I have been trying to track down the reason for a misfire on one cylinder and did a test with an extra spark plug and ignition wire. I attached a spare plug to the intake manifold and pulled the #7 plug wire off the cap and wired the extra plug to it. With the engine idling, the spark looks very weak, like the spark you get on a weedwacker or chainsaw. I had been expecting a good fat spark, but was disappointed. The HEI has been inspected and has new cap, rotor , and wires. Is there a test that reveal if the spark is too weak?

What's this on/in ?

This might help.
http://www.chevelles.com/techref/ftecref5.html

Thanks, Dean! I have not looked at that techref article in some time. I think it has been expanded and updated with a lot of good info. Will have to look for one of those spark tester tools.

If the problem is a weak HEI spark I have a solution that may work although this is an older post.

stock HEI distributors are notorious for weak sparks.
Do you have a CDI box firing your coil like an MSD? If you dont the easiest or cheaper option would be to install a HEI Distributor (http://www.heidistributor.net) ignition boost system.

You have to use non resistor plugs for it to work. My friend has a dragster and has this installed it, so just thought I would contribute my two cents.