Author Topic: AF ratio when secondarys open  (Read 3445 times)

Offline MRSOFTE

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AF ratio when secondarys open
« on: December 21, 2016, 04:18:50 PM »
Good morning

Finally got too the point where I felt tuning my 7028210 by the seat of my pants was over. So I sprung for an AF gauge. So with 69 jets and 46rods and AX secondary rods on a K hanger. It idles at 13.7. heavy acceleration with out the secondary's is also mid 13's. Cruise is 14.6 to 51.1. I'm happy with that but maybe I could go a tiny bit leaner?
Anyway my question is....When the secondary's open it drops too 10.6- 11.1.     Is that good/normal???
Thank you!

Offline 77cruiser

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Re: AF ratio when secondarys open
« Reply #1 on: December 22, 2016, 03:09:19 AM »
If it goes back 12 -13 it's OK. If not you should lean it out.
Jim

Offline Frank400

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Re: AF ratio when secondarys open
« Reply #2 on: December 22, 2016, 03:12:45 PM »
When you say you could go a little leaner, do you mean at idle or cruise speed ?  Is that a stock motor or does it have a non factory camshaft ? 

   Assuming it's a pretty stock motor with plenty  of vacuum, I do run leaner than that at idle myself and also a bit leaner at cruise as well.  It's easier to changer the cruise AF with the later APT carbs like I run, but if I were you, here's what I would do, but that is just me.  I would slightly enlarge the upper idle air bleed which is most likely on the air horn on your carb.  That would lean out the idle and also have a small influence on the cruise AFR as well, but much more on the idle which I think you could lean out more. 

    Frank.

Offline von

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Re: AF ratio when secondarys open
« Reply #3 on: December 23, 2016, 01:39:30 AM »
I think he's mainly concerned with WOT with secondaries hooked up. Sounds like it needs to be leaned a little on the secondary side.

Offline MRSOFTE

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Re: AF ratio when secondarys open
« Reply #4 on: December 23, 2016, 03:26:59 PM »
Yes just WOT. Stock 396 and the Rochester has not been abused by a weird rebuild. The carb has the stock AX rods, I have two hangers a K and M the M is leaner that's the one I'm using. Adjusted the door tension until it bogged then tighten up a bit. Not sure what else too try?  :P

Offline von

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Re: AF ratio when secondarys open
« Reply #5 on: December 24, 2016, 02:16:27 AM »
AX rods are pretty rich at .0400. I'd try DA's which are .0443. If still too rich try something in the range of AU's which are .0530.

Offline 429bbf

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Re: AF ratio when secondarys open
« Reply #6 on: January 07, 2017, 03:42:18 PM »
question for the group some say 10 some 12 where are you getting these as good numbers . stop light to stoplight . 1/4 mile . i got 5   11 to 1 pistons and a bad block sitting here . but that was 2 0r 3 miles racing someone flat on the floor so the question is what would be a good number for that type of run?