2003 140 Johnson 4stroke runs great then starts to stall after 10 min. warm up...

[Macville]

I have a 2003 Johnson 140 4 Stroke. It runs great for about 10 to 15 minutes and then acts like its running out of fuel. I can keep it running ( at a low RPM ) and it will motor me in but if I try going to plane it wants to keep cutting out. If I wait a while and start the motor after it sits for a while I can get another 10 to 15 minutes out of it again. As I said the motor runs great from the outset. I can bring it all the way to 6200 RPM. If anyone has a comment I would sure appreciate any advice.

 

[Daviet]

Re: 2003 140 Johnson 4stroke runs great then starts to stall after 10 min. warm up...

Welcome to the forum.
Have not worked on many 4 strokes, but a couple of thoughts.
Are you loosing fuel pressure, do you have a primer bulb in the system, try pumping it and see if the engine picks up.
Does it sound like you are dropping cylinders, an ignition componet can overheat and fail, and when it cools off it runs properly.
Just a couple of thoughts, I am sure others with more knowledge will chime in and help you out.

 

[Toddboat]

Re: 2003 140 Johnson 4stroke runs great then starts to stall after 10 min. warm up...

some ideas...
1-motor overheating and going into safety mode until it cools down, possibly the alarm is defective and not sounding.
is the pee stream healthy? is the block getting hot enough to steam water that you put on it?
2-motor is flooding a bit, and when the fuel evaporates, it lets you run it again (possible needle valve in carb/s not sealing completely)
look down carb throats while priming the bulb. if fuel is leaking into carb throat, then you have a fuel leak creating a rich condition enough to flood the engine (perhaps not on all cylinders) check that all of the butterfly plates in the carbs are opening together (in sync). If one is not, it could explain a rich mixture in one cylinder. maybe when the boat loses power it is not running on all cylinders.
3-fuel pump faulty (prime bulb when motor hesitates so you become your own fuel pump) if this makes it pick up again, then replace fuel pump membrane or just replace the entire fuel pump.

 

[Macville]

Re: 2003 140 Johnson 4stroke runs great then starts to stall after 10 min. warm up...

Welcome to the forum.
Have not worked on many 4 strokes, but a couple of thoughts.
Are you loosing fuel pressure, do you have a primer bulb in the system, try pumping it and see if the engine picks up.
Does it sound like you are dropping cylinders, an ignition componet can overheat and fail, and when it cools off it runs properly.
Just a couple of thoughts, I am sure others with more knowledge will chime in and help you out.

Good advice I have checked primer bulb and seems to be solid. I happened to do a sea trial with two mechanics on board yesterday afternoon and as murphy's law would have it the motor would not act up.... I think the ignition component is very susspect or I may be working through some trash in the fuel. Thank you Daviet for taking the time !