1998 Johnson 150 Ocean Runner will not idle when engine warms up.

[Jose67]

Need some guidance / opinions on what is causing this engine not to idle when it has warmed up. It will stay running when cold started and after making a run at near full throttle it will come back down to an idle and stay running. After I turn it off and let it sit for a few minutes I can crank it back up and after 5 seconds or so when the quick start circuit brings the idle back down it will almost immediately turn off, I have to fast idle it at 1200 rpm to keep it running. Here is a list of things that I have done but has not corrected the problem. 1. Rebuilt carbs and sprayed out throttle plates, used new gaskets and seals that were removed, still same issue. 2. Replaced port side temperature sensor, still same issue. 3. Replaced power pack, optical sensor and plug wires with new CDI Electronics parts, thought that fixed the issue because it idle good while running on muffs but after I put it in the water made a run at near full throttle turned it off for a few minutes and cranked it back up same issue, have to fast idle it so it will stay running, made a near full throttle run back to boat ramp throttle down and it stays running at idle but once I turn it off and crank it back up after the quick start circuit brings idle down it will turn off.4. I have checked fuel flow to pump by squeezing the primer bulb and by running engine with hose disconnected from carbs, both ways there is good flow just don't know what the fuel pressure is.5. Removed carbs and throttle plates to double check gaskets and check reed valves, everything looked good. I am stumped on if this is a fuel or electronic issue. Engine runs great once I get passed the low rpm issues. I feel I am just throwing money at this thing, my next item on the list was to check fuel pressure and possibly buy a new fuel pump. Need some guidance on where to go from here. One interesting thing that I have observed is that the primer bulb does not get hard, I can squeeze it several times and see the fuel line move at the fuel pump but it does not get hard or neither do I see where the fuel is going if anywhere, it is not overflowing the floats.

 

[Chris1956]

Well, it sounds like you need a new primer bulb. I doubt that will fix your issue.

I have the same motor and issue, and have no fix for it. It has been suggested that heat soak may be the cause of the warm restart problem. On my motor, if you let her sit a couple of hours, or the water is colder, she will restart w/o issue. It is only when you run her, shut her down and restart within an hour, especially when the day and water are warm..

My mitigation is to use throttle only to run the motor in neutral at 1200 (or so) RPM, until she runs smooth. It only takes a couple of minutes at that RPM, and then she behaves normally.

I would be interest to see if anyone else has a fix.