[steve25]

The problem with a motor of a given CID that is running a Cam with over 78 degrees over overlap and close to not enough compression on the street is that like Cliff posted tuning it to run well below 2200 rpm or so takes experience.

Many street motors that are cam'ed up to being on the edge of not having enough compression will produce more vacuum at just off idle then at idle .

Couple this with the fact that the lower your compression is and the leaner you try to go the more timing you will need.

Even if you have enough compression to work well with your Cam you can not escape the basic fact that at idle with clean burning idle mixture any motor will need more lead timing.

Motors like this need more initial timing and then less mechanical timing that like Cliff points out then needs to come in slower.

The dyno / builder guys who just lob off the vacuum advance and stuff the lightest springs into the Dizzy are doing themselves a time saving deal, but short changing the owner of the motor.

Situations like this are where computer programmable timing set ups are more helpful then having fuel injection.

If you have a motor such as this you need a vacuum gauge and your timing light to work things out.