[gordon norris]

Hey i have 66 mustang and i know nothing about tuning carbs here is the problem if i press on the gas hard then let off of it it stalls and dies. Smells to me that it is running a little to rich could it be loading up. If so how do i adjust it. What could be the problems any help would be great. Info on motor i think its a 289 rebuilt not sure what cam but does have 4 barrel holley on it can take pic if need to see what kind or carb

[speedfreak]

You will need to change your jet size to limit the gas flowing into the motor. Holley can be a little difficult to tune but they are one of the best to use.

[69fastback]

What size carb? Holleys are by far the easiest carbs to tune. You shouldn't need any bigger than a 600 cfm on a 289.

[460brevill]

sounds like the power valve diaphram is bad.

[speedfreak]

Originally Posted by 69fastback What size carb? Holleys are by far the easiest carbs to tune. You shouldn't need any bigger than a 600 cfm on a 289.

I have used a 750 Holley with a 289 without any trouble. I do not believe that is the problem unless it is a rediculously big carb, like an 850 or something. It should be a combination of jets and squirters, or the ventris, that is causing the to bog when he lets off the gas

[speedfreak]

Originally Posted by 460brevill sounds like the power valve diaphram is bad.

If it is the power valve there would be some back firing and it would not run well being that the power valve would hinder the entire performance of the vehicle not just a bog when you let off the gas. He may also need to look at his pump cams on the carb as well as the jets and ventris, or squirters.

[460brevill]

it isnt bogging it is shutting off and running rich.still sounds like valve.

[gordon norris]

so sounds to me there is no quick fix i would need to replace the carb or rebuilt it

[BA Mustang]

Just sounds like the carb is running rich and the mixture screw needs to be turned in.

[69fastback]

Originally Posted by speedfreak I have used a 750 Holley with a 289 without any trouble. I do not believe that is the problem unless it is a rediculously big carb, like an 850 or something. It should be a combination of jets and squirters, or the ventris, that is causing the to bog when he lets off the gas

A 750 out of the box is good for the 500 hp mark, which is way overkill. Anything more than a 600 is too much for a stock 289.

Originally Posted by BA Mustang Just sounds like the carb is running rich and the mixture screw needs to be turned in.

A big misconception about carbs, is that the small screws on either side are "mixture screws," when they are actually idle air controls. The correct way to adjust the mixture is to re-jet the carb.

[gordon norris]

so whats the best way to know what jets i need is there a number on the ones that in there or a way to tell if they are diffrent

[bossman69]

My car has a 2bbl 500cfm racing carb and it had set up for at least 2yrs before i put it on but I adjusted it by listening to it.I dont have a timing light or a tach but i think I got it pretty dam close cause i can hit tha throtle on tha carb and let go and it wont bogg down or die. Onlt thing I think you should do is if you have a tach then set it at the proper RPMs and adjust the air fuel mixture. It shouldnt be that dam hard but just depends on tha carb.

[69fastback]

A timing light has absolutely nothing to do with the carb. Jetting it takes a little practice, but isn't hard.

[bossman69]

But if the timing is just slightly off wouldnt adjusting the carb be a little bit difficult?Only reason im asking is cause Im not sure if my cars timing is set right and Ive adjusted the carb and it seems to be ok.

[speedfreak]

Is the carb a double pumper or a quad, because if it is you need to check the jets on the secondaries by the sound of what is happening. You need to check the size and then go down a size or two at a time. It will be trial and error until it is tuned correctly to your needs.

[speedfreak]

Originally Posted by bossman69 But if the timing is just slightly off wouldnt adjusting the carb be a little bit difficult?Only reason im asking is cause Im not sure if my cars timing is set right and Ive adjusted the carb and it seems to be ok.

The only problem timing may have is back firing or an idle adjustment. I run mine a little retarded. But your carb will use the same amount of gas at a specific rpm no matter what the timing is.

[bossman69]

From were it is right now im happy but I thought my motor had a mild cam and it doesnt sound anything like it.No lope. Its smooth.