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Author Topic:   Getting the Idle down!
68 S-code GT
Gearhead

Posts: 2416
From: Sayreville, NJ, US
Registered: Mar 2000

posted 07-08-2002 07:40 AM     Click Here to See the Profile for 68 S-code GT   Click Here to Email 68 S-code GT     Edit/Delete Message   Reply w/Quote
Looking for some ideas of what to do! Itís a stock 66-289 with an iron 68-4V intake along with a 69-600cfm 4300 carb on top and headers. I think its idling around 1200-1300 because my Tack/Dwell meter stops at 1200 and the needle is fluctuating. I canít get it down any further, is there something not installed correctly on the carb or an adjustment Iím missing? I thought it might be the fast idle adjustment but I have the screw backed off all the way along with the primary idle adjustment! The timing is set at about 6 deg. for now.

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68 S-code FB GT 4spd(now C6)/3.25 PS PDB
68 J-code(now 289) Cp Sprint"B" C4/3L00-9" PDB PS AC
99 F150 XLT Ext/cab, 4X4, 5.4L, 3L55
95 Explorer XLT with the works! (Wifeís car)

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Jeff
Gearhead

Posts: 306
From: Moore, OK USA
Registered: Mar 2001

posted 07-08-2002 03:24 PM     Click Here to See the Profile for Jeff   Click Here to Email Jeff     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Jeff:
My guess is the linkage is hung up on the side of the intake manifold. With some carbs on some manifolds, the right side of the linkage does not clear the manifold and hence does not allow the primary butterflies to fully close. Try loosing the carb bolts and pushing the carb hard towards the passenger side. This small extra clearance often frees the bound linkage. Use a carb spacer if this doesn't free the linkage.

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SteveLaRiviere
Administrator

Posts: 42859
From: Saco, Maine
Registered: May 99

posted 07-08-2002 07:25 PM     Click Here to See the Profile for SteveLaRiviere   Click Here to Email SteveLaRiviere     Edit/Delete Message   Reply w/Quote
Things to check:

*Weak return spring. Try moving the throttle closed as see if that slows idle.

*Vacuum leak. Can you stall the engine by blocking the choke housing with your hand? If you can't, you have a vacuum leak.

*Excessive clearance between throttle shaft and throttle shaft bore in base plate. See if you can make the idle speed go up and down by moving the throttle shaft. Excessive clearance here causes a vacuum leak, raising idle speed.

*Loose carb, causing vacuum leak.

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'70 Mustang Mach 1, '72 Mustang Sprint, '94 F-150
Pics

MCA Member # 47773

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68 S-code GT
Gearhead

Posts: 2416
From: Sayreville, NJ, US
Registered: Mar 2000

posted 07-08-2002 09:48 PM     Click Here to See the Profile for 68 S-code GT   Click Here to Email 68 S-code GT     Edit/Delete Message   Reply w/Quote
Itís not the spring because I have that off along with the linkage it connects to.

The engine stalls out if I close the choke up so I guess there is no vacuum leak.

Iíll have to check the throttle shaft but I have to pull the pan first. Whoever built the engine put the oil drive shaft in upside down. I just pulled the distributor so I could jump it over one more tooth and I heard a clank. The shaft pulled up out of the pump and fell into the pan. At least I now have a good excuse to check out the bottom end.

quote:
Originally posted by SteveLaRiviere:
Things to check:

*Excessive clearance between throttle shaft and throttle shaft bore in base plate. See if you can make the idle speed go up and down by moving the throttle shaft. Excessive clearance here causes a vacuum leak, raising idle speed.


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68 S-code GT
Gearhead

Posts: 2416
From: Sayreville, NJ, US
Registered: Mar 2000

posted 07-08-2002 09:53 PM     Click Here to See the Profile for 68 S-code GT   Click Here to Email 68 S-code GT     Edit/Delete Message   Reply w/Quote
It looks free of any obstruction but Iíll try your idea anyway!
If that doesnít work or Steveís idea I guess Iíll pull the carb and try to see if the butterflies can be adjusted at all.


quote:
Originally posted by Jeff:

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Moneymaker
Administrator

Posts: 25539
From: Lyons, IL, USA
Registered: May 99

posted 07-09-2002 02:13 PM     Click Here to See the Profile for Moneymaker   Click Here to Email Moneymaker     Edit/Delete Message   Reply w/Quote
Check the SECONDARY throttle adjustment. They are probably open a touch. You need to remove the carb to adjust the set screw.

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Alex Denysenko
Co-Administrator and Moderator/ non 65-66 Mustang owner sensitivity co-ordinator

NHRA/IHRA/SRA member
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SteveLaRiviere
Administrator

Posts: 42859
From: Saco, Maine
Registered: May 99

posted 07-09-2002 08:14 PM     Click Here to See the Profile for SteveLaRiviere   Click Here to Email SteveLaRiviere     Edit/Delete Message   Reply w/Quote
I was gonna say that next...

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'70 Mustang Mach 1, '72 Mustang Sprint, '94 F-150
Pics

MCA Member # 47773

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Moneymaker
Administrator

Posts: 25539
From: Lyons, IL, USA
Registered: May 99

posted 07-09-2002 10:17 PM     Click Here to See the Profile for Moneymaker   Click Here to Email Moneymaker     Edit/Delete Message   Reply w/Quote

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Alex Denysenko
Co-Administrator and Moderator/ non 65-66 Mustang owner sensitivity co-ordinator

NHRA/IHRA/SRA member
NHRA and IHRA SS/LA National Record Holder '00, '01, & '02
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Part time secret agent license #0089
Professional Manwhore
The Barry of BarrysGrrl

IP: Logged

68 S-code GT
Gearhead

Posts: 2416
From: Sayreville, NJ, US
Registered: Mar 2000

posted 07-10-2002 07:42 AM     Click Here to See the Profile for 68 S-code GT   Click Here to Email 68 S-code GT     Edit/Delete Message   Reply w/Quote
Where exactly is it? I was initially thinking of that but this is the first 4300 that Iíve ever played with so Iím a little lost!
quote:
Originally posted by Moneymaker:
Check the SECONDARY throttle adjustment. They are probably open a touch. You need to remove the carb to adjust the set screw.


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Moneymaker
Administrator

Posts: 25539
From: Lyons, IL, USA
Registered: May 99

posted 07-10-2002 10:53 AM     Click Here to See the Profile for Moneymaker   Click Here to Email Moneymaker     Edit/Delete Message   Reply w/Quote
Passenger (choke) side in the throttle body, underneath. It is a set screw that hits a part of choke linkage that connects to the secondary. You have to pull the carb and turn it upside down.

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Alex Denysenko
Co-Administrator and Moderator/ non 65-66 Mustang owner sensitivity co-ordinator

NHRA/IHRA/SRA member
NHRA and IHRA SS/LA National Record Holder '00, '01, & '02
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Part time secret agent license #0089
Professional Manwhore
The Barry of BarrysGrrl

IP: Logged

68 S-code GT
Gearhead

Posts: 2416
From: Sayreville, NJ, US
Registered: Mar 2000

posted 08-06-2002 07:26 AM     Click Here to See the Profile for 68 S-code GT   Click Here to Email 68 S-code GT     Edit/Delete Message   Reply w/Quote
Well, I finally got the new pump and oil pan on the engine and instead of messing around with the 4300 I installed the 1850 from my FB on the coupe. It ran perfectly. I will still have to fine tune it but I guess my problem with the 4300 is with the throttle shaft. Is it the base that wares or the shaft?

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Moneymaker
Administrator

Posts: 25539
From: Lyons, IL, USA
Registered: May 99

posted 08-06-2002 10:20 AM     Click Here to See the Profile for Moneymaker   Click Here to Email Moneymaker     Edit/Delete Message   Reply w/Quote
Usually both.

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Alex Denysenko
Co-Administrator and Moderator/ non 65-66 Mustang owner sensitivity co-ordinator

NHRA/IHRA/SRA member
NHRA and IHRA SS/LA National Record Holder '00, '01, & '02
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Part time secret agent license #0089
Professional Manwhore
The Barry of BarrysGrrl

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