Need help tuning idle circuit
#829414
10/14/10 02:49 AM
10/14/10 02:49 AM
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Joined: Feb 2003
Posts: 265
Garland, Texas
1badmopar
OP
enthusiast
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OP
enthusiast
Joined: Feb 2003
Posts: 265
Garland, Texas
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I have recently finished the 520 build for my '66 Plymouth. Motor runs good, but stumbles / misses off idle. i.e. 1000 - 2000 rpm, then it cleans back up. Since the car has a manual trans, the off idle stumble makes it very challenging to drive. What is the best way to tune the idle circuit? Its a Quickfuel 4150 1050. BTW I have an LM1 wide band if I need it. The 4 corner air bleeds and a vaccum guage seem to not be working very well for me. Thanks. 
1966 Plymouth Belvedere 520" RB w/ Indy 440-1 Heads FiTech Fuel Injection TKO 600 conversion [img] https://flic.kr/p/2j1ejsK[/img]
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Re: Need help tuning idle circuit
[Re: 1badmopar]
#829415
10/14/10 03:10 AM
10/14/10 03:10 AM
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Joined: Aug 2003
Posts: 43,232
Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,232
Bend,OR USA
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Put the wide ban in it and see what it is doing  I like to see around 14.2 to 16.2 at idle and 13.5 to 14.6 at light part throttle cruise, richer(11.8 to 12.9) is more responsive than to lean, (above 16.3 AFR)Be careful, it is always safer to run it a little richer than to lean  Check the front sqirter, see if it squirts as soon as you move the throttle shafts at all, if not adjust that and try again
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Need help tuning idle circuit
[Re: Big Squeeze]
#829418
10/14/10 11:19 AM
10/14/10 11:19 AM
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Joined: Feb 2003
Posts: 265
Garland, Texas
1badmopar
OP
enthusiast
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OP
enthusiast
Joined: Feb 2003
Posts: 265
Garland, Texas
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I am not seeing any of the traditional reaction from the idle air bleed screws, car does not react hardly at all even with the bleeds all the way screwed in or several turns out. Idle is down around 600 rpm.
Doesnt this carb have removable ilde jets on the metering block? If so, what direction should I go to Lean it out? Any suggestions? Also, do I change the high or low side jet? Not sure of the purpose of each?
1966 Plymouth Belvedere 520" RB w/ Indy 440-1 Heads FiTech Fuel Injection TKO 600 conversion [img] https://flic.kr/p/2j1ejsK[/img]
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Re: Need help tuning idle circuit
[Re: 1badmopar]
#829419
10/14/10 11:23 AM
10/14/10 11:23 AM
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Joined: Feb 2003
Posts: 265
Garland, Texas
1badmopar
OP
enthusiast
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OP
enthusiast
Joined: Feb 2003
Posts: 265
Garland, Texas
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It had 35 squirters in fornt and rear. I have changed those to 28 rear and 25 front. Seemed to help a lot with the stumble, but the car is still not right. It is definately still too rich at idle.
1966 Plymouth Belvedere 520" RB w/ Indy 440-1 Heads FiTech Fuel Injection TKO 600 conversion [img] https://flic.kr/p/2j1ejsK[/img]
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Re: Need help tuning idle circuit
[Re: 1badmopar]
#829420
10/14/10 11:29 AM
10/14/10 11:29 AM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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Quote:
I am not seeing any of the traditional reaction from the idle air bleed screws, car does not react hardly at all even with the bleeds all the way screwed in or several turns out. Idle is down around 600 rpm.
Doesnt this carb have removable ilde jets on the metering block? If so, what direction should I go to Lean it out? Any suggestions? Also, do I change the high or low side jet? Not sure of the purpose of each?
The jets really arent your idle jets... where is the
transfer slot(how much is exposed) try opening the
blades a little then see if you can get the mixture
screws to work... you might need a bigger squirter
shot to cover the flat spot on the acceleration
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Re: Need help tuning idle circuit
[Re: 1badmopar]
#829422
10/14/10 08:22 PM
10/14/10 08:22 PM
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Joined: Oct 2007
Posts: 4,209
New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,209
New York
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Stop.
What cam LSA, etc.?
What's your idle vacuum?
What's your initial spark lead?
If vacuum is very low, your transition slot is uncovered too far and it's using the main circuit - which is why the adjustments don't work.
You may need 15-20° advance depending on the cam. Do this first, and start over.
Boffin Emeritus
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Re: Need help tuning idle circuit
[Re: polyspheric]
#829423
10/14/10 10:07 PM
10/14/10 10:07 PM
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Joined: Apr 2006
Posts: 3,675
Akron, Ohio U.S.A.
roadhazard
master
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master
Joined: Apr 2006
Posts: 3,675
Akron, Ohio U.S.A.
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Quote:
Stop.
What cam LSA, etc.?
What's your idle vacuum?
What's your initial spark lead?
If vacuum is very low, your transition slot is uncovered too far and it's using the main circuit - which is why the adjustments don't work.
You may need 15-20° advance depending on the cam. Do this first, and start over.
 check your initial timing. Without 15-20* you can't properly tune the idle circuit on the carb.
I also assume you're turning the "mixture screws" on the metering block and not the "air bleeds" on top the carb correct?
Once the timing is correct you'll be able to close the throttle blades enough (equally because it's a 4 corner idle) to lessen the exposed area of the transfer slots.
Then adjust your "Mixture" screws
Nice looking piece by the way
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Especially on a 520" engine! I'm running 37front and 40rear on my 448" with Mr.P-Body's borrowed 850! Comes off the line with NO hesitation whatsoever! 
