idle tubes & air bleeds - 2

[Jase_thirdgen]

Let's try this again...

I am curious to know more info on when you recommend putting in or drilling bigger idle tubes and air bleeds. And would I be in need of bigger idle tubes or air bleeds for my application?
If anyone has comments or recomendations on my choices of parts, feel free to comment.

*This setup is going in a 1983 camaro z28 with a 200-4r trans

Carburetor-info: Stock Q-jet
Originally came with a chevy 305cui
Carburetor-number: Casting # 17083280 - 1013 - FSK

Motor-specs: 355cui truck engine (bored 030 over)
~400hp and 415lb/ft at crank 
New +7cc flat top pistons
Stock crank
Fully rebuilt
10.5:1

Rear End Ratio: Rebuilt 7.5in. 10 bolt with 3.42 gear ratio

Heads: Trick flow DHC 175cc intake (TFS-30210006)
74cc exhaust
60cc chamber

Exhaust: Hooker Short headers
Flowmaster 50 series
Dual exhaust 2-1/2 inches diameter

Intake: Edelbrock performer air gap (EDL-2601)

Cam Specs: Compcams 262h camshaft (12-238-2)
1300-5600 rpm range
218/224 duration at 050 lift
262/270 adverised duration
.462int/.469exh valve lift
110 lsd

Thanks for the help!

[Cliff Ruggles]

When you are trying to use a stock emission calibrated carburetor on a non-stock engine in most cases you will need to make some modifications to the idle system.

There are a few exceptions to this as some later model HD truck and Motorhome Q-jets originally used on big block engines have pretty generous idle fuel calibrations. 

Most of the others will not and need a little help.

The camshaft you chose is pretty small for seat timing and a little smaller than a stock 350/300hp cam.  However it is ground on a 110LSA (cam companies do this for "bling" or to produce some "attitude" at idle speed more than anything else), so it may need just a bit more idle fuel and bypass air for what you are doing.

Take a look at the chapter in my book that covers idle system modifications. Identify the different items mentioned, idle air bleeds, idle tubes, DCR's, and bypass air.  Measure what you have and look at what is recommended for similar set-ups.

Part of the rebuild will also require high performance parts vs standard over the counter components.  This includes a high flow N/S assembly and accl pump.

You may also need to increase jet size and smaller secondary metering rods, we have those as well.

Many later model carbs will also have very small holes under the mixture screws and covers over them, plus the screws have "goofy" heads on them requiring special tools to adjust.  We have (just got them recently) excellent replacement idle mixture screws for the 1979-up carbs that have long slotted drive heads for easy access and no special tools required to adjust them.  The are $8 per pair and come in all of our HP rebuild kits.

As far as opening up the holes under the mixture screws on the later carbs we recommend drill them no larger than .090" or you may not be able to seat the mixture screws without tapping the threads deeper, which requires a special metric tap.

I'll add here that we specialize in supplying complete rebuild kits with high performance parts and tuning parts.  We assembly the kits based on the carburetor part number and engine specs and outfit them with jets, metering rods, secondary metering rods, power piston spring and idle tubes.  This takes the guesswork out of the equation so pretty much plug and play.......Cliff

[Jase_thirdgen]

Thanks for the great info! That