Throttle blades open to far

[Garrett71monte]

So I just got running my 396 with 11-1 compression with a 240@50 solid flat tappet ground on a 108 centerline.  The problem im having is i can't get my throttle blades closed enough to get off of the primary  circuit  and stay in the idle circuit. My bypass air is drilled out to. 125 on each side.  I have no control of my mixture screws. Wondering if I should be looking at drilling my throttle blades.  Any help could be appreciated

[Frank400]

what is the size of the idle components ? idle tube, down channel restriction, idle air bleeds ?  what is the carb number ?


  what is the timing at idle ?

[Kenth]

BBC Quadrajets of the performance era has .138" idle bypass air from factory, so .125" is somewhat small.
I would start with .138" IBA, then look into the idle tubes and idle channel restrictions sizes.

[Cliff Ruggles]

Before adding any more bypass air remove a small manifold vacuum hose and see if it helps.

More times than not there simply isn't enough idle fuel available to the mixture screws.

Not saying here that you may not need more bypass air, but it will only make things worse if you don't have enough idle fuel right to start with.

More specifics would also help:

What is the carburetor part number and exactly what has been done to it?

The details from the cam card would also help.

A 240 @ .050" flat solid cam really isn't that big, but if it's ground on a 108 LSA it will have enough overlap that idle quality will be degraded considerably in a the 396 engine........Cliff

[77cruiser]

I ran a similar 240/108 solid cam in a 385 SBC. It had around 10" vac. I think the IAB was about .140.
Make sure the IAB is open from top to bottom & not blocked by a wrong gasket.
Idle tubes were .039, down channel .055 & mixture holes were .093.

[Garrett71monte]

Thanks for the quick replays. So here are the number.
Carb number is 17056202
Air horn air bleads. 042
Main body air bleads .042
Idle tubes .038
Idle down channel .052
Primary jets 77
Primary metering rods 46k
Idel air bleads main body .070
Idle lower air bleads .063
Idle bypass air .125
Mixture screw holes .99
Da secondary rods
O hanger.
As of now it has way to much fule it seams like because when I screw in the idle screws all the way in it seams to run better. Then I noticed when I removed the carb to look in to my problem is when I saw the transfer alot is exposed. Hopefully the info i posted will help you guys help me. Thanks again for everything.

[Garrett71monte]

Sorry I missed the timing question. My full mechanical advance is at 38 so the puts my initial timing at 18 . I have full vaccum advance with and adjustable vaccum canister set to about 5in of vaccum. I belive at idle it has about 30

[Cliff Ruggles]

Are you listing the MAIN airbleeds at .042" airhorn and in the main casting?

Why all that timing at idle speed?

It should be fine with 18 degrees initial timing provided the compression is 11 to 1.

[77cruiser]

How much vac. at idle?

[Garrett71monte]

Sorry I forgot to include I talked to cliff a while ago about my carb set up going on this motor. Before it had big man air bleads at .114 in the air horn and .118 in the main body. So you sent me brass bushing that I stuffed in to resize the primary air bleads. I have 11 in of vaccum at 900rpm. I'm running manifold vaccum so I can have a stronger idle . I have a 2004r behind it and the torque converter isn't loose enough for when the car is put in to gear. Also im able to lower I'm throttle blades more with the vaccum hooked up to pull in more timing. Or if I'm wronge please let me know. The motor dose not slow crank on start up or dose it diesel when shutting it off at temp.

[77cruiser]

If you make the air bleeds smaller the circuit is going to activate sooner.
I like more timing at idle it's dictated by cam timing.

[Garrett71monte]

So I went up on my bypass air to .141 on each side and it seemed to help out the problem. I seem to have a little control of my idle adjustment screws.  wondering how big I can make the factory holes with out screwing something up. Then back to the timing it just seems that this motor and my last motor  just worked better with full vaccum timing. My next problem is trying to find someone in Alaska that can weld stainless so I can install my o2 sensor.