I just got a newer vacuum advance from a freind who had spare parts. So i put it on. I have a 302 and I'm pretty sure the part came off of a big block. I was wondering could the wrong vacuum advance cause my engine to backfire by not advancing it right. The diaframe on the old one is a good bit smaller than the new one. I figured this because it only backfires in gear whenever vacuum changes. So should i go ahead and get the right part or do what?

 

This isn't a linear troubleshooting path. Did the engine backfire prior to installation?

You need to use the correct vacuum advance for the application.

 

Don't think it did.