I Thought I Knew How......

horseballz

10 Year Member
Sep 30, 2009
824
20
49
Las Vegas, NV
Hey Folks,

Long time no post because I've simply been driving my car! Now I need some help.

I'm 66 years old, been driving carbureted vehicles all my life and I thought I knew how to properly tune them. It turns out that I'm absolutely and completely wrong! All else seems great, but I cannot eliminate an annoying hiccup/burp/hesitation off of idle and/or light cruise! Here's details of the scenario in my '68 Mustang Coupe:
> 2000 5.0 crate motor with GT40 "P" heads and stock late '90s Explorer cam, installed 4 degrees (IIRC) advanced, standard 1.6:1 roller rocker arms/T5 transmission/3.80 rear gears
> Edelbrock Performer RPM intake.
> Quick Fuel HR-580VS, vacuum secondaries (Holley 4150-ish, but with 4 corner mixture screws and changeable air bleeds)
> Mallory Magnetic Breakerless, vacuum advance distributor
> Tri-Y headers/2 1/2" Magnaflow exhaust
I have all available accelerator pump cams, a wide selection of air bleeds, idle restrictors, jets, power valves etc. I've played around with many combinations, some were horrendous and a couple others came "close but no ceegar!" Except for this hesitation issue, this 2700 lb coupe is pretty stout and runs fantastic in all other ways. The hesitation/burp, along with having uselessly tried every trick I know, is driving me nuckin' futs!
mad.png


Scratchin' My Head?
Gene
 
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I think I already did that? I guess I need to look/see. This annoyance has always been there though! Thanks for the thought and nice to see you're still around and kickin' as well as still covertin' them there fastback thingies!
Thanks Again,
Gene
 
Todays fuel is not made to be run in carburetors
You are experiencing why
You can switch from spark port to manifold or most likely visa versa for your vacuum advance supply
That Mallory still has what would be called a breaker plate
Make sure it is tight and check your rate of timing advance
I want my advance all in quick but I am at 5000 feet elevation
I have mine all in by 3200 or so and it is above 40 degrees
I also run a mix of racing fuel
10 to 15 percent or so of 130 Sunoco leaded
A fuel mix like that alone will most likely solve your issue
 
You've got a few years on me horseballs
I am sure you know what you are doing
Two heads are better than one and several are even better
Make it fatter
If you are pinching on fuel the symptom will be the same
Raise the float level in that Holley a bit
Like the 4 mixture screws
I agree with horse sense to get a big squirt going
I have a 50cc on my Holley 780 and run the red pump cam set to right now
 
So it’s a throttle tip in hesitation? I am betting it is an ignition timing thing. The mechanical or vac advance are my suspects. If your accelerator pump is good, you are probably chasing the wrong part of the fuel/air/spark formula.