When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Try dropping your timing back some, ~6 degrees is best. It sounds to me like you have valves sticking open, or weak valve springs.
Evan MacDonald
82 F100 FlareSide
84 300-6, 66 240 head
83 NP435(6.69 low)
Blue
Yes your problem is valve/timing related, whether it be a burnt valve, a bad cam lobe, or a timing chain that has jumped. In the worst case, you may have a hole in the top of a piston as well.
Phillip