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1957willyman 05-03-2013 08:54 AM

idle air bleeds
if iam rich at idle and have timing real close how far do i increase idle air bleeds would it help if gave more air at idle by drilling 3/16 hole in primary butterflys

33Willys77 05-03-2013 10:07 AM

Changing air bleeds can make things change real fast. Why drill the butterflies when you have air bleeds that you can change easier than taking the carb off and drilling?

F-BIRD'88 05-03-2013 11:13 AM

What makes you think it is actually "rich" at idle?

it is very very rare that anyone needs to mess with the idle air bleeds.
Very small changes +/-.001" make a big difference.
It is very easy to screw it up.
It is very unlikely that anything needs to be drilled at all.
Put the the friggin' drill down.

post complete engine specs/carb sepcs and tune up specs. It is probabily not rich at all.

F-BIRD'88 05-03-2013 11:25 AM

searching your other posts: You have a comp Thumpr cam.

This cam requires full locked out timing to idle correctly.
Lock out the distributor advance curve. set the locked timing to 38deg BTDC
It does not move with rpm.
Remove the carb and flip it over and reset the pri and sec throttles at idle for proper T slot exposure at idle.
install a new 3.5 or 4.5" rated power valve.
Reinstall ,,, set the (now locked) timing at 38deg BTDC and warm it up. reset the idle mix screws for best idle.
If the plugs are fouled replace.
Be sure the PCV valve is installed and functional. It is part of the idle system on your carb.

BE SURE the starter mounting brace bracket is installed. If yours is missing get one.
If it is hard to re start hot install and use a ignition power interupt switch

When you lock out the timing curve (38deg BTDC LOCKED full time) and get the pri and sec Tslot throttle exposure corrected and the right 3.5 or 4.5" power valve it will idle.
This is the nature of the Thumpr cams. You will need a 10" high stall torque converter. A stock converter will n ot work with
that Thumpr cam.

There is no free lunch when it comes to camshafts... The racey Pro Stock "Thumpr" idle comes at al cost.
If you don't like it replace the cam with one with a wider LSA. Less overlap.

1957willyman 05-03-2013 11:39 AM

sorry f-bird88 kinda new to stuff i know when it is idling in shop it makes my eyes burn real bad i heard that a lean mixture can act like a rich mixture i was asking about plugs cause i dont know what are good plugs or good plugs right now iam running NGK

oldbogie 05-03-2013 12:04 PM


Originally Posted by 1957willyman (Post 1672486)
sorry f-bird88 kinda new to stuff i know when it is idling in shop it makes my eyes burn real bad i heard that a lean mixture can act like a rich mixture i was asking about plugs cause i dont know what are good plugs or good plugs right now iam running NGK

You don't drill the throttle plates unless to get the needed idle RPMs the throttle blades are opened far enough to expose the off idle transfer slot. If that is exposed the idle will be very rich and hard to control. The sole purpose of the drilled hole is to admit enough extra air to allow the primary throttle blades to be set under the idle transfer slot at idle.

There are other ways of getting more idle air into the engine without drilling the butterflies. Most carbs have a stop that ends travel of the secondary butterflies when they are closed. Often this stop is adjustable, usually from beneath with a screw. They can be cracked open just a little without causing secondary fuel metering to start. You can also modify solid stops by drilling and tapping for am adjustment screw, or use a shim attached with some super glue or epoxy.


F-BIRD'88 05-03-2013 12:25 PM

The idle mixture is not "lean" or "rich"... It is late.... More timing at idle corrects it. 38deg BTDC locked out.

the fuel is burning LATE and burning in the exhaust. More timing at idle corrects this. YOu CANNOT smell a rich or a lean fuel mix but you can smell incomplete combustion. That is the stink and eye sting.

The EGR effect exhaust reversion dilution at idle caused by the big cam overlap slows down the fuel burn speed at idle. So the timing requirement at idle is different than what you are used to.
It needs a lot more idle timing. The locked out distributor allows this.
Now the fuel burns quicker at idle. less reburn in the exhausdt t idle. a lot less eye burn.
Take it outside, Fix the distributor and carb. Drilling is not nessessary.
Lock out the mechanical advance system. Set the locked timing at 38deg BTDC. Then connect the vacuum advance to the PORTED vac adv on the carb.

Make sure the PCV is hooked up and working as designed. This give extra air flow at idle.

Spark plugs: Nothing wrog with NGK but because the setup is wrong it will likely foul the plugs.
Fix it. What is the NGK plug number? What cylinder heads? casting number under the valve cover?

it depends on what heads you got.

F-BIRD'88 05-03-2013 12:33 PM

If your starter motor brace bracket is missing get it and install it.
(junk yard, GM parts dealer, the bottom of your tool box) It is required.

F-BIRD'88 05-03-2013 12:37 PM

Spark plug recomendation: What heads?

F-BIRD'88 05-03-2013 12:57 PM

If you already drilled holes in the throttles you will likely need to solder them up or Jbweld them up or replace
with new. ALL ADITIONAL IDLE AIR FLOW adjustment for big cams beyond getting the pri and sec throttles idle position correct, is easily achived thru adjustment of the flow orifice in the PCV valve. Do not eliminate the PCV. It is your friend.
There are different ones with diferent flow specs. If required.

Quick fuel and AED sell carb throttle blades as replacement service parts.
Just be sure to peen lock and or Locktite the throttle blade screws so they cannot come loose.

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