kevin_stinton
New member
"I have obtained a 1971 25 HP
"I have obtained a 1971 25 HP Johnson outboard which seems to be running rich and producing much more smoke than I would expect it to (even for such an old engine).
The plugs soon become blackened and oily after running for a while, even though the mix is at the correct 50 to 1 ratio you would normally use on a two stroke outboard.
I am really struggling to understand how this could be still happening because I have recently fitted the following parts:-
A) Carburetor float, B) Float valve and seat, C) Gasket nozzle, D) Float bowl gasket, E) bridge needle valve (Idle circuit).
Pic 1"">
I have also cleaned out all of the air circuits with a pipe cleaner and high pressure air. I have also adjusted the angle of the Float arm (There doesn’t seem to be any other way to regulate fuel flow into the main jet.
In fact, if I bend the Float arm up any further, it stops letting in fuel altogether.
The only thing I thought might be affecting the fuel to air ratio, could be the depth that the main jet seems to be dipping into the bowl itself.
I have noticed an exposed silver grey section of the jet underneath that indicates to me that the Jet might have dropped out slightly by vibration or heat expansion and contraction over time.
Pic 2"">
Should the Jet protrude higher into the Venturi chamber than it does in the picture below? Should the top of the Jet be in the centre of the air flow?
Pic 3"">
The bottom of the main jet has holes drilled through the side.
I am assuming that this is to allow it to draw air into the tube along with fuel from the bottom, thus reducing the overall fuel air ratio coming out of the jet?
Am I correct in assuming that if the jet was to low into the bowl, or the fuel level is too high, more fuel than air would be pulled into the jet through these holes, resulting in an over rich mix?
Pic 4"">
Fig 1"">
Does anyone know how much fuel should be in the bowl when the float is correctly adjusted?
Another thing I have noticed is that there is a small restrictor valve (referred to as an orifice plug) between the inner and outer chambers of the main float chamber (see the diagram above).
Is this plug adjustable, or should it be so? If it is supposed to be adjusted somehow (the one in my carburettor bowl wont turn) would this be able to limit the amount of fuel coming out of the main jet?
What other purpose could this plug serve other than so restrict the flow of fuel into the inner chamber?
I am grasping at straws at the moment and am probably thinking along the wrong lines, so any advice would be much appreciated thanks."
"I have obtained a 1971 25 HP Johnson outboard which seems to be running rich and producing much more smoke than I would expect it to (even for such an old engine).
The plugs soon become blackened and oily after running for a while, even though the mix is at the correct 50 to 1 ratio you would normally use on a two stroke outboard.
I am really struggling to understand how this could be still happening because I have recently fitted the following parts:-
A) Carburetor float, B) Float valve and seat, C) Gasket nozzle, D) Float bowl gasket, E) bridge needle valve (Idle circuit).
I have also cleaned out all of the air circuits with a pipe cleaner and high pressure air. I have also adjusted the angle of the Float arm (There doesn’t seem to be any other way to regulate fuel flow into the main jet.
In fact, if I bend the Float arm up any further, it stops letting in fuel altogether.
The only thing I thought might be affecting the fuel to air ratio, could be the depth that the main jet seems to be dipping into the bowl itself.
I have noticed an exposed silver grey section of the jet underneath that indicates to me that the Jet might have dropped out slightly by vibration or heat expansion and contraction over time.
Should the Jet protrude higher into the Venturi chamber than it does in the picture below? Should the top of the Jet be in the centre of the air flow?
The bottom of the main jet has holes drilled through the side.
I am assuming that this is to allow it to draw air into the tube along with fuel from the bottom, thus reducing the overall fuel air ratio coming out of the jet?
Am I correct in assuming that if the jet was to low into the bowl, or the fuel level is too high, more fuel than air would be pulled into the jet through these holes, resulting in an over rich mix?
Does anyone know how much fuel should be in the bowl when the float is correctly adjusted?
Another thing I have noticed is that there is a small restrictor valve (referred to as an orifice plug) between the inner and outer chambers of the main float chamber (see the diagram above).
Is this plug adjustable, or should it be so? If it is supposed to be adjusted somehow (the one in my carburettor bowl wont turn) would this be able to limit the amount of fuel coming out of the main jet?
What other purpose could this plug serve other than so restrict the flow of fuel into the inner chamber?
I am grasping at straws at the moment and am probably thinking along the wrong lines, so any advice would be much appreciated thanks."
