Why is my engine sluggish? Any thoughts on Holley vs. Autolite 4100?

natejones75

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Oct 21, 2003
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My '65 GT Mustang Fastback only has about 6,000 miles since its rebuild 5 years ago. The motor just doesn;t seem like it has as much power or snap as it should. I am look for advice to correct that. Here are a couple of possibilities...
1) Instead of the original autolite 4100, it has a Holley 600 on it, which I am leary of. Sometimes when you punch the pedal down, it just kind of coughs or it even dies. I want it to snap and burn the tires. what are your thoughts on the autolite 4100 vs. the Holley? If this is the problem, wht cna I do to fix this carb?
2) the distributor is not as great as it should be. You can feel some side play of the shaft in the housing. I have put on a petronix ignitor, but I did not get that much improvement over the points.
I am looking for any advice here to my my fastback scream, while keeping the original 289 4V. Any advice? [email protected]
 
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sixtyfive

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Jan 9, 2004
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i have a holley 650 on mine and it runs perfect

i know what you are talking about cause my quadrajet on my 305 is doing the same **** bogging out, it needs rebuilt i know that, but how old is your holley?
 

Snail50

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Mar 24, 2001
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My 289 2V is kind of a dog, too. It goes, but there's no "snap," like you're saying, and sometimes it will stumble when I start to accelerate. I'm interested in hearing what everyone has to say on this. I checked my plugs, cap, and rotor, and they all look fine. The fuel filter looks clean and new, too.
 

stang-69

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Jun 5, 2003
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Hi!
I´m not a carb-guru, but still, I think it would be a good idea if you told us what kind of secondaries you have, vacuum or mechanical, and what engines are you talking about, 289, 302, 351 .... I believe that with that information it would be easier to give some advice.
If, for example you have a double pumper, one idea is to check the secondary jets ... or the cam timing.

A 600 cfm Holley on a 351 can be a bit to tiny, if you are running a 302 it´s Ok and so on ...
 

rebel65

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Feb 1, 2004
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if it is a double pumper...there you go, but if it is say a vac secondary then i would be very surprised. i have a Holley 670 Vac secondary and it definatly snaps and burns on a good pump. your dizzy scares me if it moves side to side..i would say get a good HEI or tighten it down...or something...
 

slapper

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Mar 6, 2002
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Check to see if the acccelerator pump is providing a FULL shot of fuel into the front venturis when you move the gas pedal. Slowly moved? Moderately moved? Quickley moved? If not, you are leaning out upon throttle application, and the cough/die is a result.
The 4100 Autolite is an awesome carb. The large boost venturis provide a great signal with plenty of snap.
The Holley is also a great carb, with almost endless tuning abilities.
Check the accelerator pump shot first, and also for any possible vacuum leaks, and post again.
 

302 coupe

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Mar 2, 2000
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you might as well try and tune the holley to work better. But.....the 4100 is the best 480 or 600 cfm carb around. They are simple, reliable, adequately sized, and very easy to tune. If you already have a good 4100, swap it on and see what happens. Holleys are good, but can be a real pain sometimes. Get that distributor taken care of too, a loose shaft can make for erratic timing.
 

Max Power

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Jul 31, 2003
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If the fuel in your area has alcohol based additives, that can eat away at the accelerator pump check valve, rendering your pump useless. That will cause a bog. I would buy a kit for the holley, rebuild it, and see if it performs better.