4 barrel jetting?

[88bluestar]

Current jetting is 72 primary, 80 secondary. Timing is 34-36 degrees roughly, plugs are white. More humidity lately and temp has changed, hotter by about 15 degrees.
Should I jet up on both primary, as well as secondary. Also have a slight hesitation right off idle. Sean Murphy Induction 750 holley.

[Geoff2]

Need waaaaaaaay more info on the combo....

[econo racer]

More info needed. If you have a powervalve in front you might try 2 sizes larger Presumming no PV in rear I would leave it alone Need way more info and will try to help.

[mag2555]

What cid motor are we taking about here?
That 72 primary sounds lean to me, or at least the primary to secondary spread sounds too big!
Is the Carb a model with 4 idle circuits?
Open header?

[88bluestar]

355, 9.5:1 pump gas(91)
Bowtie Vortec large runner head, 215-225cc(was bought this way so unsure of if its a early 371c head or later after they made runner changes.
raised runner chevy bowtie intake, plan to sell both heads and intake after race season however, Im aware they are wrong for the combo.
3000-7000 rpm range custom 4/7 comp cam 252/255 108L advanced 4 degrees. just 1 3/4" headers 3.5 collector
3.48 stroke
6.125 rod, unsure of what piston it has.
,

[Frankshaft]

Current jetting is 72 primary, 80 secondary. Timing is 34-36 degrees roughly, plugs are white. More humidity lately and temp has changed, hotter by about 15 degrees.
Should I jet up on both primary, as well as secondary. Also have a slight hesitation right off idle. Sean Murphy Induction 750 holley.

I would jet up equally​ on both front and back. Start with 2 sizes. To keep balance. It will tell you if it likes it. The slight stumble could be from needing more jet too. If plugs are white, it likely needs more fuel.

[tresi]

Don't be fooled by unleaded pump gas. Plug porcelain nose should look they came out of the box for street use. Any color if any should be deep in the shell. They can be light gray for drag racing. Cure your off idle stumble with the pump cams and squirters.

[user-17438]

Don't be fooled by unleaded pump gas. Plug porcelain nose should look they came out of the box for street use. Any color if any should be deep in the shell. They can be light gray for drag racing. Cure your off idle stumble with the pump cams and squirters.

This. Also verify base timing is enough.

[88bluestar]

Vacuum leak possible?

[cjperformance]

1st up is your fuel supply system able to deliver what your engine will need? Fuel flow test thru N&S's?

[MadBill]

Current jetting is 72 primary, 80 secondary. Timing is 34-36 degrees roughly, plugs are white. More humidity lately and temp has changed, hotter by about 15 degrees.
Should I jet up on both primary, as well as secondary. Also have a slight hesitation right off idle. Sean Murphy Induction 750 holley.

Especially with a carb of unknown history, I like to disconnect the secondaries, optimize the tune on the primaries then reconnect and fine-tune with only the secondary jets. I've seen as much as a 15 HP gain with no change in AFR by going richer on one end and leaner on the other.

[1972ho]

http://www.quickfueltechnology.com.au/c ... s-AUST.pdf Check out the what some of QF standard jetting are.