4180 AFR tuning

[Saturn V]

Seeing BaconB8's tuning thread motivated me to post my experiences and questions and it will be interesting to see his results, too. I bought my 84 GT 3 years ago and it came with what appears to be a freshly rebuilt 80163 4180 service replacement carb. Sadly, the gold dichromate finish was stripped.

Tuning by pulling and examining hot spark plugs always seemed like voodoo to me (no offense to those who have mastered that art ... reading plugs, that is) so I bought an Innovate LM-2 air-fuel ratio meter and data logger. I also purchased the clamp-on tachometer input to record engine speed. I finally got the O2 sensor installed a few months ago. The guy at the muffler shop did his best, but I now realize that the job would have been a little cleaner if he'd taken a wire wheel to the pipe to scrub off the oxidation, first. The location that I chose for the O2 sensor is the part of the factory y-pipe that comes from the driver's side exhaust manifold. There really wasn't any other place to measure the exhaust upstream of any cats. This arrangement probably has drawbacks (like not measuring the other bank of cylinders) but I didn't think installing another O2 sensor on the passenger side (which would have been almost impossible to access, upstream of the lightoff cat) would make much difference.

[Saturn V]

After installing the Performer 302 intake couple of months ago, the idle didn’t seem as smooth as before. I tracked down a couple of small vacuum leaks and battled defective (apparently) new temperature-controlled vacuum switches, but there was still what felt like an occasional light miss or stumble at idle … not bad, but enough to be noticeable.

While starting the idle mixture tuning process a couple of weeks ago, the engine wouldn’t start at all. This was just after installing new Autolite 25 plugs. After confirming that the ignition was OK, I pulled the fuel supply line and cranked the engine … no fuel. How is it that the fuel pump appeared to be OK a few days before, I pulled into the garage, and then a few days later after replacing the spark plugs the engine would not start and the fuel pump won’t pump? Oh well. I put in what I could find at O’Reilly, but may find a good Carter later. After installing the new fuel pump, I adjusted primary and secondary float levels (carefully) with the engine running.

My carb only has mixture screws for the primaries, not the secondaries as some have. Maybe it’s because my carb is a service replacement? I used a 3/32” Allen wrench about 3 inches long. Next time I’ll get a second wrench so that I can leave one in each idle mixture screw. Swapping the wrench from side to side and trying to get the wrench into the screw socket each time with a hot, running engine wasn’t easy. Anyway, the best I could get manifold vacuum at 800 RPM was 19.5 inHG with AFR around 13.0. This seems rich to me for idle. Below is a table of the results. All are with a bare carb at about 800 RPM, except for the last line when I installed the air cleaner, which leaned out the mixture a little . I measured the number of turns on the idle mixture screw as precisely as I could, but these may not be exact.

Prim Idle Screw Turns Open (both sides)	AFR	Vacuum (inHG)	Notes
1	17.0	15-17	Too lean, vacuum fluttering
2	13.1	18	Vacuum fluttering
2	12.0	19.5	Fixed a vacuum leak, vacuum steady now
1.5	13.4	19.0	Steady vacuum
1.75	13.0	19.5	Steady vacuum
1.75	13.4	19.5	Re-installed factory air cleaner

[Saturn V]

This carb came on the car when I bought it 3 years ago, but I think it needs a rebuild for the following reasons.

• The engine has always been a little hard to start when cold. I have to dry crank the engine for about 10 seconds and then pump the throttle 5-8 times to get it to start when cold. And it actually seems to be worse since replacing the fuel pump and adjusting the idle mixture.
• The AFR is really rich (10.8:1) at full throttle.
• After the new intake installation, I pulled the carb and noticed that the carb base gasket was getting soaked with fuel.

I’m having problems with the clamp-on tach input for the Innovate LM-2. I think the clamp got a little too close to the exhaust manifold and melted a little. Now it doesn’t consistently measure RPM. So I’m going to refer to a trend that I recorded a couple of months ago, before the new Performer 302 intake installation, new fuel pump, and idle mixture adjustment. However, I haven’t seen any big difference in AFR trends at full throttle after these steps. The purple trend is air fuel ratio (AFR) and the black trend is engine speed.

• Why the sudden lean spike in the middle of first gear at full throttle?
• Why the double lean spike at each shift? I know the throttle is closing, but am curious about the double spike.
• What could cause the AFR to be so rich at full throttle? It gets as low as a bout 10.8:1 in first gear. Could the o-rings in the accelerator pump transfer tube be leaking? I assume the primary jets are original, as well as the secondary metering plate. I’ll find out soon when I rebuild the carb.

[8ballEinstein]

I can see this is going to be interesting to analyze and I'm sure I'm going to learn a lot.

I'm going to guess the first spike was a result of the secondaries opening up. From there, the fuel came streaming in to a really rich level. On the double spikes, I'm taking a stab at that being the two-stage power valve closing.

If I was tuning from here, I'd start by using a heavier secondary spring. But I'm just an amatuer at this.

[BaconB8]

Good post. Loaded with data and not swag-based tuning. I'll be generating some hopefully this afternoon for all to see.

There may be some additional vacuum to be had in some small places. I found my egr spacer to intake manifold gasket had a small tear, allowing a vacuum leak and exhaust gas to run unchecked into my intake stream. You might want to check yours if you haven't lately. I also found the pcv valve hoses had small cracks from heat, and if they are leaned against or wiggled would allow air to get under the carb baseplate. Does your car still have the thermostatic air valve on the pcv hardline? In playing with mine, I found when it opens it can lean you out by about 3/4 of a point. It may be worth checking incase its stuck open or opens under wot causing that lean spike.

With fuel as costly as it is, it doesn't make sense to guess anymore. The extra power is icing on the cake.

[Saturn V]

I can see this is going to be interesting to analyze and I'm sure I'm going to learn a lot.

I'm going to guess the first spike was a result of the secondaries opening up. From there, the fuel came streaming in to a really rich level. On the double spikes, I'm taking a stab at that being the two-stage power valve closing.

If I was tuning from here, I'd start by using a heavier secondary spring. But I'm just an amatuer at this.

I sure hope to learn from the "carb masters" here and am glad we have a forum like this to share and archive useful information. I had always thought that the secondaries opening too soon would cause a rich bog, but perhaps it causes a lean condition? I don't really notice a bog, but will probably try some different secondary springs. I'm planning to get the Holley quick-change spring kit. My data logger has the capability to log additional signals and I'm thinking about temporarily installing a micro switch to detect when the secondaries open. I've got a spare heat shield that's been cut up that I think I can mod to accept the micro switch that I already purchased. You may be right about the power valve causing the two spikes.

Good post. Loaded with data and not swag-based tuning. I'll be generating some hopefully this afternoon for all to see.

There may be some additional vacuum to be had in some small places. I found my egr spacer to intake manifold gasket had a small tear, allowing a vacuum leak and exhaust gas to run unchecked into my intake stream. You might want to check yours if you haven't lately. I also found the pcv valve hoses had small cracks from heat, and if they are leaned against or wiggled would allow air to get under the carb baseplate. Does your car still have the thermostatic air valve on the pcv hardline? In playing with mine, I found when it opens it can lean you out by about 3/4 of a point. It may be worth checking incase its stuck open or opens under wot causing that lean spike.

With fuel as costly as it is, it doesn't make sense to guess anymore. The extra power is icing on the cake.

I've not seen anyone post much information about using an AFR meter to tune a carb application, and now we're both doing this at the same time. I look forward to seeing your data, in whatever form you are able to share it. I used SnagIt for the screen capture and annotations.

I just put on a new intake a couple of months ago, so all carb and EGR spacer gaskets are new. I used a spray bottle set on stream to spray around the intake and carb based, but haven't found any leaks there. I might have missed some spots, though. Vacuum is actually a little higher now than before the intake swap, probably since I fixed a few leaks.

I'm not sure, but I think the thermostatic valve on the PCV hardline is only for 85. My 84 doesn't have it and I don't recall ever seeing a picture of an 84 engine that did. I don't know how it works, but am guessing that it is closed when cold (for what reason?) and opens to admit PCV flow when warm? Does it admit outside air, or is it only a valve that blocks/restricts PCV flow? Sorry for the digression, but I've wondered about this part.

My main interest is in getting the car to run the best that it can, which I believe should improve the mileage from 8 MPG to at least low double digits. But it rarely sees the freeway ... mostly just around neighborhood streets and boulevards, which brings fuel economy down, along with periods of idling while troubleshooting and the occasional "test pass".

[BaconB8]

A MAP sensor may be a good call. You'd be able to see where in the curve the PV is opening in relationship to vacuum/rpm and mixture.

[BaconB8]

I'm not sure when the inline temperature valve opens or shuts. I did open it manually. The mixture gets leaner and the rpm climbs a bit when its open.

I don't know if 83-84 cars have this. I only have 85's at present.

[8ballEinstein]

I sure hope to learn from the "carb masters" here and am glad we have a forum like this to share and archive useful information. I had always thought that the secondaries opening too soon would cause a rich bog, but perhaps it causes a lean condition? I don't really notice a bog, but will probably try some different secondary springs. I'm planning to get the Holley quick-change spring kit. My data logger has the capability to log additional signals and I'm thinking about temporarily installing a micro switch to detect when the secondaries open. I've got a spare heat shield that's been cut up that I think I can mod to accept the micro switch that I already purchased. You may be right about the power valve causing the two spikes.

You may not feel a bog during acceleration, but instead, the secondaries may feel like they're "kicking in". If so, what you really get is a flat spot in the acceleration curve, just ahead of the secondaries popping open. Ideally the transition should be smoother.

It looks like you would've had a double spike on your last shift but you eased off on the throttle .

[Ethyl Cat]

Nice data , what can you do with it?

My questions now are:
1. what was the vacuum during the spike? Tape you gauge to the windshield on the next trip.
2. Is the pump adjusted right?
3. What cam is it?
4. What position is the cam in?
5. What squirter is in it?
6. The real data you need is in the carb. Jet sizes, PV,Secondary spring, etc
7. What is the AFR on the other bank?
8. How is the primary blades relationship with the transfer slot?
and more

I think you need a shorter O2 bung the sensing element is being shielded which can scew the reading.

If it were me, I would pull the carb and see what I had, then we can figure it out.

All we know now is that you set the float and the pump is new

Steve

[Saturn V]

A MAP sensor may be a good call. You'd be able to see where in the curve the PV is opening in relationship to vacuum/rpm and mixture.

That's a great idea. I've started looking for a cheap sensor and harness.

Nice data , what can you do with it?
..............

Steve

Steve, thanks for your comments. You and JACook are a couple of the "carb masters" that I had in mind.

So far, the AFR data has provided some pretty compelling evidence that the carb is running way too rich at full throttle. And I did mention above that I plan to pull the carb soon for a rebuild and then I'll have a look at what I've got inside. I realize that I shouldn't rely exclusively on AFR data and shouldn't ignore reading spark plugs, and any other tuning methods, even if they are not familiar to me. I'm hoping to learn from all here.

The O2 bung does look longer than typical, and before installation I did speak to a tech at Innovate to confirm that it is correct. If the measurement didn't change very much, I'd be suspicious that the sensor isn't getting good flow, but it seems to be very responsive.

[bob85gt]

I have driven my car for about 15 years with a a/f gauge , but no data logger. which I wish I had one. here's my .02

the single spike is when the secondaries open up to quickly and it goes lean. then air starts moving and the a/f goes to 11 to 1 (or so)

when I look at the double spike I see the first spike as the throttle closing, the second is the secondaries opening. my question is were is the accelerator pump. this is to provide some fuel to prevent the lean spike. my guess is you need a bigger squirt , slower opening or a combo of the two.

I know on my car I can see the accelerator pump make the a/f go rich.

[Saturn V]

I have driven my car for about 15 years with a a/f gauge , but no data logger. which I wish I had one. here's my .02

the single spike is when the secondaries open up to quickly and it goes lean. then air starts moving and the a/f goes to 11 to 1 (or so)

when I look at the double spike I see the first spike as the throttle closing, the second is the secondaries opening. my question is were is the accelerator pump. this is to provide some fuel to prevent the lean spike. my guess is you need a bigger squirt , slower opening or a combo of the two.

I know on my car I can see the accelerator pump make the a/f go rich.

bob85gt, you might be right about the first spike in 1st gear caused by the secondaries opening. I don't really notice a bog or flat spot at full throttle, but admit that I don't really know exactly what this will feel like and am learning. I'll try to pay more attention. I do think I can feel the secondaries kick in when slowly rolling into the throttle in 2nd gear at other times, so I may need to tweak the spring.

Regarding the double spikes, both spikes occur as engine speed is falling, before I've completed the shift and mash the throttle again, so I think the secondaries are still closed here, as well as the primary throttle. I thought about disconnecting the secondary diaphragm and wiring the secondaries closed and make a data run for comparison.

[Ethyl Cat]

bob85gt, you might be right about the first spike in 1st gear caused by the secondaries opening. I don't really notice a bog or flat spot at full throttle, but admit that I don't really know exactly what this will feel like and am learning. I'll try to pay more attention. I do think I can feel the secondaries kick in when slowly rolling into the throttle in 2nd gear at other times, so I may need to tweak the spring.

Regarding the double spikes, both spikes occur as engine speed is falling, before I've completed the shift and mash the throttle again, so I think the secondaries are still closed here, as well as the primary throttle. I thought about disconnecting the secondary diaphragm and wiring the secondaries closed and make a data run for comparison.

I am going to agree with Bob85gt on the double spike. The first spike is occurring with the transition to closed throttle to make the shift driving the AFR lean. The second spike is/could be a lack of accel pump upon engaging the next gear and matting the throttle, a delay in secondary actuation, a delay in the main metering circuit, etc.

Notice rpm does not climb until the AFR comes back down. Is it time across the bottom in seconds? If so, then the car does not accelerate for 7 seconds, hard to believe that you did not say there was a hesitation or lag if I read it correctly.

When are you pulling the carb? Lets get this thing running right!

Steve

[Saturn V]

I am going to agree with Bob85gt on the double spike. The first spike is occurring with the transition to closed throttle to make the shift driving the AFR lean. The second spike is/could be a lack of accel pump upon engaging the next gear and matting the throttle, a delay in secondary actuation, a delay in the main metering circuit, etc.

Notice rpm does not climb until the AFR comes back down. Is it time across the bottom in seconds? If so, then the car does not accelerate for 7 seconds, hard to believe that you did not say there was a hesitation or lag if I read it correctly.

When are you pulling the carb? Lets get this thing running right!

Steve

Yes, the time scale is on the bottom. The time from letting off the throttle at the 1-2 shift until I'm back on the throttle and RPM increases is only about 1 second (~7.0 to ~8.0 on the trend). So I still think that the second part of the double spike is occurring with the throttle closed.

Now I think you and Bob are on to something with the comments about the accelerator pump. After the shift and when RPM starts to increase again, it takes about 1/2 second for the AFR to slide down to the "steady" AFR (~10.8 in my case). It's like the peak too slowly fades away. Perhaps with a larger/faster accelerator squirt, the "steady" AFR will be reached more quickly (even though in my case "steady" means really rich).

Yesterday I received the Holley quick change vac sec spring kit and springs. The quick change kit was the last piece I needed before beginning the rebuild. I think I'm going to rebuild everything back the way I found it, unless I find some really goofy primary jets or secondary metering plate carnage. This way I can have some consistent comparisons before and after. Then, based on more data and other suggestions here, I'll consider putting in larger primary jets (I've got 63's ready), the 31 nozzle, and maybe even the 34-6 secondary metering block conversion kit which I have ready. I could go ahead and do it all now, but I'm trying to learn a little about each mod as I go. I would start this tonight, but I'm planning to drive the car in the neighborhood July 4th parade tomorrow and don't want unexpected carb trouble to keep me out of the parade. Maybe tomorrow night or Sat I'll start on the carb.

[8ballEinstein]

Yes, the time scale is on the bottom. The time from letting off the throttle at the 1-2 shift until I'm back on the throttle and RPM increases is only about 1 second (~7.0 to ~8.0 on the trend). So I still think that the second part of the double spike is occurring with the throttle closed.

Now I think you and Bob are on to something with the comments about the accelerator pump. After the shift and when RPM starts to increase again, it takes about 1/2 second for the AFR to slide down to the "steady" AFR (~10.8 in my case). It's like the peak too slowly fades away. Perhaps with a larger/faster accelerator squirt, the "steady" AFR will be reached more quickly (even though in my case "steady" means really rich).

Yesterday I received the Holley quick change vac sec spring kit and springs. The quick change kit was the last piece I needed before beginning the rebuild. I think I'm going to rebuild everything back the way I found it, unless I find some really goofy primary jets or secondary metering plate carnage. This way I can have some consistent comparisons before and after. Then, based on more data and other suggestions here, I'll consider putting in larger primary jets (I've got 63's ready), the 31 nozzle, and maybe even the 34-6 secondary metering block conversion kit which I have ready. I could go ahead and do it all now, but I'm trying to learn a little about each mod as I go. I would start this tonight, but I'm planning to drive the car in the neighborhood July 4th parade tomorrow and don't want unexpected carb trouble to keep me out of the parade. Maybe tomorrow night or Sat I'll start on the carb.

Honestly, I'm not seeing a problem with the accelerator pump. You say you're granny shifting so you have a slight delay before you start standing on the gas again. And when you do, it looks like the AFR is plenty rich. But all just the same, I'm wondering what accelerator pump cam you're running.

The main things I would concentrate on are the secondaries opening too quickly (below 3000 RPM), and the really rich condition.Tackle those things and I think the rest will be a slam dunk.

Good luck, Erik.

[burntorange84]

Saturn

Haven't read the whole thread yet; but do please swap those Autolite's back to the motorcraft copper plugs.

Zap's (zaps85, i believe) got a thread on here about the many problems with Autolites these days. I too
posted on that thread.

I'll read more later when I have more time!

-j

[Saturn V]

Saturn

Haven't read the whole thread yet; but do please swap those Autolite's back to the motorcraft copper plugs.

Zap's (zaps85, i believe) got a thread on here about the many problems with Autolites these days. I too
posted on that thread.

I'll read more later when I have more time!

-j

Here it is http://vb.foureyedpride.com/showthre...rk-plugs-(long)

I do have a slight miss at idle that I've not been able to track down. I think it was there after the intake swap, but before the plug swap. Still, reading the thread above has me doubting the Autolites. But now I'm thinking NGK instead of Motorcraft!

I've got some more data after the carb rebuild this weekend, but don't have time to post details. Basically no change in full throttle AFR and now it's a little harder to start, which disappoints me.

[burntorange84]

*Why the sudden lean spike in the middle of first gear at full throttle?

I'd do a little testing here on secondary throttle activation. Once you stab (probably a bit slower transition than a 1 to 2nd mash the throttle) the throttle at low revs in say a non-tire trashing condition which is hard with these cars, the accelerator pump shot is done before the secondaries open. There can be a split second condition before the venturies start to flow fuel. On a vacuum secondary carb the flow thru the primaries actuates the secondary opening; there is no pump shot on the secondaries..at least in these 4160 style variants. Thus try your fast lean-in to full throttle at 3000 to 3500 rpm, say up a steep hill in first gear. I think being at higher revs will lessen the lean condition. This too could be a transfer slot issue on the secondaries as well as a spring change, but try that first.

*Why the double lean spike at each shift? I know the throttle is closing, but am curious about the double spike.

This is probably the close of the throttles and the transitions of the throttles to the idle transfer slot and idle circuits. It's in a no load condition and is not lean ~13:1. I wouldn't worry about it...

*What could cause the AFR to be so rich at full throttle? It gets as low as a bout 10.8:1 in first gear.

I assume you have a new/clean paper filter? Engine fully warmed up? I'd do a run with the snorkels and plumbing removed from the air cleaner assy. I'd take the 4 screws (2 per side) off the circular housing and do a few runs to see if any change. The stove/heat dampers are in a normally open state but it's always best to check an obvious restriction. You could do a pull with the filter removed too. It does seem too rich. but please swap the spark plugs first.

*Could the o-rings in the accelerator pump transfer tube be leaking?

It could but it usually leaks into the power valve chamber causing surges at idle when you have a high vacuum condition; not at WOT.

-j

[burntorange84]

I'm not sure when the inline temperature valve opens or shuts. I did open it manually. The mixture gets leaner and the rpm climbs a bit when its open.

I don't know if 83-84 cars have this. I only have 85's at present.

My 84 does/did....I plugged it with a npt plug. This was added for long idle conditions on the SSP cars originally so the idle would speed up and cool the engine by more fan movement. Mine leaked a very little bit and I was trying to solve idle issues so I removed it. There was no noticeable change after I removed it.

-j

[Saturn V]

*Why the sudden lean spike in the middle of first gear at full throttle?

I'd do a little testing here on secondary throttle activation. Once you stab (probably a bit slower transition than a 1 to 2nd mash the throttle) the throttle at low revs in say a non-tire trashing condition which is hard with these cars, the accelerator pump shot is done before the secondaries open. There can be a split second condition before the venturies start to flow fuel. On a vacuum secondary carb the flow thru the primaries actuates the secondary opening; there is no pump shot on the secondaries..at least in these 4160 style variants. Thus try your fast lean-in to full throttle at 3000 to 3500 rpm, say up a steep hill in first gear. I think being at higher revs will lessen the lean condition. This too could be a transfer slot issue on the secondaries as well as a spring change, but try that first.

*Why the double lean spike at each shift? I know the throttle is closing, but am curious about the double spike.

This is probably the close of the throttles and the transitions of the throttles to the idle transfer slot and idle circuits. It's in a no load condition and is not lean ~13:1. I wouldn't worry about it...

*What could cause the AFR to be so rich at full throttle? It gets as low as a bout 10.8:1 in first gear.

I assume you have a new/clean paper filter? Engine fully warmed up? I'd do a run with the snorkels and plumbing removed from the air cleaner assy. I'd take the 4 screws (2 per side) off the circular housing and do a few runs to see if any change. The stove/heat dampers are in a normally open state but it's always best to check an obvious restriction. You could do a pull with the filter removed too. It does seem too rich. but please swap the spark plugs first.

*Could the o-rings in the accelerator pump transfer tube be leaking?

It could but it usually leaks into the power valve chamber causing surges at idle when you have a high vacuum condition; not at WOT.

-j

I agree with the comment that you and others made about the spike in 1st gear. That must be the secondaries opening and fuel flow in that circuit hasn't started yet. The delay is only about a 1/2 second, so it's not as big a deal as it looks on the trend. I don't see the same single spike in 2nd or 3rd gear, but perhaps that's because the secondary metering circuit is already "primed" from the run up in 1st gear? I have noticed more of a flat spot when slowly rolling into the throttle before I feel the surge in power from the secondaries. I'm not sure if that means I need a lighter or heavier spring. I'm thinking lighter, since it pulls better after the secondaries flow fuel (I think). I'll try both, since I've got the quick change secondary actuator diaphragm cover installed now.

I think you're right ... the little double spike is probably just circuit transitions when closing the throttle and not a big deal.

The air filter is new and I did check to ensure there are no blockages in the fender air tubes. Stove dampers are open (and the actuators leak, so they never close ... I have disconnected and plugged the tubing for now to prevent vacuum leaks at warmup.)

Thanks for the comment on the accel pump transfer tube O-rings. There's practically no change in full-throttle AFR after the carb rebuild, so it can't be these, anyway.

That's interesting that your 84 had the little valve in the PCV tube. Is yours a really late 84? Mine was built July 84 and doesn't have the valve. Does the valve just bleed a little extra air into the carb to increase idle speed?

I'll try to make some time for more tuning this weekend.

[burntorange84]

That's interesting that your 84 had the little valve in the PCV tube. Is yours a really late 84? Mine was built July 84 and doesn't have the valve. Does the valve just bleed a little extra air into the carb to increase idle speed?

IIRC, mine was April of 84...I'll try to find my paper from Ford....but I wonder if it may be location specific for what cars got them. The Calibration on the valve cover should tell ya which you have. Yours was originally a Florida car, right?

BTW: I might be making it to Houston with-in a month or so...I'll let you know when I know more... My car is almost off the stands....it's been there for 2 years ...

[Saturn V]

IIRC, mine was April of 84...I'll try to find my paper from Ford....but I wonder if it may be location specific for what cars got them. The Calibration on the valve cover should tell ya which you have. Yours was originally a Florida car, right?

BTW: I might be making it to Houston with-in a month or so...I'll let you know when I know more... My car is almost off the stands....it's been there for 2 years ...

Calibration sticker is there, but long faded and unreadable. I bought the car in Florida, but don't recall where it was originally sold.

Send me a PM before you come to Houston, we should get together.

[Saturn V]

OK, it's been a while since I've done much with AFR logging. I did replace the Autolite plugs with NGK V-Power UR4s after some suggestions, but can't tell any difference in how the car idles or runs throughout the range. The Autolite's looked clean ... thought I had some pics, but can't find them now.

Today I decided to zip-tie the secondaries closed and log some data. After a couple of runs, I can see that the average AFR is about 12.5, what I'd like to see with the secondaries open. Even though my engine is basically stock, operating only on the primaries is no fun.

[Saturn V]

So then I removed the zip tie to let the secondaries breath again. I'm still getting the same rich mixture as during initial tuning a few months ago ... about 10.7 AFR at full throttle.

This carb is a dealer service replacement for 84-85, but I'm starting to think that maybe the secondaries are setup too rich for a stock 84. When I rebuilt it a few months ago, I kept the original secondary metering block which appears to be correct for 85. I do have the Edelbrock Performer 302 intake, but really couldn't tell a difference with it. Maybe I need to open up the exhaust to really feel the benefit of the intake? Could a carb tuned for a 210HP 85 engine really run this rich on a ~175HP 84 engine?

Any other ideas?