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Author Topic:   Engine stumbles when braking
bluestreek
Gearhead

Posts: 1289
From: Athens,GA
Registered: Jul 2001

posted 11-14-2002 07:04 PM     Click Here to See the Profile for bluestreek   Click Here to Email bluestreek     Edit/Delete Message   Reply w/Quote
I have a new Holley 750 HP carb, 2" spacer, and Stealth 8020 on my 331 stroker. The engine is really bad about dying or stumbling when I come to a stop before the engine is hot. It cranks right up afterwards and idles fine. It does get better after the engine is fully warmed up. Otherwise it haulz ballz! The street roller idles good with 14" of vacuum and engine is VERY responsive to any amount of throttle. Any ideas as to what may be causing the stumble when letting off the gas and stopping?

Thanks.

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1966 Mustang Coupe: Custom glass hood and BIG scoop sits atop a 289 stroked to 331 c.i., Steel crank and girdle, 5.4 H-beams, Forged slugs, ported TFS alum. heads, ported Stealth 8020 intake, CompCams Xtreme Solid Roller, Holley 750 HP, long tubes, 4speed, 9" 3.50 posi, BFG Drag radials..

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Moneymaker
Administrator

Posts: 19704
From: Lyons, IL, USA
Registered: May 99

posted 11-14-2002 08:47 PM     Click Here to See the Profile for Moneymaker   Click Here to Email Moneymaker     Edit/Delete Message   Reply w/Quote
Sounds like the floats may be too low. Set them with the engine running and electric pump on. Make sure you have no more than 7 psi of fuel pressure.

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Alex Denysenko
Co-Administrator and Moderator

NHRA/IHRA/SRA member and licensed Superstock driver
MCA member# 53321
NHRA and IHRA SS/LA National Record Holder '00, '01, & '02
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Professional Manwhore
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!"

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bluestreek
Gearhead

Posts: 1289
From: Athens,GA
Registered: Jul 2001

posted 11-14-2002 09:15 PM     Click Here to See the Profile for bluestreek   Click Here to Email bluestreek     Edit/Delete Message   Reply w/Quote
I've been meaning to get a pressure guage for the fuel. I checked the bowls and the rear bowl is barely seeping out and the front bowl has to be shaken a little to get gas outta the hole.

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1966 Mustang Coupe: Custom glass hood and BIG scoop sits atop a 289 stroked to 331 c.i., Steel crank and girdle, 5.4 H-beams, Forged slugs, ported TFS alum. heads, ported Stealth 8020 intake, CompCams Xtreme Solid Roller, Holley 750 HP, long tubes, 4speed, 9" 3.50 posi, BFG Drag radials..

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Moneymaker
Administrator

Posts: 19704
From: Lyons, IL, USA
Registered: May 99

posted 11-14-2002 09:43 PM     Click Here to See the Profile for Moneymaker   Click Here to Email Moneymaker     Edit/Delete Message   Reply w/Quote
Floats should be trickling out over the sight holes at idle.

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Alex Denysenko
Co-Administrator and Moderator

NHRA/IHRA/SRA member and licensed Superstock driver
MCA member# 53321
NHRA and IHRA SS/LA National Record Holder '00, '01, & '02
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Professional Manwhore
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!"

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bluestreek
Gearhead

Posts: 1289
From: Athens,GA
Registered: Jul 2001

posted 11-14-2002 10:18 PM     Click Here to See the Profile for bluestreek   Click Here to Email bluestreek     Edit/Delete Message   Reply w/Quote
Thanks Alex, I'll set the front float 2morrow. That sounds like it could be the problem.

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1966 Mustang Coupe: Custom glass hood and BIG scoop sits atop a 289 stroked to 331 c.i., Steel crank and girdle, 5.4 H-beams, Forged slugs, ported TFS alum. heads, ported Stealth 8020 intake, CompCams Xtreme Solid Roller, Holley 750 HP, long tubes, 4speed, 9" 3.50 posi, BFG Drag radials..

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Dusty Kiser
Gearhead

Posts: 126
From: Bethel,Oh USA
Registered: Mar 2002

posted 11-16-2002 07:45 PM     Click Here to See the Profile for Dusty Kiser   Click Here to Email Dusty Kiser     Edit/Delete Message   Reply w/Quote
Blustreek, that HP has 4 corner idle. Make sure all 4 are set properly (Alex has covered the proceedure on a previous thread). Also, on rare occasions violent braking can cause fuel to slosh out the bowl vents into the carb throat and actually flood it. Good luck

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bluestreek
Gearhead

Posts: 1289
From: Athens,GA
Registered: Jul 2001

posted 11-16-2002 09:02 PM     Click Here to See the Profile for bluestreek   Click Here to Email bluestreek     Edit/Delete Message   Reply w/Quote
I've spent a few hours playing with the jets and floats and haven't had time to final tune the 4-corner idle yet. So far so good. I did found out that the front idle screw will compensate for the back and vice-versa. It's probably unecessary on a engine at my rpm level . I also found out from test and tune that the carb runs leaner and sweeter if I leave the breather assy on. I have a 1" spacer above the carb to get the breather up in the scoop and it seems to like it.
I also have a 2" 4-hole spacer beneath the carb. Do you guys think I might be better off with a 2" neck above the carb and a 1" spacer below?.

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1966 Mustang Coupe: Custom glass hood and BIG scoop sits atop a 289 stroked to 331 c.i., Steel crank and girdle, 5.4 H-beams, Forged slugs, ported TFS alum. heads, ported Stealth 8020 intake, CompCams Xtreme Solid Roller, Holley 750 HP, long tubes, 4speed, 9" 3.50 posi, BFG Drag radials..

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