[455rebel]

Bought cliffs book, used recipe #2.
Car now idles with the air screws adj 3-3.5 turns out(was 5-5.5 turns out).
Starts great,secondary's come in just right, pulls hard and smooth from any
rpm to 5000 redline.
Slight lean when just off idle. 43 primary rods, 73 mains.
Do I need to open the ifrs more or do I need smaller rods?
Plugs look good.

Ps thanks mr cliff for a great how to book, nice pics too.

[77 TRASHCAN]

Yes, Cliff, is 'da man!!!
If some of you don't care for him, there's a Pontiac website that caters to the XE crowd, don't let the door hit you in the buttocks......

[jonmachota78]

If your carb is apt equipped, try raising it up a quarter turn. Check your T-slot exposure/idle air bypass set-up

[Kenth]

What carb-#?

[455rebel]

7043262 came stock on a 73 Bonnie 455 .
Went from 43 to 41 on the rods,cleared it up at off idle cruise.
Still lean at idle when coasting.
Non adj apt, can I raise it a little? How?
Readjusted air screws , 3.5 out seems best.

[77 TRASHCAN]

You can slightly bend the primary rod hangers....Make some sort of measurement to figure out how much you are bending them, in case you want to un-do this mod...

Try to find a 76-up Pontiac Q-Jet, they are more user friendly, there are still to be had. Easy to spot, look for the tiny silver disc centered under the air cleaner gasket, exactly @ the front most part of the gasket...
Carry on Mr Rambler!!!

[Cliff R]

There is also an upper main airbleed adjustment in the airhorn, under the triangular metal cover. This screw will provide some range of adjustment on the primary side with any particular jet/rod combination.

Some 73-74 non Super Duty carbs will also use larger upper MAB's, and a few have smaller ones. The ones with the larger MAB's typically require a little more staggering of the jets/rods than the smaller ones do......Cliff

[Kenth]

Originally Posted by 455rebel

7043262 came stock on a 73 Bonnie 455 .
Went from 43 to 41 on the rods,cleared it up at off idle cruise.
Still lean at idle when coasting.
Non adj apt, can I raise it a little? How?
Readjusted air screws , 3.5 out seems best.

Is it Mfd by Carter or made by Rochester?

The Carter unit has #74 jets and #44 rods with .050" upper MAB´s.
The Rochester unit has #71 jets and #41 rods with .083" upper MAB´s.
The later is obviously somewhat leaner calibrated in this area and will need rejetting OR resizing the upper MAB´s to .070".
Both units has .045" (Carter) - .047" (Rochester) idle channel restrictions and i have found they need to be at least .057" to cure off-idle hesitation.
Also, both has .110" idle bypass air and a .124" choke channel wich requires enlarging the idle tube restrictions (IFR) from .037" (Carter) .038" (Rochester) a couple of thousands.
Going electric choke and plugging the choke channel the idle tubes may be fine as is.

I would NOT bend the primary rod hanger under any circumstances.

Hope this helps some.

[Blued and Painted]

MAB's. . For the un-washed, is that Main metering air bleeds?

[455rebel]

Originally Posted by Cliff R

There is also an upper main airbleed adjustment in the airhorn, under the triangular metal cover. This screw will provide some range of adjustment on the primary side with any particular jet/rod combination.

Some 73-74 non Super Duty carbs will also use larger upper MAB's, and a few have smaller ones. The ones with the larger MAB's typically require a little more staggering of the jets/rods than the smaller ones do......Cliff

I tried adjusting the screw under the triangle,turned it 1/2 turn out,
Turned it out to 2.5-3 turns out,didn't make much difference,seems to be best
Turned all way in, not sure , hardly any change, mabe none.

[455rebel]

Originally Posted by Kenth

Is it Mfd by Carter or made by Rochester?

The Carter unit has #74 jets and #44 rods with .050" upper MAB´s.
The Rochester unit has #71 jets and #41 rods with .083" upper MAB´s.
The later is obviously somewhat leaner calibrated in this area and will need rejetting OR resizing the upper MAB´s to .070".
Both units has .045" (Carter) - .047" (Rochester) idle channel restrictions and i have found they need to be at least .057" to cure off-idle hesitation.
Also, both has .110" idle bypass air and a .124" choke channel wich requires enlarging the idle tube restrictions (IFR) from .037" (Carter) .038" (Rochester) a couple of thousands.
Going electric choke and plugging the choke channel the idle tubes may be fine as is.

I would NOT bend the primary rod hanger under any circumstances.

Hope this helps some.

Carter
It had 73 mains stock, don't remember the rods.
I started with 43 rods(73 - 30 = 43)
Mab now 62(closest bit I had)
Idle channel to 52. /. /. /
Ifr 39.
Already have elect choke,and I pluged the channel.

[Kenth]

Originally Posted by 455rebel

Carter
It had 73 mains stock, don't remember the rods.
I started with 43 rods(73 - 30 = 43)
Mab now 62(closest bit I had)
Idle channel to 52. /. /. /
Ifr 39.
Already have elect choke,and I pluged the channel.

Ok, your main jetting and upper MAB´s are fine, and so are the IFR´s.
I would open the idle channel restrictions some.
As a reference 1973 400 units has .055" ICR´s and 1973 455S.D. has .066".

[Cliff R]

It really helps on the 73 and 74 Pontiac carbs to stagger the jet rod relationship a bit further than 30 numbers. I've built and tuned at least a 1000 of them to date, and we continue to find that they like the metering rods about 32-33 numbers less than the jet size, especially the Super Duty units.

This of course will not hold true for all versions, as you will find three different airhorn upper main bleeds in them, as Kenth pointed out, depending on carb number and manufacturer (Carter or Rochester). There are also other factors at play here, including fuel pressure, float level, size of the inlet seat and float type/weight used. These other factors can seem trivial but they do play a role in final metering to the engine as they all control fuel level in the carburetor.

I also suspect that this new fuel is playing a role here as well, as 10 percent ethanol is pretty standard at the pumps these days, and it has less energy than previous blends, so you engine is typically going to enjoy a little bit more of it to do the same thing...thanks Obama......Cliff

[455rebel]

The screw under the triangle, is it richer(more fuel) cw or ccw?
So the 41 rods sound about right?

[Cliff R]

73/41 would certainly work better than 73/43 in one of those carbs, at least from what I've seen here. You have to be conservative with jet size on the carbs with the extra set of tubes in the airhorn (primary side POE), as it does add some fuel at heavy part throttle.

I tune those slightly different than the ones that didn't use it.

On the 1970 to 1974 Pontiac carbs that screw leads under the upper MAB's. So CCW leans things up some, fully seated CW would be full rich......Cliff

[Kenth]

What Cliff said, though POE is no issue for 1973-74 Pontiac Q-jets as they don´t have it.

[Half-Inch Stud]

Originally Posted by Kenth

What Cliff said, though POE is no issue for 1973-74 Pontiac Q-jets as they don´t have it.

I use the POE tops exclusively on my 455 +060. Just seems right to do.

[Kenth]

Originally Posted by Half-Inch Stud

I use the POE tops exclusively on my 455 +060. Just seems right to do.

Pontiac used two different styles primary POE, one 1969-70 with combined primary pull-over enrichment and secondary well emulsion tubes and 1971-72 style with separate tubes for POE and sec. emulsion.
With proper jetting it´s fine swapping airhorns on 1967-74 Pontiac Q-jets if needed.

[455rebel]

Drove car 20-30 miles yesterday and with the 41s ,it seems not as crisp, in the first
1/3 throttle when on the primary's. Taking top back off today, will be opening the
ICRs up from 52 to 62(closest bit I have).
I'm also putting back in the 43 rods.
Screw under triangle now all way in.
Will post after test drive.

Ps this has been a lot of trial and error dialing this in(yes it is worth it).
Most all of my gear head shop buddies are die hard Holley , I used to be!
Several have commented that they never rode in a q-jet car that operated
Crisp and smooth transition like mine!
Pss they also poke fine at me for having this thing off 20-30 times for adjustments.
Thanks for all the help.

[Cliff R]

Before you pull the top, fine tune with the upper bleed screw. It will lean things out with the current jet/rod combination without changing parts. Make very small adjustments here, and give it some time to evaluate the results. It may take a tank of fuel or even more once you get close, to really know for sure where the best settings are at......Cliff