467-Ratman

I am going to run my Holley 780 for the rest of the summer, I have 74 jets in the primary and 80 in the secondary. Its a vacuum style secondary carb. Question is can I or should I go bigger with the jets? Its running ok now, but would like some more grunt. What are some of your combos?

clem zahrobsky

post the LIST# that is on the front of the choke housing as different carb# have different jetting. remember that carbs are jetted for sea level and you can lean them down 2% in area for every 1500' above sea level :chevy

467-Ratman

The list number is 4800, thanks

Matt Gruber

see my tips in sig. for A/F tuning.
Odds are at least one jet is too rich.

clem zahrobsky

list#4800 is a 1970 Z-28 carb pri jet 70, sec jet 76, powervalve #85 :chevy

467-Ratman

Matt, I have not been able to tell on the secondary jets if they are too rich, too busy looking down the road!! The primary jets seem to be ok with my 467 motor, I have checked the plugs after a 20 mile highway cruze and they are a deep brown color, is that ok or should they be lighter in color?

467-Ratman

Clem, I am guessing that the jet sizes are for the original 350 v-8 ? If so they would be or should be larger for my 467 motor? Thanks

clem zahrobsky

dark brown is too rich,the plugs should just be a cigarette ash grey or compare to a brand new plug for just some color. engine size has very liitle to do with the jetting because the air flow is limited by carb size. my 1970 454 chevelle with the same CFM carb used the same jets. :chevy

Matt Gruber

467-ratman
with your power it is hard to drive and read the A/F gauge :yesnod:
David Vizard, in his book, uses a camera to record the run, then plays it back with no fear of :smash:

467-Ratman

Thanks for the help, I will try a set of 70 jets this weekend and see how she runs!

Robert N

For comparisons - My 1970 Holley is running 77 primary and 83 secondaries!! They will be rejetted to 70 and 76. The car is way to rich. Not that Chevron is complaining!!