200 CI auto spark knocking under load- HELP!

[john tate]

So I got the '68 distributor on, thanks to a new O-ring-strange that the NAPA one was too fat.

Been fine tuning some things- car ran well, nice throttle response and no knock...until you get to about 55 MPH and then any acceleration or uphill climb results in constant knocking again.

So I bumped the base timing back from 6 degress BTDC (standard for a '68 distributor) to about 4 degress, but no difference.

Today I disconnected the vac line and plugged it, and no knock at any speed on the way home, but now I have a flat spot on throttle tip in which is expected.

Does the Holley/Motorcraft 1940 just provide too much vac? What can I do to just get a little bit of vacuum but not too much? Can I selectively restrict the line, or what are my options? Would direct manifold vac be a better choice? I think my standard hookup is ported vac, right?

 

[john tate]

forgot that this distributor has an adjustable vac advance, unlike my old dizzy. went out and reset the base to about 5-6 degrees and started backing the alan wrench out to keep it from knocking.

Seems to work, but now it's getting the "flat spot" again at light throttle. Does anyone have the shop manual spec on the vac adjustment for a '68 diz?

Any secrets for getting the vac dialed in just right and keeping the base at 6 degrees or better? It does idle better at a higher base.