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Author
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Topic: cause of of-the-line stumble
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Rustang
Gearhead Posts: 733
From: Clarion PA
Registered: Nov 2000
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posted 11-03-2004 12:39 PM
   
I'm trying to get my car to 60 foot better, and one thing I've noticed on my playback tach is a consistent "dead spot" on launch. I foot brake to 3500rpm, and when I nail it the converter stops at 4500rpm for a split second before flashing to it's stall speed of 5000rpm. There's no wheel-spin, and 60' times are around 1.66-1.69. I suspect it's in the pump-shot(750dp), but I don't know to go with more or less. Right now I have a 31 in the primary and a 35 in the secondary. I'm thinking aobut first trying to switch them around, or maybe go with 35's all around? Any thoughts? ------------------
'68 mustang 351 clevor- 10.92@124
'67 Stang, 351W -11.18@118
'69 351C Torino-14.90@100
'78 Pickup 351W-15.56@88
'79 Pickup 460 ET=??
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capri man
Gearhead Posts: 6417
From: doerun, ga.
Registered: Nov 2000
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posted 11-03-2004 01:02 PM
i got 42.s in my 700 if that helps any!! 
good luck------------------
mike r
racing is real
everything else is just a game.
81 capri-302-7.33 @92mph 1/8
1.54 60 ft. http://community.prestage.com/Member+Pages/789.aspx
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Fordwiser
Gearhead Posts: 390
From: Metamora, Illinois
Registered: Dec 2000
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posted 11-03-2004 05:48 PM
Bigger squirters may or may not help, it could be that since you allready have the throttle open some the lever may already be up on the pump cam causing you to loose some of the shot duration, sometimes you can change to the different screw position to change the cam position. Different pump cams have different durations, some people even grind on the plastic cams to get what they need, sometimes you can even drill your own hole in cam to tune the pump shot.Roger
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Rustang
Gearhead Posts: 733
From: Clarion PA
Registered: Nov 2000
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posted 11-03-2004 05:53 PM
Thanks....
I am running advance on the cam on the primary. Actually it stumbles a bit because of that when I stab it from a dead idle. but when I bring it up against the brake I'm assuming I'm up on the cam enough that it won't stumble... 
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Fordwiser
Gearhead Posts: 390
From: Metamora, Illinois
Registered: Dec 2000
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posted 11-03-2004 06:09 PM
This may sound crazy, but try unhooking the secondaries and launch it with only the primaries, if it launches better it could be a problem on the secondary side, if it's the same you'll know it's the primaries.Roger
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Moneymaker
Administrator Posts: 25883
From: Lyons, IL, USA
Registered: May 99
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posted 11-03-2004 06:18 PM
Are you using power valves?------------------
Alex Denysenko
Co-Administrator and Moderator NHRA/IHRA/SRA member and licensed Superstock driver
MCA member# 53321
NHRA and IHRA SS/LA & SS/MA National Record Holder '00,'01,'02,'03,& '04
First SS/MA in the TENS!
IHRA division 5 Superstock Champion
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28 The Barry of BarrysGrrl Quote #1: "I never met a magazine mechanic I liked."
Quote #2: "Make sure brain is in gear before engaging mouth!"
Quote #3: "If you can't run with the big dogs, stay on the porch!"
www.moneymakerracing.com
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rustang@home
Journeyman Posts: 94
From: Clarion, PA
Registered: Jan 2004
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posted 11-03-2004 09:12 PM
quote:
Originally posted by Moneymaker:
Are you using power valves?
yep. In the primary only. I think it's a 6.5 (I've been told to get rid of the power valve entirely but don't know if that's a good thing or not.)
BTW I'm running 75's in the primary, and I think 79's in the secondary.
[This message has been edited by rustang@home (edited 11-03-2004).]
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Moneymaker
Administrator Posts: 25883
From: Lyons, IL, USA
Registered: May 99
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posted 11-03-2004 10:33 PM
Lose the power valve and richen up the primary 20%.------------------
Alex Denysenko
Co-Administrator and Moderator NHRA/IHRA/SRA member and licensed Superstock driver
MCA member# 53321
NHRA and IHRA SS/LA & SS/MA National Record Holder '00,'01,'02,'03,& '04
First SS/MA in the TENS!
IHRA division 5 Superstock Champion
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28 The Barry of BarrysGrrl Quote #1: "I never met a magazine mechanic I liked."
Quote #2: "Make sure brain is in gear before engaging mouth!"
Quote #3: "If you can't run with the big dogs, stay on the porch!"
www.moneymakerracing.com
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Mike_R
Gearhead Posts: 176
From: Indianapolis, IN 46237
Registered: Feb 2001
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posted 11-04-2004 08:05 AM
Do you have jet extensions in the rear?
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Rustang
Gearhead Posts: 733
From: Clarion PA
Registered: Nov 2000
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posted 11-04-2004 09:48 AM
I've got the jet extensions. I'm going to try getting rid of the power valve. So if I go with 79 jets all around for starters? Does that sound in the ballpark for an off the shelf old 750dp?
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