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Discussion Starter · #1 ·
(NOTE: This is my second time typing this because right when I finished typing it the first time my damn web browser bit it, so I am unhappy about that, but I will do my best to include everything I wrote in the first version)

My mustang has this annoying stumble that has creeped up a little while ago. Here is the deal.

- It only does it under 2000rpm, never after.
- It doesn't matter what gear I am in, but the harder I press the gas the worse it sputters and jerks
- It doesn't do it all the time, only sometimes
- It feels like spark cutting out sparatically
- It only does it when warmed up, it runs fine cold

It is a 69 351w with an edelbrock carb and a pertronix. I changed the coil thinking it was that acting up, but it didn't help. Could it be the cap and rotor (they are old)? What about the pertronix? The kicker is that it is heat related, and yet it still isn't consistent all of the time. It seems and feels electrical to me, but what else could it be? The engine has a vacuum temperature switch that switches from manifold vacuum to ported vacuum as it heats up, could something be funky in the switch or the sources of vacuum? There are no vacuum leaks either.

Help this poor, troubled young VMFer out /forums/images/icons/frown.gif
 

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Well, I know mine did that prior to me swapping out the plug wires. Stumbled like a drunken prom date at low rpms. I slapped on some new wires and it runs great. Turned out that aside from the obvious one burned out wire, at least 3 other wires were going bad too. Found that out at around sunset when it was just getting dark and I saw little sparks from the different wires.

Hopefully your problem is as simple as mine was. Good luck.
 

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Discussion Starter · #3 ·
I thought it could be the wires too. Last night I started it up and looked around and saw nothing flashing in the night. Maybe one of the wires is burning up. I will have to order up some new wires, and probably a cap and rotor too, it needs them anyway.

But still, why would it do it every so often and only after it warms up?
 

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I would check the mechanical advance weights in the distributor and make sure they are lubed and free. They could be rusty or binding when evrything warms up, then releasing and advancing your timing when the RPMs get high enough.
 

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Chunkie in the carb intermediate circuit? This circuit is primary source of emulsified fuel under part throttle in the lower rpm ranges, at least on Holleys and 4100's...

The reason I mention it is because it happened to me on the D-coder a few times over the years.

You guys are probably right about looking at ignition but I thought I'd offer an alternative view..*G*
 

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I use a timing light to check for bad wires, testing each with the light as I rev the motor. Any inconsistancy in the strobe of the light means a bad wire.
 

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Dave:

Other than the smart ass suggestion of keeping the revs above 2000 at all times, I agree with the other posts, it's either ignition or fuel related. Fix the obvious stuff (Cap & rotor), check that all electrical connections are clean and tight (including the solenoid, the ignition switch and the coil) and make sure that the carb doesn't have gunk floating around in the float bowls that are plugging up the jets etc. After that, I agree that the vacuum temp switch deserves a close look. Can you bypass it and run without it for a while? If not, the factory service manual for that engine might be of some help. Good luck.
 

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Discussion Starter · #8 ·
I have driven it from work just now, and it seems to be doing this wonderful stumble and miss both cold and warmed up now. It even backfired through the carb while I was driving up a hill in 4th gear! It has never done that, ever. I will try running it by bypassing my vacuum advance and see if that does anything. And I will check all the wires later tonight too. I wish I could get it running good again, I miss having it purrrr....
 

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Discussion Starter · #9 ·
Chunkie in the carb intermediate circuit?

Isn't he that guy with the one eye from Goonies?

A week or so ago I pulled the top of the carb off to check for "Chunkie", and it was sparkling clean in the bowl areas. I sprayed carb junk in all the open holes I could find to clean them all out, or to free "Chunkie". Put it all back together and it was the same, no change.
 

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Discussion Starter · #10 ·
I just did that a week ago. I took everything out of the distributor and cleaned and lubed it accordingly. Still no change.

Atleast by the time I am done trying to track the problem down everything else should be in excellent working condition /forums/images/icons/smile.gif
 

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it was sparkling clean in the bowl areas. I sprayed carb junk in all the open holes I could find to clean them all out, or to free "Chunkie".

hehehe....what a wordsmith...

The intermidiate circuit is buried deep in the bowells of the carb (at least on Holleys) and often superficial spraying of orifices doesn't help. How's that for a witty yet cogent response?? *G*

I don't know enough about Edelbrocks to speak with authority on this subject so I'll have to leave it the Carter/Edelbrock gurus.

As to ignition causes,let me re-read the thread, do some cogitating, and get back to you...
 

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I'm taking a SWAG (scientific wild a** guess), but my problem was engine heat. When the engine was cold, I could only see a spark on my burnt out #4 wire, but as the engine warmed up, I guess the boots expanded from the heat from the headers enough that the other sparks showed. Keep in mind that the rubber on the old boots was no longer pliant so instead of expanding and closing up the cracks, it actually opened them up like a cracked sidewalk.

That sort of explained my light show. I still haven't figured out why it would stumble at idle and not at higher revs, although at speed, I would get an occasional misfire every now and then. Either way, new wires solved my problem. I'd definitely go with the other guys' advice and start with the simple things like cap, rotor, and wires then move on to the carb and vacuum.
 

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Edelbrock carbs are tuned with the metering rods/jets and springs. I had to buy the tuning kit to get rid of the stumble in my carb. If you look at the manual ( or go to their website) you can change metering rods to richen the bottom end of the carb circuit. A lot of times the low rpm response is too lean, mine was. I disconnected that temp. sensor on my '69 351W and went to straight vac. advance.
 

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Such a preturnatural riposte from a machinist

That's what 12 years of Catholic school with randy brothers will do to ya..*G*

I'm not a bad fencer either, preferably of the wooden kind...

heheh
 
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