Thread: 78 Trans Am getting some love

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Here's a carb tuning log to help you keep track;

To help you, I need to know the jets and rods you have installed.

Originally Posted by 36 sedan

To help you, I need to know the jets and rods you have installed.

My Sunday afternoon snooze got a little long

From the factory it has 56/40 primary needles in it, then I installed 58/44's in. I have some 54/38's that I did not try but they have a smaller diameter which would be going the wrong direction in my mind. So now I have 58/44 primary needles.

Factory primary jets are 89 with 91 and 87 in my kit, I installed the 87

Factory secondary is 86 with 88 and 84 in the kit, I installed 84

I still have the factory 6" hg step up spring in it.

These are the jets available in the 625 cfm kit which will fit in my 750

Primary main jet assorment of .074, .076, .080 and .082
Secondary main jet assortment of .078 and .082
Metring rod assortment of .056/.048, .058/.050, .058/.052, .060/.050, .062/.054 and .064/.056
Step-Up spring assortment of orange, blue, yellow and silver springs

I’m changing oil, plugs, wires, cap and rotor on mine today. In the morning I’ll finish with cleaning the air bleeds and changing the coolant, then out I go! Lol!!!

I hope your cruising went better than mine, mine lasted about 12 miles and my fuel pump croaked. The pump lasted only 8,100 miles , I think I'll get a used one from the salvage yard, I'm sick of new junk.

Dang it! Sorry for ya. I've spent my share of time hooked to a tow, I understand.
Even the old mechanical pumps have their problems (probably due to todays fuel additives). After the 3rd one went out on mine (what a bugger to change, had to pull the inner fender out to get to it), I converted to electric and never looked back.

My cruise got diverted by a honey do list, LOL! I'll have to wait til tomorrow...

STREET DEMON FACTORY SPECS;

750 stock jets = primary #89, secondary #86
750 stock rods = 56/40

You installed;

jets = primary #87 (2 steps leaner), secondary #84 (2 steps leaner)
rods = 58/44 (1-1/2 step leaner)
AFR @ idle = 12, AFR @ cruise = 12, AFR @ WOT = 10-11.5

You’re going in the right direction, stay on the primary and rods, should be able to dial it in with them. Change the rods to a 60/50 that will lean the cruise 1 step and lean WOT 3 steps, see what that does. May have to drop primary jets to #82 and rods back to 56/40 rods, to get the cruise. Then if the WOT is still rich 56/48 rods.

To lean = smaller jets and/or larger rods
To richen = larger jets and/or smaller rods

NOTE;

1 - jet size change (.003) with no rod change = 2 steps >/< (richer/leaner)
1 - rod size change (.002) with no jet change = 1 steps >/< (richer/leaner)

1,200 feet elevation is one of the reasons it's running rich. Hang in there, you're almost there.

Watch the timing for detonation at WOT, 39° is pushing it and may actually lose power.

I did notice that it lost some pull at that point,no detonation though. I will bring it back down to 35

Good job on the vacuum. AFR gauges are great! Just remember a miss fire will read lean, always check and read the plugs.

When reading the plugs, how long must it be driven to get a good reading on the plug? Once it's read and you change a setting, do you put new plugs in every time?

Originally Posted by 53 Chevy5

When reading the plugs, how long must it be driven to get a good reading on the plug? Once it's read and you change a setting, do you put new plugs in every time?

You'll be able to see changes pretty quickly. With the AFR gauge we'll stick with same plugs for now, just need to confirm what the gauge is telling us. After it's dialed in, new plugs and a fresh read.

We're getting close now. I have the 82 primary with the 56/40 needle and its running at 13 cruise and 11.5-12 WOT, that is an average of course, it's real hard to read perfect because of the constant rpm change on WOT. I'll try the 56/48 rods tomorrow and see how it acts. Holley recommends 13.5 cruise and 12.5 WOT, what are your thoughts on that? I know on my gauge as soon as it hits 14 the bar goes into the yellow instead of green. Another question is the AFR gauge will climb to 13.5 -14.5 if I'm climbing a slight hill giving it a little extra gas, is this normal?

On a side note this is kinda fun noticing the changes in how it runs. For the first time since I've owned the car it broke the tires loose when I shifted to second, not just a chirp or a squawk. It has 3.23 gears so their a kinda tall for grabbing rubber in all gears.

Almost there, 11.5-12 WOT is GREAT (I prefer this for WOT). What do the plugs say?
13 cruise is a good cruise, but a little on the rich side. Great for responsiveness, but mileage will suffer a little. 14 is a better compromise (let me think about the work around on this). What do the plugs say?
13.5-14 on slight load means the enrichment circuit is not coming in soon enough, install Heavier springs and it'll pull better.

Here's a chart that will help;

Here's a spring chart that will help;

Install the 58/44 rods, it will lean cruise and WOT slightly.

I think I just got myself into trouble. The TA carb It's getting closer to being tuned in, and I would like some real world 1/4 mile times to compare some adjustments. I was wondering how to measure times accurately and then all sudden I thought, there has to be an app for that, yep, I was right lol. I found one that will start as soon as your car starts moving, and it will measure and keep track of anything you want. This could end up costing me some money lol

Here is my nightly update, I drove it again with the 58/44 rods in and it seemed like everything was just a bit rich yet, low 13's and low 11's, a bit richer than what I thought it had the other night. I put in the 60/50 with the 82 primary that are in now vs the 87 that were in there the last time I tried them and my numbers are nearly perfect. 13.5-14 cruise and 12.5 WOT , 12.5 is leaner than you like, but still good? The only issue I have yet is it will still lean out with slight throttle up to 15-16, and that is with my heaviest spring, the silver one. The motor does start to run out of steam at about 5000 rpm's but it seems to pull real good up to 4500 ish. I was thinking about bumping up the secondary jet again. every time I type this the engine is too hot to pull plugs for you