Holley jetting Question

[smokindodge]

So, I thought my tuning was pretty close, I drive the car mostly at 4700 -5000 feet, I just went on a trip to california were the elevation is 300-500 feet, I left the same jets in the carb, the car ran like a raped ape, long story long, if I was running say 75 jets at 300 feet what should I go down to at 4700 feet?

 

[yammerhammer]

"IF" it were me, I wouldn't change the jets... just yet. I would look to see
what power valve I was running. Most of your driveablility (running like a raped ape) would come from on/off throttle performance which comes from the power valve. Just like the needles in a sled or needles in a Q-Jet carb.

Obviously you are going to pull less vacum at a hight elevation therefor
opening the powervalve later and not adding the fuel it needs.

 

[dice]

"IF" it were me, I wouldn't change the jets... just yet. I would look to see
what power valve I was running. Most of your driveablility (running like a raped ape) would come from on/off throttle performance which comes from the power valve. Just like the needles in a sled or needles in a Q-Jet carb.

Obviously you are going to pull less vacum at a hight elevation therefor
opening the powervalve later and not adding the fuel it needs.

I would be looking at the plugs also, should have been scary white at sea level.

 

[smokindodge]

I pulled a plug last night, blacker than....heck! hmmmm, I guess I will just drop a couple sizes and see waht happens

 

[yammerhammer]

Most likely your power valve. I would check THAT before you
change the jets.


You probably already know this but... Put a vacuum gauge on your vacuum port and record how much vacuum it pulls at idle. Slap in a PV that’s about 2" below that number. If you go to low it'll stumble at the hit of the throttle, if you go too high, it'll dump to much fuel and make it rich. Be sure and set the mixture screws first. Once you do that, then you can check/change check the jets.

 

[Gimpster]

Like Yammer is stressing.... The power valve is too fat

Been so long since I ran the Holleys on my dirt oval cars that I can't remember the numbers.
Maybe do some digging around in search engines for some of these dirt tracking or drag racing guys and what they are twisting into their carbs.

----- Gimpster -----

 

[smokindodge]

K, it idles around 8-9ish, I have a 6.5 PV in the primaries with 74 main and a blocker in the back with 84 main, this was the setup I ran on a race motor that ran 8500 RPM, in thinking about it, what i am running is a little more cubes, but alot lower RPM, like a max of 6000, smaller cam, less compression, down from a 6 inch rod to a 5.7....I went down to a 68 in the primaries and a 74 in the seconday. See what happens....