Oil in the cap can be one source of the problem. The other is more serious. If the bottom portion of the distributor is not seated correctly, one side of your engine is not getting the same oil pressure as the other side!! Since the distributor is going to be out replacing the intake with an Edelbrock Performer or RPM dual plane type will help your engine breath better. Performers start at only $119.00.
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Gerardo
1983 Custom Truck
TX Plates: "BAD BOW"
http://www.geocities.com/abetterchemist/