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Author
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Topic: drilling holes in butterflies
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V8 Thumper
Gearhead Posts: 4681
From: Phoenix, Arizona
Registered: Dec 2001
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posted 10-12-2002 11:49 PM
   
...for idle quality and/or tune-ability? I've gotta keep in mind... "If it aint broke, don't fix it". My 3310 topped 333 ci Windsor sure dosen't like to idle much below 700 rpm, that dosen't bother me much (four speed  ) I don't have a/c or power brakes to deal with, so the idle chop of the Comp 270S is nothing but  , although it is rough and the mixture screws do nothing to improve manifold vacuum or idle quality. Off-idle response is awesome, no stumble or hesitation at all. Is there anything to be gained by drilling the primary butterflies? Oh yea, almost forgot: RPM Airgap manifold  [This message has been edited by V8 Thumper (edited 10-12-2002).]
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Rustang
Gearhead Posts: 821
From: Clarion PA
Registered: Nov 2000
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posted 10-13-2002 12:43 AM
Before you drill the throttle blades, try opening up your secondaries idle adjustment. There's a small set screw looking screw on the diaphragm side. Open it up a little more, and this should allow you to crank the idle down on the primaries so the transfer slots are closed enough to gain your idle fuel adjustment back.
------------------
'68 mustang 351 clevor- 10.92@124
'67 Stang, 351W -11.18@118
'69 351C Torino-14.90@100
'78 Pickup 351W-15.56@88
'79 Pickup 460 ET=??
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Just Strokin
Gearhead Posts: 754
From: Tuscaloosa, Alabama
Registered: Dec 2001
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posted 10-13-2002 07:08 AM
Maybe this will help also...It is from the Holley website...http://www.holley.com/HiOctn/TechServ/TechInfo/Trblsht.html QUESTION I have a camshaft with a long duration and a high lift. It will burn your eyes at a idle. What can I do to fix this? ANSWER The most common cause is an improperly rated power valve. You will first need to choose the correct power valve for your application. This is covered in another section of the Technical Information Library. When you have a camshaft of this configuration it requires more air and fuel for it to operate efficiently. This in turn requires you to raise your curb idle screw to obtain the same given rpm that you had with a stock camshaft. If you are having a problem with the air/fuel mixture screws not making a difference then what happens is with turning the curb idle screw in farther this will sometimes cause the throttle plates to open too far and they will uncover the idle slots. This will allow it to bypass the idle circuit and start pulling fuel from the transfer slot. To correct this problem you can raise the secondary throttle plates a little with the secondary adjusting screw allowing more airflow into the engine. This will allow you to lower the primary throttle plates so you will be able to get back into the idle circuit. Another method would be to drill a 1/64" - 1/8" hole in each of the primary throttle plates on the side closest to the transfer slot. This will allow extra airflow into the carburetor also alowing you lower the primary throttle plates. ------------------
Larry No fast Fords at this time but one fine cruising 96 F350 CC DRW Power Strokin diesel.
And one rusty 64 Fairlane nick-named the Rust Bucket....And sometimes called the Money Pit...
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V8 Thumper
Gearhead Posts: 4681
From: Phoenix, Arizona
Registered: Dec 2001
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posted 10-14-2002 08:50 PM
Great stuff guys, as always.
Thanks
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gregaust
Journeyman Posts: 27
From: australia
Registered: Jul 2002
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posted 10-15-2002 06:52 AM
If the idle mixture screws do nothing it may be a case that you dont need more air as in drilling the butterflies but you need to reduce the fuel from the idle circuit..There is a mod listed in some holley books that uses .015-.020" fuse wire approx 1/2" long inserted into the idle holes in the metering block . it may take a little experimentation to get it right but you will then be able to get an adjustment on the screws..
Keep in mind this is only a suggestion based on the assumption that you do have a rich idle which is possible with that carb on 333ci .I have had to do this on 351's also..H-T-H
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V8 Thumper
Gearhead Posts: 4681
From: Phoenix, Arizona
Registered: Dec 2001
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posted 10-15-2002 07:06 AM
That's a great tip Greg, thanks Yep, it is a whole lot of carb for (only  ) 333 ci. I had this carb sitting around, so rather than shelling out another $500+ for another one, I figured it was worth a shot, and here's why:
Trick Flow heads, the above mentioned 270S and airgap manifold, 10.06:1 c/r, all MSD, Hooker SuperComps, she definately breathes deep for a little Windsor It's in my '65 GT coupe, and it's my weekend fun car, not a daily driver. I get 8-9 mpg, but oh well
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V8 Thumper
Gearhead Posts: 4681
From: Phoenix, Arizona
Registered: Dec 2001
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posted 10-15-2002 07:10 AM
Hey! Where are my manners?  Welcome to M&M You Aussie guys tend to post about this time during the day... what date/time is it down under at the moment?
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Moneymaker
Administrator Posts: 27499
From: Lyons, IL, USA
Registered: May 99
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posted 10-15-2002 10:51 AM
Welcome to M&M Greg !I would try cracking the secondary a bit Todd. It's a quick and easy test. ------------------
Alex Denysenko
Co-Administrator and Moderator NHRA/IHRA/SRA member and licensed Superstock driver
MCA member# 53321
NHRA and IHRA SS/LA National Record Holder '00, '01, & '02
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Professional Manwhore
The Barry of BarrysGrrl Quote #1: "I never met a magazine mechanic I liked."
Quote #2: "Make sure brain is in gear before engaging mouth!"
Quote #3: "If you can't run with the big dogs, stay on the porch!"
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Just Strokin
Gearhead Posts: 754
From: Tuscaloosa, Alabama
Registered: Dec 2001
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posted 10-15-2002 03:00 PM
The secondary adjustment screw is a bear to get to on many carb/manifold combo's.....you could try inserting a feeler gauge inbetween the arm and the screw. This would let you see if this change will allow the idle mixture screws to have an effect.Once you open the secondaires a little, idle the carb down with the idle screw and see if the idle mixture screws have an effect. You might have to change the thickness on the feel gauge a few times. It is also possible to 'reshape' the bracket on the secondaries where the vacuum diaphram arms attaches to adjust the opening of the secondaries without pulling the carb. But, I would pull the carb once for sure and see how much the secondaries are open.
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gregaust
Journeyman Posts: 27
From: australia
Registered: Jul 2002
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posted 10-18-2002 07:12 AM
Thanks guys...The time here is about 14-15 hours ahead so the time showing on this site is around 7am but its about 9pm at night.
That carb should work nicely on your setup,what i meant was perhaps since the carb is a universal calibration for anything even up to bigblocks that the idle circuits could be a little rich on the smaller engine..
Not that i've tried it but i believe the secondary adjustment screw can be removed and screwed back in from the topside ,hence you can adjust the sec butterflies without having to remove the carb..
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V8 Thumper
Gearhead Posts: 4681
From: Phoenix, Arizona
Registered: Dec 2001
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posted 10-22-2002 07:59 AM
Opening the secondaries a bit didn't help much  70/73 jets, 6.5 pv's, I could go just a touch richer. Has anyone else tried this 'wire' trick in the idle circuit holes? It sounds straightforward enough, just wondering if there's any tricks to it, or anything I should know
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