Tuning Holley Carb

[66StangFastback]

Hey guys.

I have a 4bbl Holley carb, P/n- 0-80457S

I'm running really rich (I can occasionally get a whiff of gas while the engine is idling)

I was wondering how to properly tune the carburetor, so as to improve my gas mileage and have my engine run a little bit better. I have no accesory belts (no a/c, no p/s) and I'm getting in the neighborhood of 7mpg. I do play around a bit, but I still don't think my gas mileage should be that bad!

So I ask you all, oh mighty stangnetters, how do I tune my carb? My instructions say to turn the idle adjustment screws until it runs "right", but I don't know what "right" is...Are there any tools I might need to do this? I thought I read somewhere that you need a vacuum reader that you hook to a port on the carb, then turn the screws until you get the highest pull? Is this true?

Thanks for the help all.

 

[66StangFastback]

Update: If it gives any of you an idea of how rich I am running, I just pulled the #1cylinder spark plug and it was completely blackened and covered in ash.

 

[John Z]

Sounds like you have a real problem. 7 mpg? How heavy is your right foot?

A couple of web pages for ya:
http://www.fordmuscle.com/archives/1999/12/holley/index2.shtml

And straight form the horses mouth:
http://www.holley.com/data/Products/Technical/199R7948-5.pdf

Hope this helps.

 

[Max Power]

Sounds like you might have a blown power valve. I would replace the power valve and gaskets, adjust the float to just under the inspection holes, and start with the idle adjustment screws 1 and 1/2 turns from seated.

 

[thehueypilot]

What cfm is the carb? What is you engine size? Does it start quick and idle smooth? Need more info...

 

[19stang66]

the carb is a vacuum secondary 600 cfm. thats what mine is and i have the same one

 

[thehueypilot]

Need more info like.....what size jets front and rear? Power valve size? Sec. Vac. spring color? How many turns out is you air/fuel screw? What size engine and what is you vac. at idle?

 

[66StangFastback]

Sorry guys, as for the questions asked,

I do have a pretty heavy right foot, I'm a teenager and like to play around..

19Stang66 is right, its a vac secondary 600cfm holley.

Engine is a 289 with worked heads (angle job, chevy valves, etc.)

Haven't messed with adjusting the floats yet. Didn't buy the carb new, its been rebuilt.

Air/fuel is about 3/4 turns out from all the way, thats where we got the highest vacuum reading, which is about 15 Hg at idle

It does start fairly quick, and does idle smooth once it's running,

The jetting in the front is 66, don't know the rear jetting..

Not sure what the spring color is,

Carb was rebuilt less than 5000 miles ago so it shouldn't have a blown power valve...though what is it?

Thanks for the help guys, hope this bit of info helps a little more, and if you have any more questions that'll help out ask.

 

[D.Hearne]

How do you have the rest of the motor tuned ? Timing's set at what ? You have the valves set correctly ? There's no jets on the secondary side of that carb, only a metering plate. That's not likely your trouble. The secondary float may need adjusting (lower) Do you have a fuel pressure regulator inline before the carb ? Fuel filter ? Points or electronic ignition ?