Dist. Advance Re-curve

[Wbulk]

I just wanted to do an update on this vacuum advance issue because I believe it’s important to cover all the issues. Jeremy and I talked this week and he was having a hard time finding an adjustable vacuum advance for his FE. I had not bought one for a few years so I did some checking. Crane or Accel don’t seem to make them anymore, but I remember reading that some after market companies were making the adjustable ones as standard, so I did some checking with a few auto parts stores. I found some Wells brand vacuum advance units come standard as adjustable. In checking part numbers I found a Wells brand unit FV945 for $21.00 that fits most Fords from 1959 to 1971, but it was not available locally. I called Wells tech people and they pulled one off the shelf. Sure enough it is adjustable.

I also found some mid seventies ones that were adjustable from AutoZone. I took my 3/32 Allen wrench with me to check and none of the parts guys had a clue that some were adjustable, and there was no instructions in the boxes. I checked the adjustment on one of them by inserting the Allen wrench in the end of the vacuum fitting. I found it was adjusted for full advance. I feel sorry for the guy that buys one and can’t figure out why his engine is now pinging and with a simple turn of a wrench it could be fixed.

So why is it important to have an adjustable vacuum advance on a street engine in a Cobra? When you change the centrifugal advance to make it come in sooner like we did, and you have a standard vacuum advance that could add another 20 crank degrees or more, the combination of the two at cruise or slight load can advance the engine too much and create some pinging. Remember we put in lighter springs so the advance comes in sooner. The combination of the two at lower rpms can be too much. To fix this you turn the vacuum advance down with an adjustable unit. Since it is hard to hear pinging with loud exhaust it would seem that 10-15 crank degrees may be in the ballpark, but each engine is different.

You can check and see what you have by checking your timing at idle with the vacuum advance disconnected, and then connecting the vacuum advance to full manifold vacuum and then seeing what your timing is. The difference is your vacuum advance. You may have to lower your idle at full vacuum advance to keep centrifugal from coming in and confusing the issue. In Jeremy’s case the stock vacuum advance was just putting out way too much advance. Hope this helps.

Wayne