Tuning suggestions for a 7044276 carb

[Shark Racer]

I'm helping a friend tune the QJet in his 68 Firebird.

The engine is a 400 with a mild cam (don't have specs, would guess duration in the 210s and LSA 110-112). Otherwise, the engine is mostly stock.


He bought the carb on ebay: http://www.ebay.com/itm/rochester-4bbl-quadrajet-7044276-1974-pontiac-400-455-date-1294-/170983509085?nma=true&si=9SQ%252BgAuBEzKXSzHwbqzQDEaS%252BBE%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

So, the info I have is this:
carb #: 7044276
Primary: 73 (looks original) jet, 48C rods
Secondary: DB
Secondary Hanger was C, IIRC

Float height: looks a little low, forgot to bring my mic with me. Should go 1/4"?

Main Air bleeds looked a little bigger than 0.070. No bushing in upper, nearly hogged out bushing in lower.

Idle air bleeds (from eyeballing) looked ~0.070 in lower, much smaller upper. Maybe in the 40s? Idle air bleed was in the air horn, behind the upper main bleed.

Is this calibration correct for the carb?

Any recommendations to start with this one? I have a good collection of jets, but no early rods. A 73/48 combo sounds like a very lean cruise to me, but what do I know?

I was also thinking the DB rods might be a bit lean. I have a huge quantity of CH but nothing else I'd be willing to spare.

[omaha]

Id be worried about the hogged out lower air bleeds but that would be about it. Maybe a slightly fatter jet. Would be nice if you could get the apt adjuster to work. ((hard to do in those older carbs). I wouldn't worry too much about the secondary rods for now as they can be changed without taking the carb apart (very carefully of course). ...Hey aren't those 48C rods the "triple taper" rods. Did not know they used them in Pontiac carbs. Id get the main airbleeds right in line with the recipe one in the book.  Nothing looks too out of line though.

[Shark Racer]

I've heard that the 48Cs are. I didn't eyeball them much when I had the carb apart.

I'm not a machinist so my visual estimates are rough at best. I'm a software engineer.

[Cliff Ruggles]

Way too lean on the primary side.  I would install one of our kits, new jets, and metering rods.  Those carburetors used larger upper main airbleeds, and require a different calibration than other Pontiac carburetors used in that era.....Cliff

[Shark Racer]

Thanks Cliff, I'll give you a call tomorrow shortly after I get up.

[Shark Racer]

Thanks all for the help.

I've put a couple hours into this carb now; installed new upper main air bleeds and sized the lower. Looks like 070 lower, and I sized to 070 upper. I know we should have shot for 067 lower but it's hard to shrink a hole and probably not worth the effort to drive a new bleed in there? The upper was at 081 before.

I've found a few problems with the carb, some of which would likely explain the issues he was seeing:
1. Secondary air valve door, passenger side was binding.
2. Secondary air valve tension was very low at 1/2 turn
3. Crack in primary throttle plate near linkage (will rebush)
4. Float level low (~1/2")

I still need to bush the throttle shafts and stake the air valve screws. We're planning on getting the car back on the road on Sunday. Should be fun! I expect it to run a lot better.

Here's the car it's going into (gunmetal bird):

[Cliff Ruggles]

Nice ride!

You are finding out why we hate to see commercially "remanufactured" carbs come into the shop.  They ALWAYS require more work to get them up to par than original "virgin" units.

Still should be able to get a good end result.....Cliff

[Shark Racer]

Gui is quite happy with the carburetor. This is the "fourth" carb he had on the car.

He started with a Holley, then switched to this. This had the bogging trouble so he switched to an Edelbrock 1407, which he was happy with.

We got the carb on this morning and took it for a drive. The first thing I noticed was the prodigious torque of the 400 - and it didn't feel bad at all at high RPM either! There was a slight hesitation going into the secondaries, which may be because he unhooked the pull-off and forgot to put it back on. Whoops.

Regardless of our little "gotchas", he was absolutely THRILLED with the carb. Said it was "night and day" vs the Edelbrock.

Thanks much for the recommendations and the parts, Cliff.

[Ethan1]

 Nice ride is right!

[omaha]

 Sweeet.....looking ride!  I always like the early firebirds (more than the Camaro's).

[hunter55]

Shark, that is a very nice looking firebird.  If it's a 68 someone has but 67 doors on it because the vent windows were gone on the 68 models.  Love the color.

[Shark Racer]

I was wrong - it's a 67. His other firebird is a 68 'vert. I'm a Corvette guy, myself...

BTW - anyone familiar with the throttle linkage on these things? The metal rod seems to want to re-angle itself as he drives and put itself into a bind. I was thinking going with an aftermarket cable setup would probably be best.