Sputtering and Stumbling under accel

jnobles06

Member

Oct 23, 2003

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6

Clovis,NM

Jul 28, 2007

#1

• Jul 28, 2007

• #1

i know this is a classic tech but i have a 95 mustang with a 74 351w that is fully built and stroked with h/c/i. i am running a holley 750 with a summit electric fuel pump and a holley reg. @ 7psi w/ full msd ignition. the car was just taken for its first drive and as soon as i give it a little gas the motor sputters until i give it more gas and gets past about 2k rpm. then it runs fine. this is my first carbed motor so im kinda new to this any one have any idea what the problem is? any input would be greatly appreciated. thanks.

 

D

D.Hearne

New Member

Sep 29, 2000

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south louisiana

Jul 28, 2007

#2

• Jul 28, 2007

• #2

With the engine killed, remove the air cleaner assembly. As you look down into the throttle bores, move the accellerator linkage and see if it moves any distance till the accellerator pump shoots fuel out of the squirters. There should be no slack between the accellerator pump arm and pump lever. As soon as the throttle moves, fuel should shoot from the squirters into the bores. Ignition timing should also be advanced to about 10-14 degrees BTDC at idle. Check these two things and see if that helps. If not, there can be other things that'll do it as well.

 

jnobles06

Member

Oct 23, 2003

85

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6

Clovis,NM

Jul 28, 2007

#3

• Jul 28, 2007

• #3

ok i advanced the timing from 6 to 12 degrees with the timing light and checked the carb to see if it was squirting and it was good then i gave it a little gas and it stumbled then the idle increased to 1600 from about 1000 rpms.

 

jnobles06

Member

Oct 23, 2003

85

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6

Clovis,NM

Jul 29, 2007

#4

• Jul 29, 2007

• #4

well i pulled out my spark plugs and they were black i think im running to rich or something i checked the float level on the carb and it was ok do you think it could be the spark gap or the crappy autolite plugs i was running?

 

N

NewStangOwnr

New Member

Aug 10, 2006

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Jul 29, 2007

#5

• Jul 29, 2007

• #5

If you stumbling under acceleration than you most likely are running lean.

Same thing happened to me, stumbling in low speed good in higher speed. Changed to 1 stage rich on the carb and now it goes fast.

 

D

D.Hearne

New Member

Sep 29, 2000

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south louisiana

Jul 29, 2007

#6

• Jul 29, 2007

• #6

Crappy Autolite plugs ? These are all I run. Nothing crappy about em. It's probably the crappy MSD ignition. causing the problem. Or crappy gas with water in it.

 

ratio411

Founding Member

Apr 21, 2002

3,870

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109

Pensacola FL

Jul 29, 2007

#7

• Jul 29, 2007

• #7

Unstable idle that you described is often a vac leak.

Do some reading on the Holley carb so you know how to tune it.
It is really simple, but if you don't know what does what, it will drive you up a wall.

Stumble while the throttle is in motion is usually the accel pump circuit.
Stumble on steady cruise or very light throttle changes are usually jets.
Black plugs are too much fuel.
White plugs are too little fuel.

Time the engine, then set the idle speed, then set the idle mix, then reset the idle speed, then set the accel pump.
If you do it in a different order, things will be out of whack.
To set the accel pump, then set the idle, will make your accel pump clearance different than before you set the idle... for example.

Also, check your squirter size... try sizes between 28 and 35, but only after your accel pump linkage is dead on.

Also, if you have a radical cam, you may need to swap power valve 'size'.

 

ratio411

Founding Member

Apr 21, 2002

3,870

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109

Pensacola FL

Jul 29, 2007

#8

• Jul 29, 2007

• #8

jnobles06 said:

checked the carb to see if it was squirting and it was good...

Click to expand...

We are not concerned that it isn't squirting fuel.
We are concerned if it dribbles fuel when the throttle linkage is moved in the slightest.
If fuel is not supplied to the engine the instant the throttle is opened, you will have a big hole in throttle response.

So, without engine running, does the slightest motion or wiggle of the throttle produce signs of fuel from the squirter?
Is the pump shot from the squirter instant, or does the throttle open some before the fuel starts?

 

jnobles06

Member

Oct 23, 2003

85

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6

Clovis,NM

Jul 29, 2007

#9

• Jul 29, 2007

• #9

my carb is squirting with the car off when i move the throttle very little. the reason i called the autolite crap is because im supposed to be using accel 276 because i have world products windsor sr heads my compression is 10.5:1 i think they have a longer reach and they are tapered. i just went to autozone and they didnt have them but they said the autolite would fit in the heads but i dont think the reach is the same and i dont think they are tapered. i am also cammed with a lunati cam with the same specs as the edelbrock torker cam.

 

D

D.Hearne

New Member

Sep 29, 2000

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south louisiana

Jul 29, 2007

#10

• Jul 29, 2007

• #10

I just replaced the crappy Autolite plugs in my 3 year old Canfield heads today. It was time for them to be replaced after three years. They were nicely carboned up after that length of time. The fresh ones (Autolites too) are great, the 331 starts sooooo much easier and runs smoother now. Did a nice burnout in the driveway after the plug change. These are 5/8" thread and 3/4" reach with a gasket ring. Autolite Part number 3924. I just hate it when someone clearly states he knows nothing about his carb problem, then blames the parts used before he even figures out the fix. Your problem can be either a carb or ignition problem. We'll do all we can to help, but please don't start with blaming parts that others have used without problems for years.

 

Iamdiffrnt

Member

Nov 13, 2005

197

6

19

South of Detroit, MI

Jul 30, 2007

#11

• Jul 30, 2007

• #11

My cousin (die hard Chevy man) wouldn't use anything but Autolite plugs.
They were the only plugs that held up for any length of time on his engines.

 

jnobles06

Member

Oct 23, 2003

85

0

6

Clovis,NM

Jul 30, 2007

#12

• Jul 30, 2007

• #12

my spark plugs are black with carbon i believe that they are the problem because they dont burn the fuel efficiently enough for the high compression that i have and maybe i need a copper race plug that is more suited for my application. so i do have a reason for blaming them. any suggestions?

 

D

D.Hearne

New Member

Sep 29, 2000

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south louisiana

Jul 30, 2007

#13

• Jul 30, 2007

• #13

Yea, replace em with fresh Autolites. The difference between the old and new ones in my 331 was like night and day.