Something I built actually WORKS

[curtis73]

I would absolutely love to hear. I have heard so much contradictory information about ignitions in my life that anything at this point would be gold.

I understand vacuum, ignition curve requirements, and how they relate to engines, but how to actually set an engine up for proper operation... I am clueless.

Here's what I know. I want to get about 36* total advance. The mechanical advance in the Mallory distributor provides 22*, so (mechanically speaking) I need about 14 initial. I had planned this based on the fact that the Mallory was set up for ported vacuum; adding advance during part throttle and during throttle tip-in. That all makes sense to me.

I have come to trust your advice, so anything you can advise would be appreciated.

[AllGo'n'Show]

Sweet project man, hopefully my gf is as supportive as your wife

[curtis73]

Originally Posted by benchtest

If you're using a stock vac. advance you may run into knock due to early pull-in, but if you use an aftermarket replacement (at least the major brands such as Echlin, in my experience) you can adjust the starting pull-in point easily. The only requirement is that it have a straight nipple. I'll describe if you're unfamiliar/interested.

Oh, I see what you're talking about now... the adjustable canister that you use an allen wrench to adjust. Yes, this has one. I'm pretty sure this one you turn in to delay advance.

So you're saying that with that adjustable canister I can use it to more closely approximate a ported vacuum curve?

[benchtest]

Pretty much. Actually, just set it so that it takes 4" or more to start pulling in. Should work fine and increase your idle vacuum and idle quality.

[curtis73]

I found today (upon removing the TB that there is in fact no ported source on this carb. It would be easy to add one with an .059" drill. Judging by what you've said, you feel that a manifold source is better. Is that the case?

I agree that the extra advance at idle will help my idle quality, the advance is full at idle and drops off as load increases... which makes sense. The more load you have, the less advance you should have.

After the ported orifice is uncovered, does manifold vacuum = ported vacuum? If that's the case then I understand completely. The only difference would be idle advance which will be better with manifold vacuum. At all other throttle points the curve would be identical regardless of which signal you use... Am I on the right track?

I may still add a ported source for my charcoal canister purge. If I do add a ported source, in your opinion do you think I should keep the ign advance on manifold? Or since I'm going to the trouble of adding the ported source, should I switch?

[benchtest]

If you add ported vacuum, you can use either for the advance. Once the ported hole is fully uncovered it will be nearly equal. There may be a slight difference, but the advance won't notice it. I really don't have a preference, except to say that manifold vacuum on an engine with a larger than stock cam can make a more tolerable idle, and makes a more stable idle. You've got the right idea of it all.

[curtis73]

Excellent... Thank you. You are very good at explaining in words that I understand.