Plugs and heat range

[llerrad]

Merc. 888, ford 302, ser. # 3689967, 1974-77, autolite dist. new points new cap etc. compression all cyl. 110-115, plugs champion RF10C or AC C83T, per book, removed old plugs soft back coating all round on every plug all the same no build up of crud. This plug seems to be a very cold plug but what is called for, but everytime I change them out they have a black carbon coating not a brown look. could this plug be too cold now we are using unleaded fuel with some ethenol in it?

 

[llerrad]

Re: Plugs and heat range

bump

 

[John_S]

Re: Plugs and heat range

I don't know your motor but black plugs are usually an indication of over rich fuel condition.

 

[EddiePetty]

Re: Plugs and heat range

.....This plug seems to be a very cold plug but what is called for, but everytime I change them out they have a black carbon coating not a brown look. could this plug be too cold ......

Stolen from the NGK Site.....

Causes of Carbon Fouling:
Continuous low speed driving and/or short trips

Spark plug heat range too cold
Air-fuel mixture too rich
Reduced compression and oil usage due to worn piston rings / cylinder walls
Over-retarded ignition timing
Ignition system deterioration
Pre-delivery fouling

Carbon fouling occurs when the spark plug firing end does not reach the self-cleaning temperature of approximately 450?C (842?F). Carbon deposits will begin to burn off from the insulator nose when the self-cleaning temperature is reached. When the heat range is too cold for the engine speed, the firing end temperature will stay below 450?C and carbon deposits will accumulate on the insulator nose. This is called carbon fouling. When enough carbon accumulates, the spark will travel the path of least resistance over the insulator nose to the metal shell instead of jumping across the gap. This usually results in a misfire and further fouling.

If the selected spark plug heat range is too cold, the spark plug may begin to foul when the engine speed is low or when operating in cold conditions with rich air-fuel mixtures. In some cases, the insulator nose can usually be cleaned by operating the engine at higher speeds in order to reach the self-cleaning temperature. If the spark plug has completely fouled, and the engine will not operate correctly, the spark plug may need to be cleaned / replaced and the fouling cause identified.