7044223 1974 Monte Carlo 454

[Frank400]

A friend of mine bought an all original 34k miles unmolested '74 Monte with the factory 454 engine. 

   He's installing a larger cam and higher compression heads, along with a few other mods.  His intentions are to install a Holley Sniper and I did not try to sell him the idea to keep his Qjet, he's installed quite a few Snipers in the past and likes them.

   BUT ! ......  he plans to start the engine on an engine test bench and break in the cam before installing it in the car.  He wants to start it with the Qjet and asked me if I would richen up the idle system a bit to make sure he has no trouble while starting the engine.

   So I tear into what seems to be a Qjet that was never opened, and start measuring everything related to the idle system.  I am surprised by a few numbers, among them the idle air bypass size. 

  What do you guys think of this ? Never seen that large of an idle air bypass.

Idle screw discharge hole: .074"
Idle tubes: .038
Idle down channel restrictions: .047
Idle upper air bleed: .068
Idle air bypass: .171

  On another note, the main jet is 74 and primary rods are 40B, main air bleeds are .119, carb date is 0164, the car has no A/C from the factory and has an idle stop solenoid which I guess is for anti-dieseling purposes.

    Don't know if this matters or not, this is a Canadian car.

[77cruiser]

That's big, I've used .141 before.

[Frank400]

yes indeed, that IS BIG !  I never saw the car running but he bought it this past summer and told me it acted like any factory original car of the era, idling around 700 rpm or so.

    The car has an EGR valve, and is (was) most likely very functional, don't know if that has any effect, always been under the impression egr is not active at idle anyway.

[Kenth]

The 1974 Corvette 454 Qjet #7044221 and 1974 Truck 454 Qjet #7044227 also have .170" idle air bypass.

I would start with .040" idle tubes, .052" down channels, .095 idle needle holes, .078" main jets, #48B primary rods and AX secondary rods for what you are doing.

Also cut air valve stop for 35 mm opening measured from back of opened air valves to back of chokeblade housing for full 750 cfm flow. 7/8 turns on airvalve preload spring.

After this he may stay with the Qjet and save money for a better exhaust or new tires :-)

HTH

[Frank400]

Hey thanks Kenth, glad to have your confirmation that it is indeed the original bypass size.  I wonder how it got away with idling at 700 rpm....maybe the timing was very close to zero ?

     I'm reading your posts all the time....where did you acquire all that Qjet knowledge ?

[77cruiser]

What was the initial timing on those? I suspect quite retarded & they need that much bypass.

[Frank400]

Jim, that is the only thing I can think of...

[73ss]

That bypass is big. I have a un-molested 7043200, from a '73 454, LS4 and the bypass measures .137, which is the biggest I have seen.

Looking at the baseplate, I don't see how it could go bigger without breaking through the bottom of the baseplate, the way they are drilled at an angle. Initial timing was 12 on a 73 passenger car with 454. My car still has the emissions decal.