I know I'm going to take a lot of heat for this...
DON'T DO IT!!!
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There will be no more carbon buildup in the combustion chamber than the thermal expansion and contraction will allow.
The carbon build up that hurts performance the most is on the backs of the valves, Intake valve in particular.
Pouring more oil to become carbon sludge build up on the backs of the valves won't help this situation in the least...
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There is nothing in your combustion chamber that a little WATER won't get loose...
Water turns to steam, and is not a killer of mufflers and catalytic converters...
If you use an old windshield washer tank, pump and spray nozzle pointed down the carb throat, it will work just like the expensive water injection systems, and can be done as you drive down the road with the engine at full temperature and operating speed...
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If you do the old dirt farmers trick of pouring any kind of oil down the carb throat, very bad things can happen...
First off, the air bleeds, vents, venturi outlets, and transfer slots were never meant to have oil poured on or in them...
Secondly, as the oil hits the back of the hot valves, it turns to coke, and then to hard carbon.
You are actually causing more of the problem you are trying to solve...
Third, you may pour too much, and hydraulic damage the piston, valves, rings, or rod bearings...
Fourth, you may plug your muffler, or you may kill your oxygen sensor or catalytic converter....
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Your exhaust system doesn't need oiling.
Keep the transmission oil in the transmission where it belongs.
"I Have The Body Of A God... Buddha"