alecsammy

I took the engine apart , heat exchanger leak and noticed alot of carbon on the pistons . I'm running a thunderbolt -4 ignition the plugs are not showing any signs of running rich . I'm actually running lean on the top end due to low fuel pressure. This is a gen-6 502 carb with about forty hours on it. I'm running mid grade fuel and the engine runs excellent. What causes this to happen. The engine has a holley 800 marine rpm air gap and dart heads the compression ratio is about 8.4:1 and a crane 731 cam. Thanks Alec

Velocity Vector

iTrader: (4)

Through the introduction of contaminents such as oil or overly rich air/fuel ratios, carbon build-up can become excessive.

Driving habits can also impact the amount of carbon build up. WOT tends to cause the engine to get sufficiently hot so as to burn away some contaminents that would otherwise become deposits. Unfortunately, Ideling around tends to promote the build up of carbon deposits. Having said that, in general, there are two main causes of excessive carbon buildup; burned oil and overly rich air/fuel mixtures.

Oil-based carbon build-up occurs when piston rings become worn and oil is able to leak past the rings from the crankcase. Oil can also leak from valves into the combustion chamber. Typically oil-based deposits appear as dark black and have a gummy, tar-like consistency.

Carbon tends to coat any surface that may be exposed to either the combustion process or handle engine exhaust. It is often most evident on fuel injectors, engine valves and combustion chambers. Deposits also form on the throttle body, spark plugs, intake manifold.

By contrast, fuel-based carbon build-up occurs when an engine burns an excessively rich air/fuel mixture. Too much fuel will tend to produce a relatively large amount of carbon waste that is not as thick as oil deposits but it is hard, dry and tougher to remove.

Causes of fuel-based deposits often include a computer fault, a bad or leaking fuel injector or other potential reasons that cause and excessive amount of fuel to be burned during the combustion process.

In general, carbon deposits can cause a drastic drop in both fuel economy and performance. Because so many performance boats on the water rely on computers and sensors for optimal engine performance, it is easy to see how carbon deposits can play havoc with modern engines. For example, most boats rely on an onboard computer to adjust the air/fuel ratio.

Particularly thick deposits also tends to increase engine compression simply because the carbon deposits take up more space inside the combustion chamber. Abnormally high compression may result in spark knock (detonation), particularly when WOT under load or accelerating. In more extreme conditions, if carbon deposits are thick enough, the top of the piston may actually come into contact with the carbon-coated cylinder head or valves. When this happens, the sound resembles a hammer noise or like a rod bearing has gone bad.

Here are a number of signs to keep an eye out for if you suspect carbon build-up:
-Engine pinging
-Hesitation
-Poor acceleration
-Spark knock
-Lack of power
-Carbon coated spark plug
-Repeated stalling in cold weather
-Engine ping or a hammering sound

Good luck VV