acceleration issue

cincydelta

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Thread starter
Oct 12, 2023
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Hello All,
I have a problem with my 1966 Delta 88 convertible that I cannot seem to figure out and was hoping for some/any input so I can get it back on the road.
The 2 issues I have are first when I accelerate past 20 mph the car starts shuddering and I'm concerned that I will damage the engine, so I quickly return to my garage.
The second is that the trans leaks but that is secondary as I think its a pan gasket but haven't gotten under the car due to the first issue.
I have a 425ci with a Holley Speed daemon intake and 750 cfi carb. The car starts and idles fine. What I have done so far:
1) set the timing for 10 degrees was at 7 but i thought it idled better with more advance.
2) I checked for and found no vacuum leaks around intake manifold and carb but still replaced carb gasket and tightened manifold bolts to 30ftlbs.
3) adjusted the carb screws with a vacuum gauge and got a decent steady reading of 19 it fell to 15 when shifted into drive under load.
4) I ran a compression test with the car 1st cold then warm and except for cylinders #6 & 8 all the readings were 140 to 150 (cold) with 125 n 130 for the other 2
after warm up the readings were between 135 and 145 except 6 n 8 at 125 n 130 again.
I don't see any antifreeze missing and the car isn't overheating, should I be thinking head gasket issue?
Please advise I'm at a stand still here.

Regards,
Joe