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  #1  
Old Jun 23rd, 08, 8:03 AM
creeper72 creeper72 is offline
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Default 4 corner idle adjustment

Could some of you please open some discussion on the best way to do this. I have heard so many different methods. I would like to find the best way and learn & stick with it.Search didnt turn up much. Examples of conflicting methods. I know it may be boring to some, but it could help some out.

Secondaries same as primary ?
All 4 equal ?
adjust 1 at a time or all 4 ?
Highest Idle + 1/8 turn rich/ highest vaccum/dont use vac at all ?

My latest carb is a Holley 950 HP, has holes drilled in throttle plates, motor is a 468 with rough idle about 10 " Vac.
You get the picture by now.Thanks for any help.
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  #2  
Old Jun 23rd, 08, 8:18 AM
creeper72 creeper72 is offline
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Default Re: 4 corner idle adjustment

Here are 2 ways I have used, I used method 2 on Friday.As you turn only 1 screw it is easy to feel the change, but then turning the other 3 to match seems like a big change each time ????

Metod 1
turn the rear idle screws in to stop, then out about 1/8 turn. turn the front in to stop, then out about 1.5 turns. start it up, let it warm up good, adjust the fronts to lean best (highest vacuum) plus 1/8 turn out, you should be real close.



Method 2
with the car warm at idle and the screws 1 1/2 turns out turn all 4 or 2 if the rear doesnt have mix. screws in a 1/4 turn . if it idles faster go another 1/4 if it slows go out until you find the highest idle. reset your idle and check again.
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  #3  
Old Jun 23rd, 08, 9:13 PM
creeper72 creeper72 is offline
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Default Re: 4 corner idle adjustment

Ttt
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  #4  
Old Jun 24th, 08, 1:19 AM
Camaro_fever68 Camaro_fever68 is offline
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Default Re: 4 corner idle adjustment

Quote:
Originally Posted by creeper72 View Post
Could some of you please open some discussion on the best way to do this. I have heard so many different methods. I would like to find the best way and learn & stick with it.Search didnt turn up much. Examples of conflicting methods. I know it may be boring to some, but it could help some out.

Secondaries same as primary ?
All 4 equal ?
adjust 1 at a time or all 4 ?
Highest Idle + 1/8 turn rich/ highest vaccum/dont use vac at all ?

My latest carb is a Holley 950 HP, has holes drilled in throttle plates, motor is a 468 with rough idle about 10 " Vac.
You get the picture by now.Thanks for any help.

It depends on idle rpm, engine characteristics, and the carburetor's calibration. With a lot of the "out the box" Holley and Holley type carbs, it's almost impossible to correctly use the 4-corner idle system without it being on top a ProStock engine. They are way too rich.

IMO, if the idle is under 1000 rpm, your method 1 works pretty good with stock calibration. If the idle is 1000 or above, I start with all 4 one turn out and adjust each 1/16" turn for best/smoothest idle.
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  #5  
Old Jun 24th, 08, 7:18 AM
69-CHVL 69-CHVL is online now
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Default Re: 4 corner idle adjustment

Ray, how about just closing the rear mixtures altogether and just running off the front.

Every 4 corner job I did, I always seem to run the rear mixtures in moreso than the front. Keeping the rears even with the front made it way too rich.
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  #6  
Old Jun 24th, 08, 11:51 AM
darkostoj darkostoj is offline
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Default Re: 4 corner idle adjustment

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Originally Posted by 69-CHVL View Post
Ray, how about just closing the rear mixtures altogether and just running off the front.

Every 4 corner job I did, I always seem to run the rear mixtures in moreso than the front. Keeping the rears even with the front made it way too rich.
i was wondering the same thing. I understand how the 4 corner idle is needed for real wild motors, but for a street motor what is the purpose? All I can see it doing is help distribution of idle fuel and keep the fuel in the secondary fuel bowl from becoming stagnant....and thats only if the IFR's are small enough so its not too rich
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Old Jun 24th, 08, 12:47 PM
67RS502 67RS502 is online now
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Default Re: 4 corner idle adjustment

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Originally Posted by 69-CHVL View Post
Ray, how about just closing the rear mixtures altogether and just running off the front.

Every 4 corner job I did, I always seem to run the rear mixtures in moreso than the front. Keeping the rears even with the front made it way too rich.
then what the point of having a 4-corner idle carb?
4-corner really help idle!
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  #8  
Old Jun 24th, 08, 2:58 PM
69-CHVL 69-CHVL is online now
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Default Re: 4 corner idle adjustment

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Originally Posted by 67RS502 View Post
then what the point of having a 4-corner idle carb?
4-corner really help idle!
I think personally that 90% of the cars out there dont need it, and its an unecessary hassle. I think your motor has to be pretty darn radical to need it.
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  #9  
Old Jun 24th, 08, 3:08 PM
creeper72 creeper72 is offline
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Default Re: 4 corner idle adjustment

I would really like to learn more about this, any suggestions?I have a book by Dave Emanuel, it seems to be useless for anything except parts reference.

My car idles right around 1000 rpm in P. Can most agree you want to be about 1/8 turn richer than highest Vaccum on the front screws ?
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  #10  
Old Jun 24th, 08, 3:13 PM
flink69SS flink69SS is offline
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Default Re: 4 corner idle adjustment

I have also spent way too much time trying to figure those 4 corners out.
I am wondering...Those of you that do have your idle mixture "Correct", do you ever really lose that "Running too rich smell" out the exhaust?
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Old Jun 30th, 08, 3:26 PM
creeper72 creeper72 is offline
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Default Re: 4 corner idle adjustment

Any body out there that wants to share some more info ?
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  #12  
Old Jun 30th, 08, 5:17 PM
rednecks70 rednecks70 is offline
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Default Re: 4 corner idle adjustment

Quote:
Originally Posted by creeper72 View Post
Any body out there that wants to share some more info ?
I'd like to know also, I have a used 950HP that is going on my car soon. I finally got my 850VS tuned pretty good so I figure it's time to mess with the 950 and see what performs better. Hopefully someone with expert knowledge will chime in.

P.S. Anybody know what the factory specs are for the 950HP in regards to idle screws and throttle blades?
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  #13  
Old Jun 30th, 08, 6:15 PM
69-CHVL 69-CHVL is online now
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Default Re: 4 corner idle adjustment

Robb, only thing you can do is what Holley suggests: keep all screws equal, looking for highest vac and rpm. Then, I go 1/8 turn each corner looking to really fine-tune everything. Then you may find that the rear screws like to be closed a little moreso than the front. When I had a QuickFuel carb, they said it was OK to run all the screws a little different.

I drive the car around for a long trip, then come back to the garage to make the adjustments. You want the carb and intake as HOT as possible, as this is the true operating temp. Simply letting the car warm up to operating temp is not good - I use that for ball-parking the settings. I connect one of them tach/dwell meters, and keep an eye on it. You would be suprised how an 1/8 of a turn moves the tach, where my factory tach and vac guage dont show that.
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  #14  
Old Jun 30th, 08, 11:48 PM
Camaro_fever68 Camaro_fever68 is offline
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Default Re: 4 corner idle adjustment

Quote:
Originally Posted by 69-CHVL View Post
Ray, how about just closing the rear mixtures altogether and just running off the front.

Every 4 corner job I did, I always seem to run the rear mixtures in moreso than the front. Keeping the rears even with the front made it way too rich.
Quote:
Originally Posted by darkostoj View Post
i was wondering the same thing. I understand how the 4 corner idle is needed for real wild motors, but for a street motor what is the purpose? All I can see it doing is help distribution of idle fuel and keep the fuel in the secondary fuel bowl from becoming stagnant....and thats only if the IFR's are small enough so its not too rich

4-corner idle works excellent if you tune it to the engine. My 4779 750's have 4-corner idle and the mix screws are 1.25 turns out each. The air bleeds and IFR's are not stock though. Most mild engines run better with a 2-corner idle circuit. 4-corner idle is too rich for them. If you try to use a 4-corner idle carb on a mild engine, you end up using very little of the mix screws to tame the A/F idle quality. Then when you drop from park to drive there is a big RPM drop (200+) I don't like the RPM drop. After I tune an engine it shouldn't have no more than a 50 rpm drop between park and drive. Anything more needs more tuning.





Quote:
Originally Posted by flink69SS View Post
I have also spent way too much time trying to figure those 4 corners out.
I am wondering...Those of you that do have your idle mixture "Correct", do you ever really lose that "Running too rich smell" out the exhaust?

Unless you add a cat. and air pump, the exhaust will stink. Bigger the cam, worse it stinks.
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  #15  
Old Jul 1st, 08, 12:16 AM
Dave427 Dave427 is online now
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Default Re: 4 corner idle adjustment

Ok I have used a couple of methods. My AED 750 HO I had on my 383 it was a four corner. I try to keep all 4 screws out all the same number of turns. So I start them all at like 1 1/2 turns out. Warm it up and start at the drivers side front corner turn it in til you hear it sputter a bit then go to the passenger side front, then passenger side rear then back to the drivers side rear. Hopefully when you are done all four screws should be out the same number of turns. If you can turn the rear screws all the way in and nothing happens the front screws are doing all the work. So start all over with the screws all out 1 turn then try again. If you get in a situation like all four screws are only out like less than a 1/2 a turn it will make the idle and off idle too lean. Thats when you can have the back and front mixture screws out a different number of turns. So then I start with the back mixture screws out a 1/2 turn , then adjust the fronts only. If you end up with the fronts say out 3/4 to 1 turn thats cool. The driveability will be better then all the screws only out a 1/2 a turn. I agree with the above 90% of the cars only need 2 mixture screws. The four corners are more meant for really radical idling engines.

Hope that helps

Dave
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