Re: Do I have a vacuum leak?
[Re: Moparmaniacc]
#2980360
10/31/21 08:29 PM
10/31/21 08:29 PM
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Joined: Nov 2003
Posts: 10,228 Colleyville
3hundred
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I Live Here
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Posts: 10,228
Colleyville
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Sounds like the rings haven't yet seated? Did you degree the cam or just match the dots? IIRC, and it's been a LONG time, Holley's come with a 12.5 HG power valve and you're only pulling 10 HG? So the PV is open the entire time you're idling?
'68 Fury Convertible '69 300 Convertible '15 Durango 5.7 Hemi '16 300 S Hemi
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Re: Do I have a vacuum leak?
[Re: TJP]
#2980369
10/31/21 08:58 PM
10/31/21 08:58 PM
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Joined: Nov 2003
Posts: 10,228 Colleyville
3hundred
I Live Here
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I Live Here
Joined: Nov 2003
Posts: 10,228
Colleyville
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Sounds like the rings haven't yet seated? Did you degree the cam or just match the dots? IIRC, and it's been a LONG time, Holley's come with a 12.5 HG power valve and you're only pulling 10 HG? So the PV is open the entire time you're idling? has holley changed? used to all be 6.5's. BTW I have b-tt load of new ones LOL I think I removed my 6 barrel setup in the early '80's? I'm just not sure anymore. My memory for details like that is failing. But isn't the PV the usual culprit for rich idle mixtures?
'68 Fury Convertible '69 300 Convertible '15 Durango 5.7 Hemi '16 300 S Hemi
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Re: Do I have a vacuum leak?
[Re: 3hundred]
#2980370
10/31/21 08:58 PM
10/31/21 08:58 PM
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Joined: Apr 2006
Posts: 4,220 West Plains, MO
DrCharles
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Joined: Apr 2006
Posts: 4,220
West Plains, MO
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Sounds like the rings haven't yet seated? Did you degree the cam or just match the dots? IIRC, and it's been a LONG time, Holley's come with a 12.5 HG power valve and you're only pulling 10 HG? So the PV is open the entire time you're idling? PV enriches the mains only, not the idle circuit. Doesn't matter if it's open at idle or not. My 451 idles at 8" Hg and the idle AFR and RPM stay the same whether I have a 10.5 or 7.5 PV. Incidentally there's another urban legend, which Holley is still perpetuating, that your PV should be 2" below idle vacuum. Which is pure bull. You want it to be several inches below cruise vacuum - the exact point has to be determined by experiment and a wide-band AFR meter to assist. My cruise vacuum is 14-15", and I'm still trying to decide whether the 7.5 or 8.5 feels better on the butt-dyno. I tried a 10.5 but it was coming in too early, just making things overrich. Remember you want the mixture to go leaner at part-throttle, until somewhere above 50% of max power (this point on the curve is different for every engine and induction system).
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Re: Do I have a vacuum leak?
[Re: Moparmaniacc]
#2980739
11/01/21 10:13 PM
11/01/21 10:13 PM
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Joined: Oct 2005
Posts: 4,956 WI
Dcuda69
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WI
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You are right, Holley says you should have a little bit of transfer slot showing at idle. So for all you guys out there with a mild or stock cam, how much vacuum are you pulling at idle? thanks 470" low deck,10.2:1, Comp XR280R (242/248@.050)solid roller pulls 10-12" and idles nicely at 900 rpm with a Holley 800 DP that's essentially untouched.
Last edited by Dcuda69; 11/01/21 10:16 PM.
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Re: Do I have a vacuum leak?
[Re: Dcuda69]
#2980802
11/02/21 08:44 AM
11/02/21 08:44 AM
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Joined: May 2019
Posts: 6,291 nowhere
Sniper
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Posts: 6,291
nowhere
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You are right, Holley says you should have a little bit of transfer slot showing at idle. So for all you guys out there with a mild or stock cam, how much vacuum are you pulling at idle? thanks 470" low deck,10.2:1, Comp XR280R (242/248@.050)solid roller pulls 10-12" and idles nicely at 900 rpm with a Holley 800 DP that's essentially untouched. Pretty sure that cam isn't "mild or stock". My 51 pulls 20" at idle, bone stock. But's it's a flathead six and just about as relevant.
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Re: Do I have a vacuum leak?
[Re: Dcuda69]
#2980829
11/02/21 10:16 AM
11/02/21 10:16 AM
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Joined: Jun 2014
Posts: 3,216 Md.
carnut68
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Md.
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What is your timing at idle? Do you vacuum advance or mechanical? Check the gasket under the pv to make sure it was installed correctly. Check the gaskets under the carb for good seal.
America First!
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Re: Do I have a vacuum leak?
[Re: TJP]
#2980889
11/02/21 12:50 PM
11/02/21 12:50 PM
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Joined: Aug 2003
Posts: 43,251 Bend,OR USA
Cab_Burge
I Win
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I Win
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Posts: 43,251
Bend,OR USA
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Last edited by Cab_Burge; 11/03/21 03:27 AM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Do I have a vacuum leak?
[Re: Cab_Burge]
#2981079
11/02/21 08:45 PM
11/02/21 08:45 PM
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Joined: Apr 2006
Posts: 4,220 West Plains, MO
DrCharles
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West Plains, MO
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No transfer slot visible means the t-slot isn't flowing at idle. So it'll take time to get flowing as you crack open the throttle. This results in an off-idle sag or stumble. You can partially cover it up with enough pump squirt. I suppose with a loose enough converter it won't be noticeable either. It definitely is with a four-speed and a lot of cam. Also, with any kind of bigger cam, there may not be enough air coming through with the throttles closed that far. You can also cover that up by cracking the secondaries... Of course if all you're interested in is idle and WOT on the strip, it's no problem! But there's a lot more tuning involved to have good tip-in and cruise manners on the street. May I recommend the RFS Holley forum.
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