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took out my plugs 3 are dry and carbon black. 3 are dry without carbon. Whats up with that?
Last edited by wisebri; 08/07/13 12:38 AM.
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Wisebri
Basically I would suggest that the black plugs are not burning the fuel correctly (possibley excess fuel), check the inlet for vacuum leaks especially close to those cylinders without the carbon. It may also be that the plugs are not sparking correctly therefore not igniting the fuel fully.
The worst case check compressions.
Tony
1938 1/2 ton Hope to drive it before I retire
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where in the world is a vacuum at each cylinder?
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The intake manifold runs under a vacuum when the engine is running. If there is a leak in the manifold or gasket between it and the head it will cause the nearby cylinders to run leaner. If the three plugs with carbon on them are 2, 3 & 4 it may be a factor of near normal operation. The front cylinders run cooler than 5 & 6 coupled with the shorter distance from the carburetor to the cylinders results in the center cylinders running richer than the ends.
Now if you have a compression difference or vacuum leak it can dramatically change the normal fueling/combustion pattern.
How Sweet the roar of a Chevy four!
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not sure of the firing order. From front of engine it is 2-5-6 that are carbonless.
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Shade Tree Mechanic
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Shade Tree Mechanic
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As a professional mechanic for 60 years,when I would see a spark plug that was black and carboned up it usually indicated it was probably running too rich. Poor ignition would usually show up as a 'wet' plug from not firing. Start with a compression test, all should be about 100 psi, with no more than a 10% variation between the highest and lowest. If a cyl is low, put a couple drops oil into cyl and retest. If that raises compression you have a leaky piston or worn rings. Little or no change indicates burnt valves.
flip
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thank you for the info. I will get a compression tester and try that. It keeps me out of the refrigerator...
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Backyard Mechanic
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If the "flap" located in the exhaust manifold just below the carburetor is seized in the "closed" position (horizontal) it can pre-heat fuel and cause problems in combustion....JIM
Last edited by james_h; 08/13/13 08:13 PM. Reason: typo
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I have a Tom Langdon split manifold. Fuel is heated with radiator water instead of exhaust flap. Thanks
Last edited by wisebri; 08/15/13 03:36 AM.
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