I rebuilt the carb on my 72 Riv, but it still runs hot and lean when tuned to factory specs. I'm thinking different jets and rods will help out. Does anyone know where I can find out the optimal jet/rod combo for stock 455's with quadrajets?
Hi (name please), If you have the 72 carb for your 455 it is probably the 7042240. That is an 800 CFM carb. The stock jets are .073 with 44B rods and CT secondary rods (.0774 tips very lean). The general rule is when you go up 2-3 primary jet sizes, you go up 1 primary rod size. The 72 Stage1 carb 7042242 has .075 jets with 45B rods and CV secondary rods(.0527 tips-much richer). My John Osborne Q-jet 7042240 has .076 jets and 46B rods with BG secondary rods(.0397 tips). I would try getting some richer secondary rods first. They are easy to change and will richen your WOT mixture quite a bit. On a stock engine, if you want just duplicate the Stage1 jetting. You should still be able to order jets and rods at your GM dealer or speed shop(Edelbrock now makes Q-jet replacement carbs). I also suggest you purchase Doug Roe's book Rochester carburetors(HP books-#014). It's a great source guide for tuning and part specs and part #'s. Hope that helps.
Larry, You say that CV's are rich? They look like dowel rods to me. It definitely helps to get richer secondary rods for that 4 barrel pull. I went from CV to something close to AX, and they are sharp enough to draw blood...almost:grin:
Adam, CV's are stage1 rods, they are not the richest, but not bad. I have seen some really thick ones though that are alot worse. And stop poking your self with those rods:laugh: :laugh:
oops... Just looked at my pile of rods.... CZ is what I was thinking of. Those are the unsharpened pencils that need to be thrown away.
Thanks for the advice. I replaced the secondary rods, and I like the way it accelerates. Now I'm wanting to fine tune the primary jets and rods. I just wondered what size of them is optimal for a daily driver. Seems like it's possible to get the same opening size with lots of different combinations of sizes
I would simply duplicate the Stage1 jetting. That should be more than optimal for a daily driver that is stock. See my first post.
Larry, looks like we have the exact Q-Jet set-up from John. I will be doing some tuning this Sunday at the Fayeteville dragstrip. Three racer friends will be there to help me tune :TU: . Some of them are mad at "Buicks" right now since Tom R. won the last Top Stock race at Norwalk :grin:
I did some tuning today at the track and found out leaning things out helped. My best run was with .053 secondary rods, I did not have anything between .043 and .053. I did try some .055 rods and it slowed a bit, never poped though. I think my ideal secondary metering rod right now is ~.048" (with my current primary rods 46B and .076" primary jets). Unless I turn some secondary rods down it looks like the closest standard is in the medium tip length is a CY or DA (.0443"). I think I'll lean out the primaries a tad, and experiment with the secondaries again next time. It was great to have a 1.91 60' on street tires . I ran a best of 12.70, now were talking :TU:
