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CARB EXPERTS ? IFR/IAB #828510
10/12/10 09:29 PM
10/12/10 09:29 PM
Joined: Dec 2008
Posts: 52
detroit mich
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stevehiss Offline OP
member
stevehiss  Offline OP
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Joined: Dec 2008
Posts: 52
detroit mich
can anyone school me on what occurs when the IFR is made smaller or bigger in relationship to the IAB .

i seem to have a really lean idle in a carb i sold to my buddy .


thanks


I DARE TO BE DIFFERENT
Re: CARB EXPERTS ? IFR/IAB [Re: stevehiss] #828511
10/12/10 09:41 PM
10/12/10 09:41 PM
Joined: Dec 2008
Posts: 1,200
UK
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602heavy Offline
pro stock
602heavy  Offline
pro stock
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Joined: Dec 2008
Posts: 1,200
UK
Increasing the size of idle fuel restrictor will fatten up idle/transition circuits , increasing idle air bleeds will lean out idle/transition circuits , increasing/decreasing by .003" will have a noticeable effect.


Re: CARB EXPERTS ? IFR/IAB [Re: stevehiss] #828512
10/12/10 10:22 PM
10/12/10 10:22 PM
Joined: Jan 2003
Posts: 11,892
Benton, IL.
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DaveRS23 Offline
Special needs idiot
DaveRS23  Offline
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Joined: Jan 2003
Posts: 11,892
Benton, IL.
I agree with the above.

It may help to think of the IFR as the idle main jet. It meters the fuel on the idle circuit. Larger orifice = more fuel, smaller = less.

And think of the IAB as idle jets for the air. This time a larger orifice opening means more air in relation to the fuel, aka leaner, while a smaller orifice results in less air and a richer idle mixture.

You may use a little caution when messing with the air bleeds because they also affect when the main fuel circuit activates.

Do you have a wide-band O2? They help a lot not just to let you know mixture, but when each circuit comes and goes and what effect your changes have on each.

If you have any off-idle issues, don't forget about the transition slots.

If you already know all this, my apologies. I just hope to make you aware that idle and off-idle tuning is the most complicated because there are several circuits overlapping.



Master, again and still
Re: CARB EXPERTS ? IFR/IAB [Re: stevehiss] #828513
10/12/10 11:22 PM
10/12/10 11:22 PM
Joined: Dec 2008
Posts: 52
detroit mich
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stevehiss Offline OP
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stevehiss  Offline OP
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Joined: Dec 2008
Posts: 52
detroit mich
thanks for the info,
i swapped some billet metering blocks into my friends carb and the car would no longer idle.i had to go from 71 IAB to 55 IAB to ge it to idle . i see the IFR is smaller in the billet blocks than the IFR in thr stock blocks.


I DARE TO BE DIFFERENT
Re: CARB EXPERTS ? IFR/IAB [Re: stevehiss] #828514
10/13/10 01:43 AM
10/13/10 01:43 AM
Joined: Aug 2003
Posts: 43,007
Bend,OR USA
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Cab_Burge Offline
I Win
Cab_Burge  Offline
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Bend,OR USA
You can try some very small diameter wire in the IAB to see how much that helps, the other thing is the idle mixture screws and throttle blades opening, front and rear Let us know what ends up working


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)






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