7045230 for Pontiac 468?

[Marx3]

Hi, would this carb be a good object for a 468 pontiac (1973 455 ) ?
engine has 7M5 114 cc heads, rpm intake, and a 278/290 adv. dur. Crane cam, M21 and 3.55 gearing.

Upon disassembly i discover that this carb has the 3 brass tubes in the airhorn, plus that extra jet/rod in front of the powerpiston ( I thought I would never see this )

Now I have doubt as to how good this carb would be, even if it is an 800 cfm unit.

If it is good, I am thinking recipe 2, as of now ( 650 Holley ) it pulls 14-15 Hg at 800 rpm.

thanks,  Jacob

[Marx3]

No one knows if this carb is worth rebuilding for bottom-end Pontiac power?

[Cliff Ruggles]

Those carburetors are just as good as any other late model large cfm q-jet.  They are more difficult to set-up, using the early styel APT system and auxiliary Power Piston.  We block off the auxiliary PP and install larger jets and metering rods, the rest of the rebuild, recalibration, etc is the same as any other late model unit, and well described in our book.....Cliff

[Marx3]

Great, so it will get recipe 2.

It has:

jets: 60
rods: 35J

Hanger: N
Rods: DH

Which of these would you change to what, if all bleeds an channels goes according to recipe 2?

[Marx3]

btw, I have your book ( my Qjet-bible! ), and have already built 4 or 5 carbs to recipe 1 and 2, I just need guidelines for the jet/rod-size, and I will be quiet :-)
If I need jets/rods for this rebuild, I will order it from you.

[Cliff Ruggles]

I'd install .073" main jets, and 44L metering rods.  You can fine tune with the APT system if/as needed.

Block off the aux jet, and the vacuum to the aux power piston. 

The rest of the build is the same as any other late model q-jet, except some 75 models still had the upper idle airbleeds in the airhorn instead of in the main casting....Cliff

[Marx3]

Okay, I will place an order for jets and rods!!

I thought upper idle airbleed was prefered in the airhorn?

[Cliff Ruggles]

Doesn't really matter, but you MUST account for the difference in size, as the main body upper bleeds are "indirect".....Cliff

[Marx3]

Okay, got it!

So does the fact that it has primary POE affect the any sizes on the secondary side? and what should be done to the primary tubes?

[Cliff Ruggles]

No, the primary POE does effect the primary side A/F when the throttle is depressed quickly, low vacuum situations, etc.  The jetting I recomended is for the primary POE intact.  If it were not being used, I'd use a 41 or 42 metering rod instead....Cliff

[Marx3]

Okay, I will block off the aux PP. and leave the POE intact.

You mentioned that this carb should have the APT located somewhere in the front area of the mainbody, but I really cant see anything that could be an APT screw etc.

Is it still worth the rebuild, without APT and will the jetting you recommended still apply?

[Cliff Ruggles]

The APT system is the black thing with the single rod hanging out of it that goes into the single jet in the front left (as viewed from the front) corner of the main casting.  It has a brass cup in the airhorn right over the adjustment screw.....Cliff

[Marx3]

this thing?
If yes, what do you normally do to gain acces to it from the outside? Or are you just supposed to take the airhorn off for adjustment?

[Cliff Ruggles]

There is a brass cup plug in the airhorn that can be removed to access it....Cliff

[Marx3]

Are you supposed to leave the hole open, or put back the plug after adjustment?

I guess the tip in procedure is still the same.