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Honda 9.9 black soot in exhaust

F

Fishability

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I replaced the carb, run clean gas and I still have this black soot coming from exhaust. This is after running at low speed for 8 hours.
 
Gotta be running rich, or does it use any oil? Does it run smooth at all speeds? Will it start cold without choking it? What year is it? Might be low compression too. Thermostat? Running too cold could cause this problem too. Shoot it with an infrared gun....see what you get.
 
I agree that it could be running cold and, thus, combustion would be inefficient causing unburned fuel to mimick a rich condition. When was the last time the thermostat was replaced? This is a once about every 4 years chore that usually gets "bypassed". But some Tstats go bad much sooner than that and engine operating temperature should be checked anytime an issue like this crops up.

Good luck.
 
And don't even consider running without a t-stat. That's an excellent way to stick the rings, which soon leads to loss of compression.
 
timguy said:
Gotta be running rich, or does it use any oil? Does it run smooth at all speeds? Will it start cold without choking it? What year is it? Might be low compression too. Thermostat? Running too cold could cause this problem too. Shoot it with an infrared gun....see what you get.
Click to expand...

Does not use oil. It does not always run smooth. 2004. Hard to start cold. Will change stat first.
thanks
 
Hard starting and not running smooth are both signs that the carbs need attention. Sooty exhaust reinforces that call. Makes no difference when they were cleaned last, they're due for some attention again (or still?)....
 
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