(I don't know the correct setting for fuel level adjustment, but it's not usually that critical)
With the float bowl removed the needle valve stops fuel flow with the lightest touch. The arms of the float lever are set equally. No cracks are apparent in the Main Jet housing and no burrs detected that could jamb the float. Gentle tapping doesn't seat anything any better. Fuel can be seen actually welling up out of the needle valve in the ventury. This within a few seconds of turning on the fuel tap (flow is faster if throttle valve raised). I've worked on several motorcycle engines and have good knowlege of carburetters, but this carb is so simple it beggers belief that I can't fix it!! Is there a design fault - or am I missing something?
Engine runs fine under load and at higher revs. It starts easily from cold. When hot I need to turn off the fuel and open throttle until it fires up.
Was convinced it would be fuel ingress into the float, but this was the final part I replaced with no improvement!
Any ideas would be appreciated.
Cheers
Syd

 

[Yepblaze]

Re: 2002 Mecury 2.5hp Carburetter flooding.

Make sure the gasket washer was replaced on the seat when installed.

Without proper setting of the float level and float drop it is very common for it to not work right.

A bad or heavy float will also cause this problem. As will a porous carb body.

Perhaps it's time for you to buy a "carburator complete" or have it professionally repaired.

 

[sailorsyd]

Re: 2002 Mecury 2.5hp Carburetter flooding.

Make sure the gasket washer was replaced on the seat when installed.

Without proper setting of the float level and float drop it is very common for it to not work right.

A bad or heavy float will also cause this problem. As will a porous carb body.

Perhaps it's time for you to buy a "carburator complete" or have it professionally repaired.

Thanks for the quick reply Yepblaze.
Just checked the carb diagram. This model carb doesn't have a gasket washer fitted under the valve seating. I can see where you were coming from though!
I am satisfied that the valve shuts off at approx the right level by gently lifting the float while fuel on with float chamber bowl removed.
It still seems for all the world that the float hasn't enough buoyancy to close off the needle valve!(But float came brand new in a sealed packet!)

A porous carb did cross my mind as well, but the only area that could cause flooding from the throttle needle jet, would have to be the throttle needle valve and Main Jet tube. (It projects down into the fuel in the carb bowl). Having sealed this at the ventury end and pressurised the other end (via main jet) I have now ruled this out using the soapy water bubble test...

I think my friend would rather cut his losses and part exchange the engine before shelling out for a new carb! The new needle and seating with a gasket cost him ?75 ( I think they saw him coming... ) The float then cost another ?25 to import.

Surely it has to be something simple and easily repairable. It's become a challenge more than anything now!!!
If you have any more ideas Yepblaze, or if someone else can throw any light on this problem I would love to hear from them.
I wonder if this is a common fault on these carbs?

One thing that did occur to me was that the drilled out holes in the carb body for the float pivot pin could be slightly wrong.
If I was to re-drill these holes a little nearer to the needle valve it would have the effect of increasing the leverage applied to the needle. Have I explained that clearly?

I'll see if anyone else can help before getting the tiny drill bits out.
Many thanks again,
Syd

 

[TOHATSU GURU]

Re: 2002 Mecury 2.5hp Carburetter flooding.

There are two different carb kits available for that frame size engine. You may have put in the kit for the model from the early 90"s.

 

[sailorsyd]

Re: 2002 Mecury 2.5hp Carburetter flooding.

Thanks Tohtsu Guru,
The engine belongs to my friend. He obtained the parts from a dealership by presenting the carburettor along with the engine Serial No. I checked the parts Nos. against the diagram online showing an identical carb to the one I have. i.e for the 2002 year engine. I'm pretty sure the parts are correct. They matched the old parts exactly.
I have tried various float level settings, to no avail, but for the sake of correctness, do you know if the float lever arms should be level with the float bowl gasket when carb inverted?
Photo of carb attached.

..............................................................................

UPDATE;- See attached photo (with arrows)

I have altered the fulcrum point for the float lever arm to increase the leverage applied to the needle valve. From about 3:1 to about 5:1.
This was done by re-drilling the aluminium support posts for the lever arm pivot and re-drilling the lever arm itself. The lever arm holes were filled with solder first so that the new holes could be drilled further back (brings arm forward).
See photo. New holes indicated with blue arrows - new thin S/S pin indicated with Red arrows. Old thicker pin shown in position but discarded now.

Initial tests look good, but haven't had the motor running in water yet, due to lack of free time. Will update again when fully tested.

Syd



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[BigDaddyDave]

Re: 2002 Mecury 2.5hp Carburetter flooding.

Syd
I am having the EXACT same problem on the same carburetor, and I am very anxious to see if anyone comes up with the secret solution, because this is driving me crazy. I too put in a brand new kit with new float, needle valve, seat, etc. and I CANNOT get it to stop leaking. Yet when you remove the bowl and put the slightest pressure with your finger, it stops. It is as if the float just can't push up on the needle hard enough to shut off the flow, but that makes no sense seeing that this was the way it was designed. And after all it is just a gravity feed, so it doesn't take much at all.
I feel your pain.....and I hope someone knows the answer.
Dave