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Author Topic:   Stumble help, please
Fastymz
Moderator

Posts: 14201
From: Reno Nv USA MEM#1240
Registered: Apr 2001

posted 01-29-2003 02:52 AM     Click Here to See the Profile for Fastymz   Click Here to Email Fastymz     Edit/Delete Message   Reply w/Quote
My car started alte this summer to stumble.It is mostly at idle and at 2-3000 rpm,only when your cruising.Never when your on it.
At idle it the tach will jump down about 2-300rpm,and you can really feel the car stumble.
And then again once I get to cruising speed.at abouyt 2-3000rpm the car misses alittle,then it's fine.
And at idle it only does it once in while.Some times it will go away and come back day.Today it was doing real bad from idle driving and cruising.Then I got on it,and it would not do it again?

Few things I did,I got new Ford 9mm plug wires,a new wide cap & new rotor.New pretronix II coil.

I did check the carb for leaks.I found that the thortle shafts both front and rear.When I sprayed carb cleaner on then it would make the car run rough.So there is a leak there? could that be the problem.
Or is it another bad pretronix unit.I just got the pretronixII unit this spring.

So tell me what you guys think.

------------------
SCOOP
oddly obsessed with big scoops on little Mustangs

2.26 60'S
14.9 @ 90.86MPH

65 coupe,351w,C4,Big Boss 429 hood scoop,8"3.40 TracLoc,Cragar SS,Black Suede.

https://mustangsandmore.com/ubb/Fastymz.html

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SteveLaRiviere
Administrator

Posts: 37258
From: Saco, Maine
Registered: May 99

posted 01-29-2003 08:11 AM     Click Here to See the Profile for SteveLaRiviere   Click Here to Email SteveLaRiviere     Edit/Delete Message   Reply w/Quote
Spray WD-40 on the throttle shafts, not carb cleaner. You don't want to wash the lube away.

Your problem does sound like a lean condition, by either vacuum leak or jetting. Remember, colder air wants more fuel.

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

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V8 Thumper
Gearhead

Posts: 4044
From: Orange, Ca. United States of America
Registered: Dec 2001

posted 01-29-2003 09:00 AM     Click Here to See the Profile for V8 Thumper   Click Here to Email V8 Thumper     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by SteveLaRiviere:
colder air wants more fuel.


Absolutely. 200-300 is a big stumble IMO; I wonder if your squirter has gunk in it. What # jets and squirter are in it?

------------------
1965 GT coupe, 333ci aluminum headed/solid cammed stroker, four speed, 3.70:1 9"

All Blue Oval, no blue bottle
http://mustangsandmore.50megs.com/V8Thumper.html

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SteveLaRiviere
Administrator

Posts: 37258
From: Saco, Maine
Registered: May 99

posted 01-29-2003 09:18 AM     Click Here to See the Profile for SteveLaRiviere   Click Here to Email SteveLaRiviere     Edit/Delete Message   Reply w/Quote
I suspect that with Ron getting 16 mpg, he's running it pretty lean.

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

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V8 Thumper
Gearhead

Posts: 4044
From: Orange, Ca. United States of America
Registered: Dec 2001

posted 01-29-2003 09:23 AM     Click Here to See the Profile for V8 Thumper   Click Here to Email V8 Thumper     Edit/Delete Message   Reply w/Quote
16??? That's double what I get

------------------
1965 GT coupe, 333ci aluminum headed/solid cammed stroker, four speed, 3.70:1 9"

All Blue Oval, no blue bottle
http://mustangsandmore.50megs.com/V8Thumper.html

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bluestreek
Gearhead

Posts: 1460
From: Athens,GA
Registered: Jul 2001

posted 01-29-2003 11:06 AM     Click Here to See the Profile for bluestreek   Click Here to Email bluestreek     Edit/Delete Message   Reply w/Quote
Have you tried increasing the base timing or using a vacuum advance. These things can help sometimes on the street. I'm able to run my 331 with 18 degrees base timing with really quick advance springs, but that's with Alum. heads. Also pay close attention to the squirters. They should react with the slightest touch of the throttle. If not, then make sure the check valve under the squirter isn't allowing the fuel to leak back down. Adjust the the pump spring to make sure the cam stays against the pump arm. If the carb has a lot miles on it, make sure the throttle arm isn't loose on the shaft. Check your float level. The fuel level needs to be up to the sight hole. Finally, set the idle mixture for the highest rpms. If nothing seems to help the stumble, then you can try going up 2-3 numbers on the jets. We gained 2 tenths of a second on a 351 last Fall by increasing the jet sizes by 3 numbers on a 600 DP (72/80). We thought it was rich, but the numbers proved otherwise.

Good luck with it.

------------------
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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Fastymz
Moderator

Posts: 14201
From: Reno Nv USA MEM#1240
Registered: Apr 2001

posted 01-29-2003 11:23 AM     Click Here to See the Profile for Fastymz   Click Here to Email Fastymz     Edit/Delete Message   Reply w/Quote
I got the 16mpg when the car was lean late this summer.I changed to a #69 front jets and #75 rear,thats up six jets sizes.The plug dont look lean to me.
The power valve is a #6.5,and the squiter is a #31.
It was about 60 degrees out yesterday.
Some reason I think it's more in the ign,but the starts fine and runs fine most of the time?

So tell me what you think about the carb and or ign.
And what can I test or look for.

Thanks for all the help,time after time.
And Alex I asked my dog about this and he didn't know,or at least he wasn't telling.

------------------
SCOOP
oddly obsessed with big scoops on little Mustangs

2.26 60'S
14.9 @ 90.86MPH

65 coupe,351w,C4,Big Boss 429 hood scoop,8"3.40 TracLoc,Cragar SS,Black Suede.

https://mustangsandmore.com/ubb/Fastymz.html

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Fastymz
Moderator

Posts: 14201
From: Reno Nv USA MEM#1240
Registered: Apr 2001

posted 01-29-2003 11:30 AM     Click Here to See the Profile for Fastymz   Click Here to Email Fastymz     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by bluestreek:
Have you tried increasing the base timing or using a vacuum advance.

'Base timing is at 16 and all in at 34,at 2500rpm.'

Also pay close attention to the squirters. They should react with the slightest touch of the throttle.

'Yes it seems work fine?'

If the carb has a lot miles on it, make sure the throttle arm isn't loose on the shaft.

'They seem alittle lose'

Check your float level.

'Level is good now.'

Finally, set the idle mixture for the highest rpms.

'I have set it twice or more it's the best I can get it.'


Good luck with it.

'Thanks for the suggestions. '
Ron


------------------
SCOOP
oddly obsessed with big scoops on little Mustangs

2.26 60'S
14.9 @ 90.86MPH

65 coupe,351w,C4,Big Boss 429 hood scoop,8"3.40 TracLoc,Cragar SS,Black Suede.

https://mustangsandmore.com/ubb/Fastymz.html

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Moneymaker
Administrator

Posts: 21725
From: Lyons, IL, USA
Registered: May 99

posted 01-29-2003 11:38 AM     Click Here to See the Profile for Moneymaker   Click Here to Email Moneymaker     Edit/Delete Message   Reply w/Quote
Put a 4.5 power valve in the carb.

------------------
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,&'03
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!"
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rockafellz
Gearhead

Posts: 1348
From: San Lorenzo, CA, USA
Registered: Aug 2001

posted 01-29-2003 11:55 AM     Click Here to See the Profile for rockafellz   Click Here to Email rockafellz     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by V8 Thumper:
16??? That's double what I get


Yeah, almost triple what I get.

Erik

------------------
1966 Ford Mustang 2+2
Mine - Restomod in Progress

1966 Ford Mustang Coupe
Dad's - Original Unrestored

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Fastymz
Moderator

Posts: 14201
From: Reno Nv USA MEM#1240
Registered: Apr 2001

posted 01-29-2003 12:22 PM     Click Here to See the Profile for Fastymz   Click Here to Email Fastymz     Edit/Delete Message   Reply w/Quote
I think stumble was the wrong word sorry,it more of a surge,or just plain power loss.When it happens at idle it drops about 2-300rpm,and you can really feel the car missing,like it bumps the car alittle.
And then again I get it when I let off the gas to cruise,just a little stumble.

Sorry if stumble was the wrong word,because it doesn't do it when I accelerate,only at idle and then again when you get out of gas.

Thanks,
Alex if you still think the 4.5 will help I'll try it.My car makes like 17" of vacuum at idle,doesn't that make a difference as to what power valve to run?

I'm going to call pretronix today to and talk to them about new systemII I got this spring.

------------------
SCOOP
oddly obsessed with big scoops on little Mustangs

2.26 60'S
14.9 @ 90.86MPH

65 coupe,351w,C4,Big Boss 429 hood scoop,8"3.40 TracLoc,Cragar SS,Black Suede.

https://mustangsandmore.com/ubb/Fastymz.html

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Hans olsson
Gearhead

Posts: 385
From: Sweden
Registered: Apr 2000

posted 01-29-2003 02:18 PM     Click Here to See the Profile for Hans olsson   Click Here to Email Hans olsson     Edit/Delete Message   Reply w/Quote
Look down in the carb with the motor at idle and check for fuel coming from the boosters.
There should be no fuel coming from them at idle. Be careful when you have the air cleaner off in case of a backfire.
Tell us what you saw.

------------------

  • 71 Mach1 351c
  • E/SA 11.89-110 mph
  • F/SA 11.76-111 mph

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Moneymaker
Administrator

Posts: 21725
From: Lyons, IL, USA
Registered: May 99

posted 01-29-2003 02:57 PM     Click Here to See the Profile for Moneymaker   Click Here to Email Moneymaker     Edit/Delete Message   Reply w/Quote
Change the PV. The one you have may be bad.

------------------
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,&'03
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!"
www.moneymakerracing.com

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Fastymz
Moderator

Posts: 14201
From: Reno Nv USA MEM#1240
Registered: Apr 2001

posted 01-29-2003 03:18 PM     Click Here to See the Profile for Fastymz   Click Here to Email Fastymz     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Moneymaker:
Change the PV. The one you have may be bad.


Go with another 6.5 one or change it to a 4.5?
I have had few back fires thourgh the carb dont know why either?Only when trying to start it it seems if it does not start I get a puff of smoke out the air cleaner,that has happen about 5-6 time since I rebuilt the carb.

------------------
SCOOP
oddly obsessed with big scoops on little Mustangs

2.26 60'S
14.9 @ 90.86MPH

65 coupe,351w,C4,Big Boss 429 hood scoop,8"3.40 TracLoc,Cragar SS,Black Suede.

https://mustangsandmore.com/ubb/Fastymz.html

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SteveLaRiviere
Administrator

Posts: 37258
From: Saco, Maine
Registered: May 99

posted 01-29-2003 03:26 PM     Click Here to See the Profile for SteveLaRiviere   Click Here to Email SteveLaRiviere     Edit/Delete Message   Reply w/Quote
You're running it without a choke, right?

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

Please remember our sponsors,
Mustangs Plus, NPD, Osborn Reproductions, MyFordPerformance.com, and FordRamAir.com

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Moneymaker
Administrator

Posts: 21725
From: Lyons, IL, USA
Registered: May 99

posted 01-29-2003 03:52 PM     Click Here to See the Profile for Moneymaker   Click Here to Email Moneymaker     Edit/Delete Message   Reply w/Quote
Do you have one on hand? Any size? Just for a test.
If the car back fired then you probably blew out the PV. If you have to go and buy one from Summit then get a 4.5.

------------------
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,&'03
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!"
www.moneymakerracing.com

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Fastymz
Moderator

Posts: 14201
From: Reno Nv USA MEM#1240
Registered: Apr 2001

posted 01-29-2003 07:05 PM     Click Here to See the Profile for Fastymz   Click Here to Email Fastymz     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by SteveLaRiviere:
You're running it without a choke, right?


Yes no choke or choke plate at all.

Alex I have to buy one anyways,so I'll pick up both a 4.5 and a 6.5.
I have the car apart right now so when I can try it.I'll let you all know what happens.
But it only does it once in awhile.


------------------
SCOOP
oddly obsessed with big scoops on little Mustangs

2.26 60'S
14.9 @ 90.86MPH

65 coupe,351w,C4,Big Boss 429 hood scoop,8"3.40 TracLoc,Cragar SS,Black Suede.

https://mustangsandmore.com/ubb/Fastymz.html

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