Easiest thing for you to do is call Ruggles order his book, tell him your carb number, and he will sell you whatever jets, rods etc that you need for your build.
You may as well take advantage of his intricate knowledge, rather than reinventing the wheel.

 

That has to be the best long term plan. I've got to get the car home (350 mile trip back) and driving with detonation is NOT an option.

I might have to pick up a temporary carb (one that I can get parts for locally) to get it home, then back to tuning this one the right way.

 

I've checked what's in the carb now:

#79 primary jets (#77 was stock)
#52 primary rods
CH secondary rods

 

Do you have the "k" rods? Did you measure the power tips? My 17059211 Q-jet is stock with 77/53 jet/rod combo. It runs fine here in the sub 1000 foot elevations-not lean- even with true duals, an energizer cam and 34 degrees TOTAL advance. It never detonates. With more displacement you likely need richer(smaller) rods than mine to totally avoid a lean condition. If the rods are in that ballpark some of the other excellent suggestions should be checked. What is your Q-jet part number?? I'm no guru BTW. Good luck.

 

Oops--I forgot to insert "mechanical" in front of advance. I run 12 degree vacuum advance for total cruise of 46 degrees. I have thought about going with more vac advance but the mpg is 18-20 highway and it runs just fine now. Also, I now see you have a 17057204.

 

so .079-.052=.027
IIRC .035 was good for my motor.

Yes taper and spring need to work together with the vacuum you are
getting.

 

If it is detonating at cruise as opposed to acceleration, you may be able to switch to a colder plug to at least get home and go through the carb. I made a cam swap and noticed detonation at cruise. I could get the detonation to stop with just a touch of throttle. I switched to a colder plug and it went away. Eventually, I had a guy rejet the carb.

 

Subtraction is not a true measure. A 79/52 combo is not the same as a 75/48 combo since we are dealing with circular areas.

 

Agreed.
I did some area math and vac measurements and seat of pants
with an ear thrown in.

This was before the modern A/F equip avail to the hobbyist

I just wanted to add to the OPs info on what can be done.

Notice taper of rod and vac spring were mentioned.

but still there is a small diff in size of his jet and rod.
.027 is lean to me

 

The stock 77 qjets are extremely lean from the factory and bumping up to 79 jets etc just won't cut it with a beefed up 409 with headers etc.
You're going to have to so some drilling and rod changes and numerous other mods etc, etc to get it that carb right.

Best just to get home, is to retard timing a bit, try to keep the coolant temp down,(drive at night), keep the rpm down or perhaps find another used spreadbore temporarily from a bb.

 

Does your carb have the 1/8" airbleed in it just below the parting line between the top/main casting . If it does, Cliff (from Cliffs hiperformance ) told me that its near impossible to get a good fuel curve with this setup. I plugged mine, and resized it to .070" went to a 73/44 jet and rod combo and resized the idle tube and idle down channel restriction to .037"/.052" respectively. I also drilled out the idle mixture screw holes to .093". The little testing I did with it before I pulled the engine was spot on. Nice idle, crisp acceleration with smooth transition onto the secondarys, and good cruise characteristics, but no idea what the AFR or fuel mileage was.
Cliff told me that the idle circuit in the Qjet is very lean, and to get the carb to work properly at all levels the idle circuit must be fixed first....leave the secondarys alone for now.
Investing $20 on Cliffs book is really worth it if you want a good understanding of the Qjet. He has "Recipies" for carbs depending on the level of performance ......I went with #2

 

Thanks to your replies today guys, I haven't digested them in detail yet but I got it home today. Here's what I've been through so far, the saga continues.

I discovered that Don Mann at Mann Speed Specialty in Independence, MO really knows Q-jets. He founded that place back in the 50's and has been a die-hard Quadrajet racer in both oval track and drag racing for almost as long as the wheel has been around based on some of the stuff he showed me. If you have an opportunity to talk to him, just be respectful and treat him right, and he's a gold mine of information and friendly help.

He told me to pull the carburetor off and bring it in with me on Friday so I did. He "field stripped" it as I would call it like he has done to thousands of these things and replaced the needle & seat with a high flow one and put a set of #44 rods in it to get me home, set the float, checked the accelerator pump and reassembled it.

The thing that impressed me most was that he pulled original parts out of his stock, still in the GM Delco/Rochester packaging, that he guessed had been back there at least 20 years.

Anyway, I reinstalled the carburetor with a new fuel filter and checked a few more things. I fired it back up with a vacuum gauge and timing light and I'm getting 16-1/2" at idle, 10-11 at idle in park (speed was a little low at 575 RPM).

I also found that my vacuum advance was putting in 22 crank degrees advance. Ouch, with total mechanical at 36 degrees and vacuum putting in 22, that was a total of 58- far too much at cruise. I shopped everywhere local and could not find a Lars-recommended AR12 (VC1838) this morning, so I backed total mechanical timing off to 30 deg. so cruise would be a much more happy 50 degrees.

I also found a truck stop that had 100 octane race gas. This would take care of the facti I could not find better than 91 octane premium for the trip home.

Air/fuel ratios at cruise were still not fat enough. I was getting 15:1 on the wideband at cruise and when temps again crept up to 230 degrees I could hear more detonation if I tried to accelerate enough to feel it in the seat of the pants. Vacuum at cruise was 20". I think my radiator may be in marginal condition, so I'll replace it soon just in case just to make sure. However, no fuel will work right under lean conditions.

I'm going to work with O'Reilly's to get the right vacuum advance can ASAP and look into the mods described above. I can't solve the lean condition at wide-open throttle with (unmodified) jets and rods alone because I'm at the largest available jets and all (compatible) rods do indeed come with .029" tips. Now that I'm home, I have access to my Edelbrock kit with springs, etc. as well as the mods described above.

Much work to do...

 

From what tiny experimentation I've done so far, you must be right about the idle circuit. I can't get idle to go rich using the idle adjustment screws alone.

OK, I just ordered Cliff's book. I'm gonna need it to feel my way through this, I don't think the usual tuning steps (just jets & rods) are going to be enough.

 

Lars says the same thing about the Qjets. The idle circuits are notoriously lean. And because they feed off the primary circuit, you simply can't tune it 100% until you get the idle sorted out. I have the same problem with mine. I've dialed in as much fuel as I can into the idle, and it still stumbles at idle. It actually runs great once I put my foot into it though so I've just learned to live with it until I go with an FI setup.