1972 Demon 340 engine mods

Miszny said

How does the carb know to use power valve or not? Is it regulated by vacuum or anything more than that?

I seriously doubt that whoever installed this cam bothered with degreeing it.

I will do all adjustments from scratch. Totally gave up on the vacuum secondary carb also because it has multiple vacuum leaks and needs total rebuild.

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The carb doesn't know what power valve to use. You, as the tuner need to check the vacuum at cruise and then pick the power valve accordingly. Let's say you have 12 inches of vacuum at your cruise RPM (since your idle vacuum is so low I'm just guessing 12 inches) I'd pick an 8.5 or maybe even a 10.5 PV. Then you can trim down the T slots a touch more. You just have to keep working with it.