Main air bleeds

[Jim Jones]

Cliff and forum.
I am working on a 1971 Buick Q-jet 7041540, and have discovered the main air bleeds to be quite small. 0.040" in the air horn, and 0.038" in the main body. The specs of the car it is going on are: 462 cu. in. 9:1 static compression. Cam is 241 degrees at 0.050" valve lift both I and E,  112 degree lobe seperation.

From GM this carb was equipped with 73 jets and 43 rods.  The carb could have been a remanufactured unit, but the air bleed restrictions seem very small compared to the jet size.  What would be your recommendation for main air bleed restrictions?

Cliff...BTW, I am going to try to visit your parents one day next week. I will try to stop by and say hello.

Regards to all,  JPJones

[Jim Jones]

Sorry...I meant to say the carb was originally equipped with 44B primary rods.

[Cliff Ruggles]

Jim, the airhorn could have been replaced, or the carb commercially remanufactured at some point.  I don't remember any of the 455 carburetors from 71-74 having upper main airbleeds that small.

Stop by anytime you get up this way.....Cliff

[Jim Jones]

OK...Here is the list of mods I made to the carb.

Idle tube restriction,             0.038"
Idle down tube,                    0.055" (no enlargement here, they were already 0.055")
Idle air bleeds ,                     0.070" (upper and lower)
Acc. pump discharge holes,   0.028"
Idle screw restriction,           0.096"
Main air bleeds,                     0.070 (Body and air horn)
Primary jets,                          0.067"
Primary rods,                         None (vacuum hole plugged with check ball and modified piston)
Fuel inlet,                               0.135"
Float level,                             0.3125"
Secondary well restriction,     0.035"
Secondary POE restriction,     0.055"
Secondary tube restriction,    0.036"
Secondary rod hanger,           0.545" (G)
Secondary rods.                     0.410" (CE)

Drove the car yesterday with this carb. Feels very strong and smooth at all RPM even though converter is much too tight. Will idle in gear at 800 RPM  and I still need to fine adjust the mixture screws.  Mechanical advance is not returning fully after a WOT blast, will need to address that next. No way It will get to the track until spring though, TOO BAD!

Cliff, I can't say enough about the information in your book. I will recommend it to everyone.  I never expected this cam to idle at 800. I am amazed.

Best Regards.         Jim.

[Jim Jones]

As it turns out, carb is extremely lean on cold start up. I suspect a 0.070" restriction in the upper idle air bleed is allowing too much air into the idle mixture.  I plan to reduce the restriction, and will post results.

JPJones

[Cliff Ruggles]

Jim, we have custom drive in or screw in airbleeds, and anything else you would need for the carb.

At a minimum, replace the secondary cam/spring, upgrade to the later design accl pump with Viton seal, garter spring, and new pump springs. 

We also have Viton tipped HP fuel inlet seat assembies, and stock all jet numbers from .065-.077". 

Most jets, if you pin gauge them, will NOT be within specs....Cliff