hey, new to this forum, not sure if this is the right place to post this question....

1980 mild 350 chevy sb, i'm not totally sure about the internals of this engine except that it has a mild cam, some type of stock gm iron heads and somewhere between 9.5-10:1 ??

my holley 4150 650 has 68p/70s and the plugs look great, but i rarly open up the secondaries. I have read about holley DPs haveing the secondaries 5-10 jet sizes larger than the primaries. I was wondering if anyone thinks my 70s are too lean for the secondaries. It does sound lean after about 1/2 throttle. It sits on top of a performer right now, but I'm switching to either an X-celerator or a Torker II this winter.  

Whenever changing the jets, it's always safer to jet it up first, rather than down. So to answer your question, go ahead and throw some jets in the rear, and take it out for a spin. If it responds well, you can keep adding jet to it until it lays down, then pull it back out.

Check your plugs after your test drive, and if they look black, you know you've gone too rich.

Generally, the primary side of a double pumper will have a power valve, which opens up at low vacuum (near full throttle), and is equivalent to 6 - 8 jet sizes. I would not add any more jet to the primary side because you are already a few jets larger than the rear when the power valve opens.

Nevertheless, some double pumpers also have a power valve on the secondary side, so check for this before you do any jet change.

I think your first move would be to add 3 or 4 jet sizes to the rear and see if you can feel a difference one way or the another.  

Best place is at the track. Use MPH to determine if your going in the right direction. If MPH goes down, your going the wrong way. NEVER use ET to tune. I purchased an Innovate. A wide band O2 sensor. Works great.