johnson 9.9 black sludge & runs hot

[brokenjohnson9.9]

I have been fighting this little bugger for a while. 79 9.9 has sat for a few years. rebuild carb,new fuel pump,fuel can, and hose,new water pump impeller and thermostat. to fix a stalling problem at full throttle. changed plugs seems to run better, full throttle and idle speed BUT now it seems to run hot at the tell tail,and after a hour or so of running the exhaust ports are all black, the back of the boat at the water line is all black (sooty) the center of the prop has a black sludge comming out of it, and it will ooze this stuff for a few weeks. easy clean up with soft scrub but something is not right here. any ideas?
more detail if needed

Chuck

 

[Solittle]

Re: johnson 9.9 black sludge & runs hot

If it has not been run in a few years it may just need to be run for a while to get all of the crud blown out. What you describe is unburned oil from combustion. Do you normally run it wide open or at a slow trolling speed? And what plugs did you put in it?

 

[brokenjohnson9.9]

Re: johnson 9.9 black sludge & runs hot

Not to be evasive but both, I troll a bit once I make a full throttle run to my fishing spot. that usually takes 15 minutes to get there. I try to drift as much as possible an not load it up. I might just take a full tank O fuel, a cooler and run the thing for a solid day at various speeds and get it cleaned out. It smells oily when running, I tried to lean it out a bit but the temp out the tell tail has me a bit concerned. the plugs are the NGK replacement to the champions it had originally type escapes me I can find it if you like.

 

[HighTrim]

Re: johnson 9.9 black sludge & runs hot

First off you should keep the Champions in it, that is what it was meant to run on. There is a good thread in the FAQ about the black sludge that you are describing that you should read. When was the impeller last changed? Cheap part for very expensive if it fails. I would look into that.