question on jet sizes
 

I have a 1972 newport i just got done doing a sleeper project on it i guess you could say. It has a 440 with an aluminum intake comp cam in it i cant remember the exact numbers but i think it was .488 and something else. hooker super comp header 3 inch dual exhaust and a 4 speed if that matters for my question. The carb is my problem! I'm dieing to drive this car everywhere! Someone put 75 primary jets in it and 78 secondaries and it was studdering i guess you could say above 3 grand it operated like a dog even revving it in neutral. So i did research found a couple guys say 70-72 on the primaries and nothing on the secondaries(as in i found no info). factory says 70 primary 75 secondary. My plugs with the 75 and 78 jets were rich and not brown it just wasnt right! Anyways after swapping the jets to 72 and 75 this thing drives way better im very impressed with the difference. But another thread i found the guy has a very similar engine build to mine he says a mild cam i would call my cam mild? anyways he has 71 primary and 69 secondaries. So am i way too big on my secondaries still? im very curious to hear what other people are running for jets or even teach me how to figure out this whole jet size deal. How do you determine to go smaller or larger? simply check the plugs? Out of all this typing i think i failed to mention my carb is a 770 holley street avenger. also if it matters its just timed to 12 degrees BTDC as of now. Ill do the whole 3 grand and 38 degrees after i break this engine in more. it has maybe 10 miles on it now but a decent amount of idle and staring time. thanks for the help!

There will be a few posts here I'm sure!

For me I did what you are doing now and that is asking.... After that I found for me, because I'm still learning the holley, it's trial and error. I keep track of every change I make in a notebook and only will make one change at a time so I can truly see or not see the difference. Redundant and slow but works for me at this point. Hopefully in the future when I'm better at these things, I won't need to do all that but I doubt it.

Also, other things to think about...the other pieces to the holley puzzle... Accelerator cams and what they do..jets(as you've mentioned) power valves, squirters, vacuum secondary springs if applicable, accelerator pumps themselves.. Plus more, curb idle, air idle etc.. And yes of course probably most important, timing!

That's what I know to help.. Not much, I wish it I was more but I'm sure others will help out more.. Good luck.

WHERE IS THE TIMING?????

That is the numbaw wha-HAN question.

I don't just mean INITIAL. I mean what is the initial, how do you know the balancer / timing marks are correct, have you played with it, and how did you DETERMINE that "12" is correct? WHAT is the timing curve? What is the total advance, and at what RPM? Has the distributor been re-worked?

AFTER you get the TIMING beaten into shape, THEN worry about the carb

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You have not said ONE WORD about the POWER VALVE

What are the cam specs? Where is it degree'd?

What is idle manifold vacuum?

What do the plugs look like?

Consider SERIOUSLY buying yourself a wideband O2 setup

Timing is set 12 degrees BTDC that's it for now like I stated in my post. I'll work on setting the total to 38 degrees at 3 thousand rpms today. How do I know what the timing curve is? I sure hope 440 source can accurately put numbers on my harmonic balancer.... I tested that idea before installing the engine to make sure the numbers are correct. The distributor is aftermarket I don't know if it has been reworked I do have a timing curve kit for it though.

Hang on I'm going to look into this curve timing kit when I get home. I'll swap the springs to lighter ones so it engages quicker and play with it and let you know what I find out!

Should I go with two stage advance curves or single stage advance curves?

Ok I have it all timed. Initial is 12. 2500 rpm is 38 and 2500 with vacuum advance on is 50-55ish. I put the pink and grey spring in my distributor and it makes a huge difference. But it still feels like the carb might be out of wack. I'll go drive it around and check the plugs. See what I discover.