carb question

[Mike Smoker]

Struggling with carburetors. I took a Holley 570 with vacuum secondaries off of my car because of the stumble when starting to go. When the secondaries opened, the car ran great. I put a 600 double pump with mechanical secondaries, and mechanical choke on. After adjusting the idle mixture screws, the car runs good from idle to going pretty good. When the secondaries open, the motor is flat and won't pull very hard. I took the carb apart to check jets, 66 primary and 73 secondary. Also, one of the secondary jets wasn't tight. I checked float level before removing carb, that was fine. My question is, is that a standard separation for jets? The carb was new from Auto Zone. If I am going to change jets , what would be a good number to start with? The plugs are a dark brown color. Any help would be appreciated. Mike

[Bob Taylor]

what jets were in the 570 ? Lean is lite grey white is extreme , black is rich . Anyone want to comment on brown? Thats the extent of my carb knowledge anyone else ?? oh yeah besure with the engine off the secondaries are squrting fuel in , sometimes they gum up from the fuel Bob

[Greg_M]

Mike,
Ran a 570 for years and recently put the Holley #4776 600 DP on my 302 crate motor. Your DP has the correct stock jets. I had to reduce the secondaries from 73 to 70 to keep the WOT AFR above 12:1.

If I slam to WOT at a low rpm in a tall gear, is the only time I might get a 1/2 second stumble but after that hang on. I can slam it above 2500 and it's all go. I can roll into WOT at 1500 rpm in 5th with a 3.08 rear and she pulls withought complaint.

If your car feels flat and your plugs are dark brown, you might have the same problem I had; too rich on the secondaries. Mine went as low as 10:1 between 3000 and 5000 rpm at WOT. Changing to 70's took it to 12 - 12.8 AFR at WOT between 2500 and 6000.

TIMING, TIMING, it makes a huge difference in response. I run 14 base with 26 more all in by 2500 and 8 more vaccum above 10". If I back the base down to 10, she responds with hesitiation and stumbles. More than 16 and she bucks under light load and decelleration. I never hear any pre-ignition.

Plugs are a light tan insulator and dark gray threads with no soot coming off on my finger when I touch the threads.

HTH,
Greg


What are you engine specs?

[Todd Buttrick]

What engine and mods are you running?

[hind sight]

Mike post your engine specs.Cam,heads compression.timing,static and total,ect.
Also specs of carb noting squirter size. Accelerator cam color and accel pump size.
Start with basic float level to be sure it's at the bottom of sight glass along with fuel psi being sufficient.