HEI Compression Test Question

[TJUCLA98]

Hi guys, I am new to the forum so pardon me if this question has been answered but I combed through as many searches as I could and didn't seem to find the answer / question.

Here's the situation, I have a 68' step / short with a 250 I6 in it. It has been running very rough. At first I thought it was a spark issue and I wanted to do away with the points dizzy anyway so I swapped out to an HEI. That swap seemed to give the engine a bit of a pep but I still couldn't get it timed just right - seemed to nearly stall at take off and ran rough. The next thing I did was get it up to temp and tried unplugging each spark plug wire one at a time to see if there was a noticeable difference in idle. Low and behold, the #5 plug seems to be the issue, no drop in idle when unplugged.

I am going to take it a step further and give the engine a compression test before scrapping the I6 and going to a 350 all together. The question I have is what do I need to unplug on the HEI dizzy before doing so? Is the Batt wire on the dizzy enough? Any other concerns I should be aware of with a carburetor on the truck?

Thanks a ton for your input!