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08 Tohatsu 6hp Black oxidation inside the spark plug

A

AVID_FISHERMAN

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I'm having issues starting and maintaining my outboard. It starts and stalls within seconds. It takes a few pulls and pauses before maintaining it's idle. I removed the spark plug and noticed that there's a black oxidation at the tip of the spark plug and where it sits. Does this mean that my carburator is running lean. If so, do you have any website or instructions on how to fix or adjust the lean. Your response is greatly appreciated. Thanks in advance.
 
Black is not lean, but rather rich. A little carbon on the metal case of the plug is normal. That carb is non-adjustable, but if you are having idling issues, you probably need to send the carb to the carb dip bath.
 
Are you having any cooling issues? My 8 HP blew the head gasket after 8 - 10 hours. The plug at the blown cylinder had a black deposit on it too.

Stick the engine in a barrel, remove the thermostat cover and thermostat. Start the engine. If you have exhaust in your water flow, and pulsing from the thermostat port, you too may have a blown head gasket.

If not, you may want to have your head bolts re-torqued anyway. When I removed my head the bolt tightness was all over the map. The loose ones were where the gasket blew (top cylinder). This was a 2010 engine!

Seems like poor quality control!
 
PABOATER1949 said:
Are you having any cooling issues? My 8 HP blew the head gasket after 8 - 10 hours. The plug at the blown cylinder had a black deposit on it too.

Stick the engine in a barrel, remove the thermostat cover and thermostat. Start the engine. If you have exhaust in your water flow, and pulsing from the thermostat port, you too may have a blown head gasket.

If not, you may want to have your head bolts re-torqued anyway. When I removed my head the bolt tightness was all over the map. The loose ones were where the gasket blew (top cylinder). This was a 2010 engine!

Seems like poor quality control!
Click to expand...

I'd say! Good thing that it's still under warranty for your sake. I'll pick up a service manual this weekend and see if I can clean the carburetor first of all and if that doesn't work perhaps go with your option. Thank you for your response.
 
Before you go pulling the stat, etc., consider that you can diagnose a head gasket problem (very rare on the MFS4/5/6), with a compression test and a leak-down test. Bear in mind that the cooling system will indeed contain exhaust... on a good powerhead... if the cooling water flow is low, because of the common water and exhaust exit. Not unusual to see exhaust coming out of a telltale port if the inpeller is blown... So that method to check for compression leakage is a "maybe" diagnostic.
 
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