Carburater tuning
#421699
07/28/09 12:25 PM
07/28/09 12:25 PM
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Joined: Jan 2005
Posts: 1,772
Keymar, MD
DusterKid
OP
top fuel
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OP
top fuel
Joined: Jan 2005
Posts: 1,772
Keymar, MD
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What is the quickest and easiest way to tune a carb and get it right (or atleast real close) for your setup? I have a 750 with 78/80 jets, 26 and 31 squriters and not sure of the cams on the carb. I purchased a new 850, put 80 squared jets, put 26 and 31 squirters and it seems to have a stumble to it now? Motor is a standard bore 440 with 440 source alum heads, .533 mopar performance cam, weiland single plane intake, running on 93 octane pump gas. Also for some dumb reason holley has changed their accelarator pumps from the old ball valve to the new rubber seal and they seem to work like junk.
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Re: Carburater tuning
[Re: DusterKid]
#421704
07/28/09 03:28 PM
07/28/09 03:28 PM
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Joined: Aug 2003
Posts: 43,163
Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,163
Bend,OR USA
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Two things you need to do for us to help you, what is the List number of the new 850, IE 4781-? or ??????? and what manifold vacume(not ported, vacume under the butterflys on the carb) do you have idling in gear? The Squirters sizes do sound a little on the small size unless you live where the elevation is above 4500 above sea level
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Carburater tuning
[Re: sshemi]
#421706
07/28/09 03:46 PM
07/28/09 03:46 PM
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Joined: Jan 2005
Posts: 1,772
Keymar, MD
DusterKid
OP
top fuel
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OP
top fuel
Joined: Jan 2005
Posts: 1,772
Keymar, MD
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The carb is a Holley 9380 850 cfm. It came with 78 jets front and rear, and 31 squirters front and rear. It also had a power valve in the front and rear, not sure what they were, but I took those out and plugged them since I never have any luck with power valves. I've adjusted the idleling screws, checked the float levels and added jet extensions with the jet extension float to the rear bowl. With 78/80 in the 750 the car worked great, but seemed to be a little rich, so thats why I didn't upsize jets in the 850. I did have 80/85 in the 850 and it wouldn't idle worth crap.
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Re: Carburater tuning
[Re: DusterKid]
#421707
07/28/09 04:00 PM
07/28/09 04:00 PM
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Joined: Aug 2003
Posts: 43,163
Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,163
Bend,OR USA
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Try starting with 84 jets square with no power valves and see how that works. I like and use power valves in all of the Holley carbs that I own and use that came with them  The big thing on power valves is to use a power valve that is rated to open at least one or two inches under the idle RPM in gear, such as if it idles at 6.0 inches in gear I would use a 4.5 or a 3.5 rated power valve There are some "carb" guru on this site will tell you that the power valve circiut has nothing to do with the idle vacume  , WRONG  Try using a smaller vacume rated power valve in your carb( check the idle vacume and go lower) and go back to the stock jetting and see how that works, let us know if you do and the results
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Carburater tuning
[Re: DusterKid]
#421708
07/28/09 04:02 PM
07/28/09 04:02 PM
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Joined: Aug 2004
Posts: 2,128
sweden
sshemi
top fuel
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top fuel
Joined: Aug 2004
Posts: 2,128
sweden
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Quote:
The carb is a Holley 9380 850 cfm. It came with 78 jets front and rear, and 31 squirters front and rear. It also had a power valve in the front and rear, not sure what they were, but I took those out and plugged them since I never have any luck with power valves. I've adjusted the idleling screws, checked the float levels and added jet extensions with the jet extension float to the rear bowl. With 78/80 in the 750 the car worked great, but seemed to be a little rich, so thats why I didn't upsize jets in the 850. I did have 80/85 in the 850 and it wouldn't idle worth crap.
The main jets have absolutly nothing to do with the idle system.
And if it changes when you change MJs that means your throtle blades are opened too much so you are already in the main system.
Make sure the blades are set correctly.
And if i where you i would use a power valve in front and jet it 78 front and ~86 rear
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Re: Carburater tuning
[Re: sshemi]
#421709
07/28/09 05:25 PM
07/28/09 05:25 PM
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Joined: Jul 2006
Posts: 528
N.W. Indiana
DblOJoe
mopar
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mopar
Joined: Jul 2006
Posts: 528
N.W. Indiana
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Quote:
The main jets have absolutly nothing to do with the idle system.
And if it changes when you change MJs that means your throtle blades are opened too much so you are already in the main system.
Make sure the blades are set correctly.
And if i where you i would use a power valve in front and jet it 78 front and ~86 rear
 I'd put the 31 squirter back in the front also.
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Re: Carburater tuning
[Re: DusterKid]
#421710
07/29/09 11:47 AM
07/29/09 11:47 AM
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Joined: Oct 2007
Posts: 4,206
New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,206
New York
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I took those out and plugged them since I never have any luck with power valves.....
Boffin Emeritus
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