I must second JohnZ's experience with the B28 vacuum advance can. I recently switched from a B1 to a B28, and it pulls between 17 - 19 degrees advance at idle with my 10 - 11" Hg. idle vacuum. I had to limit it to 16 degrees with an adjustable vacuum advance limiter cam. The B28 is rated to yield 8 distributor (16 crank) degrees at 5.75 – 8” Hg, but I am sure they can vary.
L78 Steve...Is it possible that something is hanging up the vacuum plate? Maybe your the B28 is not functioning properly.
Last night I made the following adjustment to my Holley carb and road tested the car today. See my base line listed earlier in this discussion topic.
- Primary side - changed the jets from #68 to #72, and retained the #65 power valve.
Secondary side - retained the #76 jets and replaced the power valve block off plug with a #65 power valve.
Reinstalled the vacuum secondary check ball.
Readjusted the idle mixture screws for a max vacuum between 10 - 11” Hg.
: Great throttle response and a noticeable increase in power thru the RPM range to red line!
Making the modifications (from the stock set-up) to connect the vacuum advance to full manifold vacuum and pull in the vac advance at idle has really made a difference. These modification really help to make the 302 come alive!
The only issue now is after I drive and park the car, I smell a hit of gas so I must be a bit on the rich side. Does anyone else get this smell?
I may try #70 jets on the primary side next.
Attached is a picture showing the simple swap between the A.I.R. hose and vacuum advance hose lines (as JohnZ recommended). The vacuum advance is now connected to a full vacuum signal from the t-fitting at the base of the carb, and the A.I.R. hose is connected to the ported source on the carb. The A.I.R. line was blocked with a ¼” section of a plastic golf tee so it actually now a vacuum plug. The lines are easily swapped if necessary for a car show.
I still need to dial in the centrifugal advance curve and I should be all set.