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1972 Johnson 25 Idle issues

T

tinboatman

Member
I have a 1972 Johnson that has an idle issue where after you return from WOT the idle slowly continues to fall until the motor dies. I have checked the timing throttle advance and got it dead on and have set the idle mixture screw to the perfect point. I got a clear fuel line running from the fuel pump to the carb and their is some bubbles going through the line at idle but not WOT that I suspect could be causing the issue but I am not certain. Also whats weird is the idle mixture screw is set between 1/2-3/4 a turn out which seems a lot further in than it needs to be. If I screw it out any further than 3/4 turn out the motor dies and any further than 1/2 in I get the lean coughing. Any advice is appreciated because I am stuck and dont just wanna throw parts at it blindly.
 
The first thing that I would tackle is the air bubbles in the fuel line. I had that same issue on one of my motors. It ended up being a two part issue. My first issue was I had sold my OMC factory fuel line with one of my other motors and had just bought a generic brand hose for the motor. The problem was it was leaking at the motor connection. So I removed the aftermarket and off the hose and bought a factory Johnson Evinrude and that cleared up about half of the bubbles. The other issue came from the actual connection in the fuel tank. It had a clear plastic hose on the inside of the fuel tank and the connection was leaking air up top. Alleviated that issue and I have no more air bubbles in the fuel system. Also check for leaks at all connection points after the hose connection on the motor by very very gently squeezing the primer bulb and looking for leaky connections. On my old 6 hp Johnson it was leaking at the fuel pump connection the cork gasket. It looked find to use but it had started to dry up and separate the cork. So I ended up changing out that gasket for the newer rubber style and that issue in a way as well.
 
I know the tank and fuel line on my motor is good because I also use them on and 6hp evinrude I have and it works perfectly fine. I had previously replaced both the internal fuel lines and fuel pump on that outboard, so today I went ahead and put hose clamps on all the lines instead of those factory fuel clamps that dont get that tight. Also the throttle had a lot of play in it so I got that fixed. After doing both those things it seems to be running a whole lot better but it still dies after idling for too long, but keep in mind it takes a whole lot longer maybe 3 mins now. The motor does still occasionally miss at idle. Also the farthest I can go down on the throttle cam before it dies is right at the 2nd mark and it seems like it should go down farther before the rpms drop to where it dies. There is still bubbles in the line but its not near as bad. Might just buy another pump because that cheap Chinese pump I put on it could have an air leak somewhere. I also have replaced points and condensers in the motor and set them to 20 thousands, and I have previously cleaned the carb but have yet to rebuild it.
 
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