Re: IHC H plug fires only with wire removed...

Posted by Bob M on May 11, 2006 at 04:47:39 from (151.190.254.108):

In Reply to: IHC H plug fires only with wire removed... posted by R. Smith on May 11, 2006 at 02:59:34:

Problem is the plugs are gradually fouling - even if you cannot see the fouling on the plug tip insulator.

What happens is as the tip insulator becomes fouled it becomes partially conductive. Voltage from the distributor then "bleeds" along the insulator to the plug shell rather than appearing as a spark at the gap. However by pulling the plug wire off a bit, voltage must build up sufficiently to bridge the new additional gap, and when it does there's enough energy to cause a spark at both the new gap AND at the plug. So the misfire disappears when you pull the wire off a bit.

Causes can be many - oil burning, plug heat range too cold, excessive idling or running too lightly loaded, carb set too rich, conductive additives in the fuel (lead, mystery oil, etc.) Sometimes a small coolant leak (eg. head gasket) will cause this too.

First thing I'd suggest is replacing the plugs with a set 1 or 2 heat ranges higher and see what happens.

Replies:

• Re: IHC H plug fires only with wire removed... Allan In NE 05:04:45 05/11/06 (0)

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