OK, I'm not sure on your primary jets, but I'll guess that they are a bit too big.
Good numbers for the 390 with your build for a
starting point are going to be 52's or 54's for the primary, your plate is probably a 39, but let's leave that alone for now.
As Tristan points out, the PV is probably a 6.5. If you want to go with an 8.5 to try it out, that may work. I wouldn't. Go with a 10.5. Do not install a dual range PV. They are like 12.5 and another number like 9.5 ..something like that. They don't flow enough fuel and you definitely won't be happy with the price!
You need to buy some bits and pieces for this install. One is a quick change secondary spring kit. Your life will be much better. Believe me!
Next up, you need a secondary spring kit, and a pump cam kit. What will make your life much better, purchase a conversion secondary metering block so you can install jets instead of playing with secondary plates.
If your set on using plates, then take a look at an 18 or a 30. The 39 is god awful rich. The 32 or 4 is a possibility too if your secondary still runs rich. I doubt it will though. There is no rhyme or reason to the numbering for the plates.
As soon as you start building compression this all goes out the window.
Get yourself a vacuum gauge and hook into the base of the carburetor, not the number six runner. You won't get a good number there. I install a pipe plug in that tap, because it serves no useful purpose. Power brakes are for weenies.
Pump cams are going to be fun.
You are going to want a Pink or Orange pump cam. Try to stick with screw hole #1. Whenever you change pump cams, you have to check the gap at WOT to make sure you aren't going to tear the crud out of the pump diaphram. Don't skip this ever! Gasoline splashing everywhere is bad!
Your shooter will probably be a 28. Depending on how things are going in the engine, a 31 may help. With the 390 you don't need a 50cc shot. The 30cc pump that comes on it will be fine. Do not play with the black or Brown pump cams. If it's a 25, stick a 28 on there. I don't know what a 25 is good for, but it isn't for a car that gets stood on.
Tune the primary first. To start, set the
secondary idle screw to Holley's factory spec. It's in the manual. you may have to play with this if your idle adjustment screws don't do anything on the primary block. Bump the secondary plate open just a tiny, tiny bit if that's the case. That should allow you to shut the primary plates enough to close the transfer slots at idle.
Lock the secondary out so it won't pull in. The black spring will do that nicely. Your engine will not open the secondary against the black spring.
This is where an A/F meter will really help. You need to have a vacuum gauge to tell which circuit of the carburetor is running the show. If your lean at 15" HG, and rich at 10ish" HG, that's your power valve coming in.
You should idle in the 19"+ range in drive with your cam. Get it out on a cruise of 55 mph or so, look at your vacuum reading. Should be pretty high. 15+ inches of mercury. If you don't have an A/F gauge, go home and pull the plugs. It's hard to read plugs with reformulated gas, so just look for some color. If it's scary white, bump it up. If your running extended plugs, it'll be hard to do. Run conventional plugs for tuning. Then put NGK ZFR5N plugs in it. :grin:
A surge will indicate lean. Lean surge is found at cruise. You'll know it when you find it. If you can get rid of the surge by stepping on the throttle and getting into the power valve, that's what you have.
Get your primary jets straightened out, then put the purple spring in. Go out and stand in it. Look for people in official looking cars first! Purple will work with a basically stock set up long block and a few flow improving devices like your headers and intake.
Your vacuum is going to go to zip. Now your going to need an A/F gauge, or the folks at the strip timing you and lots of gaskets and jets. I recommend the A/F gauge.
Timing is going to play havok with you. Your going to need about 10 degrees of intitial, then you want 30-32 degrees total with mechanical all in. Try to find a 9R governor for your distributor. That makes 18 degrees of mechanical. Hopefully you made the trip to EI. The vacuum advance won't make much difference for your power circuits, but will pull in for cruise.
OK. That's enough for now. Enjoy the tuning experience!
CJ
