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Honda 9.9 Vomits Dirty Fuel from the air horn but carb is clean???!!

J

jpendoley

New member
Hi, new forum member here with a strange one. My BZBC 9.9 has one year on it, fresh oil and fresh gas. It was running fine until last night when it shutdown abruptly and an oily fuel mixture flows out of the air horn. The gas going in is very fresh and the filter is clean. If I drain the carb and refill it with clean gas, it starts up ok and then starts to run rougher and rougher. Finally, it shuts down and a brown mixture that smells like gas flows out of the air intake. I took the carb off and eyeballed the float-it looks squeaky clean. I see a hose that leads from the air horn to a structure that has other hoses running out of it to the other side of the engine. Can anyone give me some ideas?
Any suggestions much appreciated.
Jim
 
Well, the hose you see going to the other side of the engine is from the crankcase breather assembly. It is very likely that there is "dirty oil" in there. The breather, at least on the later models, is part of the "head cover" (valve cover). See item 6 in the link below.

http://www.boats.net/parts/search/H...Later/BFP9.9DK0 LRTA/CYLINDER HEAD/parts.html

If your engine suddenly developed an inordinate amount of crankcase pressure it could force any pooled oil in that line into your "muffler cover" (air horn).

Try running the engine with the oil filler cap removed. Place a rag over the opening before you start it. A normal amount of crankcase pressure should try to lift the rag up at idle but generally not blow it off.

Excessive pressure will likely blow the rag up into the air and spray oil droplets everywhere.

This is "good old boy" diagnostics and is subject to some interpretation but it should give you an idea of why so much liquid is in your muffler.

Another possibility is that the carb float is stuck wide open and she's flooding out badly. Sometimes tapping the bottom of the carb with the handle of a screwdriver will "unstick" a float......
....if you're lucky.

Good luck and let us know what you find.
 
I agree with all that Jimmy said plus...the oil level may be too high. It should be about 1/4 " below the full mark.

Also...be sure that you are using a Honda oil filter for that motor.

Mike
 
jgmo said:
Well, the hose you see going to the other side of the engine is from the crankcase breather assembly. It is very likely that there is "dirty oil" in there. The breather, at least on the later models, is part of the "head cover" (valve cover). See item 6 in the link below.

http://www.boats.net/parts/search/H...Later/BFP9.9DK0 LRTA/CYLINDER HEAD/parts.html

If your engine suddenly developed an inordinate amount of crankcase pressure it could force any pooled oil in that line into your "muffler cover" (air horn).

Try running the engine with the oil filler cap removed. Place a rag over the opening before you start it. A normal amount of crankcase pressure should try to lift the rag up at idle but generally not blow it off.

Excessive pressure will likely blow the rag up into the air and spray oil droplets everywhere.

This is "good old boy" diagnostics and is subject to some interpretation but it should give you an idea of why so much liquid is in your muffler.

Another possibility is that the carb float is stuck wide open and she's flooding out badly. Sometimes tapping the bottom of the carb with the handle of a screwdriver will "unstick" a float......
....if you're lucky.

Good luck and let us know what you find.
Click to expand...

thanks for the suggestion-I will try the rag test, but assuming I do have excessive crankcase pressure, what would cause it? also, I mistakenly indicated it was a 9.9 its not, its an 8 HP. Sorry for that confusion. the manual calls for 800 mls of oil-but that seems to overfill it-would it be too risky to run it with less say 700 mls?
 
Yes, as hondadude teaches us all, run your oil level halfway between the full and add lines on the dipstick.

Watch out for your outboard "making it's own oil". Which means the oil level will increase on it's own without you ever adding any.

What happens in that case is that the thermostat is stuck open and not allowing the engine to reach operating temperature. This can result in poor combustion and incomplete burning of the fuel. The unburned gas finds it's way down into the oil sump, raising the oil level and contaminating and diluting the oil. When this happens, it needs immediate correction to prevent engine bearing damage.

The 8 h.p. and the 9.9 are close enough "cousins" that the information will apply equally for both.

Excessive crankcase pressure is usually the result of combustion gases getting past broken or stuck piston compression ring. Although, it can also be the result of a damaged piston such as one with a hole in the crown from detonation or breakage in the combustion chamber and, many times, this is a result of valves contacting the piston due to jumped timing.

A cylinder leakdown test is needed to identify which cylinder and the severity of the leak.
 
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