When I got my heads cam and intake and a few other mod’s, I had a problem kind of like that but mine was for a different reason. I forgot to put the cap back on the distributor and the spark was jumping from the rotor to the cap and it was not aligned right. I cannot belive I am telling every one that; I feel so stupid.
Your problem is probably the distributor being 180 out.
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James Cox
nochevy@hotmail.com
1991 Mustang LX
12.565 @109.38mph 1.764 60ft