[Greg Reid]

I have a '71 Rochester 7041264 Q-Jet. I have it completely torn down including the idle tubes out. Before I put it back together, I'd like some guidelines on improving the idle circuit.
The engine it's going on is a '71 YS with the stock 096 heads...so, it's basically a match for the engine in factory form. As far as I know, the only mods to the engine are headers and a slightly more radical than stock cam...Let's say it's somewhere between an 068~744 cam..
I had this carb on my '68 for about 10 minutes. That engine has about the same cam (Crower 70242). The carb would not idle on that engine without increasing the throttle angle until the primaries were supplying most of the fuel. Also, the mixture screws were all the way out. In other words, useless in it's present form.
I'm just looking for a decent idle for this car. It's a lawn ornament but it runs and moves. It's not driven on the street presently. I just swapped the Torker II and Holley for a stock manifold so I could use this carb.

These are the specs that I wrote down some time ago-

Idle tubes- .029"
Idle down channels- .044"
Upper air bleeds- .044"
Lower air bleeds- .060"
Bypass air- .080"
Mixture screws- .090"

Main Jets are 72. Primary rods are 41.

If any of these look way off, I can re-measure...I can't remember what I was using at the time...

OR...would one of the basic recipes in Cliff's book be suitable? If so, which one?

[Cliff R]

Greg, those cams are considerably different, and would require different idle fuel settings.

.029" idle tubes aren't nearly big enough for either of those cams in a low compression 400 engine right to start with.

I would use larger main jets, and take advantage of the upper main airbleed adjustment for fine tuning. It's a nice feature on those carbs. Not nearly as accurate/effective at APT, but it does allow for some fine control of A/F on the primary side without changing parts.

I would get one of our rebuild kits to get the correct parts in the carb and up to par for modern fuel. None of the aftermarket stuff is going to last in this fuel, even the "blue" pumps seals found in NAPA and other higher end kits.

Once you nail down a specific cam choice, making specific recommendations is no problem. I also can supply the tuning parts, PP spring, jets and metering rods to take the guesswork out of the deal.....Cliff

[Greg Reid]

Cliff, it has one of Jon Hargrove's kits in it already. I rebuilt it some time ago for my other car ('68 GTO) but found a '74 carb I liked better for that application. I have plans for that carb also but I have paint to do before I get to that on that car.

THIS car ('66 GTO) I just want to idle properly for NOW. The main thing is I'm switching over from a Holley/TorkerII to a more factory setup. If I search the archives, I think I can find what cam is in it.

I found the specs for the cam that's in it now-

Brand: Crane Cams
Product Line: Crane PowerMax Cam and Lifter Kits
Part Type: Camshaft and Lifter Kits
Part Number: CRN-863802
Cam Style: Hydraulic flat tappet
Basic Operating RPM Range: 2,200-5,200
Intake Duration at 050 inch Lift: 222
Exhaust Duration at 050 inch Lift: 234
Duration at 050 inch Lift: 222 int./234 exh.
Advertised Intake Duration: 278
Advertised Exhaust Duration: 290
Advertised Duration: 278 int./290 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.498 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.527 in.
Valve Lift with Factory Rocker Arm Ratio: 0.498 int./0.527 exh. lift
Lobe Separation (degrees): 114
Intake Valve Lash: 0.000 in.
Exhaust Valve Lash: 0.000 in.
Grind Number: H-278-2