Y07_A66

I have been dealing with multiple engine issues, with the carb just being part of it. I had a bad problem with rotor phasing (resolved a few months ago), and most recently I have been dealing with pulling oil into the intake at the valley pan gasket (BB). The weather was good today, and I was inspired to take the car out and tinker. I loaded my tools and IAB and MAB kits and hit the road.

Unfortunately, increasing the MABs didn't help; in fact it appeared it made the situation worse. At this point I can get reasonable numbers at 2K cruise (45MPH), but at highway speeds it still goes pretty rich. Today I increased the MAB from .033 to .035 and at 3K (@65MPH) the AFR was swinging more wildly than in recent memory, moving almost 2 full AFR (from high 11's to mid 13's).

Earlier experimentation lead me to believe my mains are over-emulsified, so I have change my emulsion jets to .028, blocked, .028, blocked (was .028, .028, blocked, .028). With the MAB at .033, this helped control the wild swings. However, the MAB at .035 has brought this problem back. It seems I am getting too much air into the main jet mixture at small throttle openings.

I then reduced the MABs to .031, and this reduced the AFR swings at 3K. Right now, I left it here.

Previously I had convinced myself that the motor was only getting fuel from the transition at 3K cruise, but your experience made me question that. I came to this conclusion because changes in the main jets didn't seem to be having an effect on the cruise AFR, but in hindsight expecting to see the effect of a couple jet size changes with the AFR swings that are occurring is a little foolish.

Anyway, after reducing the MABs, I tried a second experiment of increasing the IABs from .069 to .072. This did help the 3K cruise AFR some but it still bounces from the high 12's to the mid 13's.

How steady is your AFR at highway cruise? Do you use vacuum advance? Have you ever checked to see what difference there is with the vacuum advance hooked up and plugged, with no other changes?

Hopefully I will get a chance to check the plugs during the week. If I solved my oiling problem, then I should be able to fully concentrate on the carb setup. I am pondering with the idea of hooking up an in car video so you guys can see what happens at highway cruise. I'm also stewing on whether my problem is in the emulsification, and whether to try reducing at least the size of the first emul jet.

Doc,

I use an AEM 4100 setup. It is very entry level but seems to work well enough for basic tuning. I have an O2 bung in each bank, and move the single sensor from side to side while testing. I figure once I get everything dialed in, just leaving it in one side to monitor the motor should be fine.

Dave:

""How steady is your AFR at highway cruise?""
- At a steady throttle, the reading is very smooth (exp: 14.4-14.6) and I take the average to write down. I have seen a larger swing but that was when I was running leaner on the transition circuit. Overall, I would have to say that the guage reading is smooth. Sorry that I can't help you out on the guage swing, but do you have any air leaks on the exhaust "before" the bung?

""Do you use vacuum advance?""
- No. I have a FBO distributor and he plugs them up.

""Previously I had convinced myself that the motor was only getting fuel from the transition at 3K cruise, but your experience made me question that. I came to this conclusion because changes in the main jets didn't seem to be having an effect on the cruise AFR, but in hindsight expecting to see the effect of a couple jet size changes with the AFR swings that are occurring is a little foolish.""
- I can't give you an answer but I can tell you that I read an article to help find how to tell when your mains are coming in. The answer was to raise the main jetting by at least 4 sizes so that you will see a dramatic change in A/F ratio once you hit the mains.
I have found in reading about different brands of carbs, that each manufacturer may have a different opinion on if the carb should be running on the main circuit or on the transition circuit at cruise. My QF carb appears to be running on the transition circuit at cruise.

Doc:
I run the FAST #170634 analog unit. My exhaust is setup as two separate sides (no h or x pipe) and each side has a bung in the header reducer. I am only running one sensor and I have only tested it on the drivers side.

After my last test drive, I was looking over the new A/F numbers and I am curious about the A/F dip at 3500rpms:

40mph 2200rpms (16"hg) 15.4
50mph 2500rpms (18"hg) 14.6
60mph 3100rpms 14.4
65mph 3300rpms (17"hg)14.4
70mph 3500rpms 13.6
75mph 4000rpms 14.6

Is this A/F dip showing when the main jetting is starting in or is there something else? It seems weird that it takes almost a 1.0 dip in between the 3300rpm and 4000rpm range.
If this is the main jet, should I lean out the main jets by one or two sizes and restest?

Thanks

Hay guys ... more interesting stuff ...

YO .... do you have corresponding vacumn readings with those MPH, RPM and A/F #'s ?

Doc,
I updated my last response with the hg numbers that I have.

Thanks

So YO ....

Why do you think the A/F #'s are better at a faster speed ....70 vs 75 mph ?

Better vehicle aero at a faster speed? ... better efficiency of the motor at a higher RPM ?

""Why do you think the A/F #'s are better at a faster speed ....70 vs 75 mph ?""

Honestly, I do not know. I am thinking that if the mains are starting at the 3500rpm mark, then maybe at 4000rpms more air is being pulled into the main circuit which is leaning it out to the 14.6 AF.

Thank you.

I think you guys may be way overthinking this. Carburetors are not perfect. If they were, nobody would have spent the money to develope EFI. If you are going to agonize over every data point then you need EFI instead of a carb and you can expect to spend many hours tuning it to get the perfection you are shooting for.

I understand that a carb is not perfect. I also understand that certain areas of the fuel curve will be better/worse than the other areas. I am just trying to figure out how much of it I can tune out and how much of it I need to live with. I have a feeling that I am probably to that point.
Plus, I am learning more about tuning a carb as I go thru this process, which I enjoy.

Thank you for your perspective.

Y07_A66

"do you have any air leaks on the exhaust "before" the bung?"

I can double check this, but the AFR appears to swing to the rich side. There are some interesting posts on Innovates forums, and I speculate that I may have some fuel "spitting" from the main booster, due to too much emulsification. This loosely fits with my experience of changing the emulsification, and reducing the MABs. However, given the other problems such as pulling oil into the intake, it is hard to be definitive.

"I read an article to help find how to tell when your mains are coming in. The answer was to raise the main jetting by at least 4 sizes so that you will see a dramatic change in A/F ratio"

I have had from 76 to 71 main jets in it. Again, I am cautious to make any firm conclusion, but I did not see any major change in the AFR or swing. Of course there could be some small change, with that change buried in the swing. If I have fixed the oil issue, then perhaps I should re-do that experiment.

It is still my general belief that my engine is running almost exclusively on the transition at highway cruise (22" vacuum) but it is not clear to me why the fuel mixture gets so unstable. Perhaps there is another, non-carb, issue with the engine. I'm pretty confident the ignition is in good shape now (Mopar Distributor, 6AL-2 box).

I wonder if the top of the transition could be leaned out with the idle air bleed?
Maybe the mains could be delayed with the high speed bleeds?

Either way, if that is not a common cruising rpm for mileage concerns I would leave it alone and drive for a while. 12-13:1 is rich but shouldn't foul plugs or cause a dead or jerky spot in the revs right?

Good luck and thanks again for the tuning log

rdr

""Either way, if that is not a common cruising rpm for mileage concerns I would leave it alone and drive for a while.""

Good point Radar.
Thanks for the response.

Nice job of documenting your tuning process. One item that jumped out at me was you saying that you did not have vacuum advance. Is that correct? It appears that you have basically a street car and that you're spending a lot of time cruising at highway speed. That is the perfect application for vacuum advance so I'd recommend that you go back to a stock type distributor. Adding in a bunch of ignition advance at cruise can really help the engine run more efficiently.

Andy,
That is correct, I am not running a vacuum advance distributor. Several years ago when I sent in my dist to FBO, I got it back with the VA plugged and I have always just left it that way because it was working. I thought that if I had any issues with it than I would change it back out for a VA unit. Now I have a better reason to reconsider that.
Thank you for your reply.

Jim,

That is a very interesting thought. Hopefully the weather will be good this weekend, and I will play with the float level and see if it has an effect on behavior.

Prior to changing the emulsion jets the AFR swings were larger than they are now. There was a .028 in the first and second bleed, and now I have a blank in the second hole which seemed to help. As you say, perhaps the fuel level is sitting right at the first bleed. On the sight glass, the fuel level is in the middle which maybe is too high.

What sort of gaskets do you use in your carb? The reason I ask is that I have wondered whether under high vacuum there is fuel being pulled from somewhere where it should not. My carb is a QFT Q-850-PV (vac secondary), and have had trouble with the blue "non-stick" gaskets that it came with. They were sticking really bad all the time, and the aluminum of the carb main body was getting some oxidation on it. The guys at QF said it was from water (apparently the gaskets dissolve with water), but I suspect it was from the E-10 fuel that we have here. I wonder if the fuel additive can carry more moisture. Any way, I now use the Buna-N rubber gaskets which don't stick and I think they seal well but there is always that concern in the back of my mind.

Thanks very much for the thought. I'll report back as soon as I can try that experiment.

Dave

Hi again Dave:

I re-read your last couple of posts. Can you confirm that your current two e-bleeds are in the same position as the "old" Holley setup? I'm more familiar with the 5-e-bleed blocks, and am not sure how 4 positions work out WRT the the old Holley setup. That's always a good place to start, regardless.

Since your cruise is so rich, you might have better results lowering the float level below the top e-bleed. That way the top e-bleed will suck air at low main circuit flow. If testing confirms that your engine likes this, you could always move the upper e-bleed to the top position and reset the float level back to the sight plug.

Have you ruled out t-slot restrictors?

J

Jim,

I have an old Holley 750 and even older 780 that I can pull the metering block off of, and see how well the height of the e-bleeds match with my current metering block. The QF block has 4 holes, drilled at .028 and tapped at 6-32. When new, only the 3rd hole from the top was blocked. I guess it is reasonable to assume they had a reason for leaving the top 2 .028 holes unblocked. Does that seem like a lot of bleed air to you?

As I mentioned, changing the setup reduced the AFR swings, but did not eliminate it. And the cruise AFR was still pretty darn rich.

To add insult to injury, tonight I pulled spark plugs and although my oil sucking problem is much improved, it appears there are still a couple of plugs with signs of oil getting into the chamber. So, I'm going to have to take another attempt at the pan gasket sealing. Given that it is pulling oil, it must also be pulling some air, but perhaps it isn't enough to really upset the AFR (or this thing would be even richer than it is!).

You may yet talk me into the transition slot restrictors, but I'm still trying to get my off idle transition right just with the reduced IFRs. My concern is that the t-slot restrictors will just make this task harder.

BTW, here are the details of my setup:
70 Cuda, 400/470, E-head, 10.8:1, 248*@.050, 112LSA in at 109, RPM intake (recently switched from M1 SP), 1 7/8 TTIs, full 3" exhaust with X pipe and Ultraflows. Carb Primary setup: IFR .034, IAB .072, jet at 73, 6.5" PV. Motor pulls close to 15" vacuum in park at 1000, and bounces a bit between 9-10" in gear at 700 (factory 440 convertor at the moment). The M1 use to bounce 8-9" in gear. Secondarys are disabled via adjusting screw on the QF vacuum pod since I'm trying to tune the primaries only at the moment.

At one time, I did check the fuel level relative to the top bleed, and felt it was below it. But I will definitely double check as you suggest, since it was hard to make a great measurement.

I should get a chance to tinker over the weekend, and will report back.

Dave

Dave and Jim:
Nice info. Keep it coming.


I now have a problem with my O/2 sensor. It only reads 14.6 on my A/F gauge. This just started two nights ago when I started the car. It just quit taking the readings. It does not fluctuate at all with the accel pedal now, and it just reads the 14.6.

Last night, I checked the voltages at the gauge electrical connector and it showed (engine off, key @ RUN position):
Blue: 12v (12v ignition switched)
White: 0 (or 12v when lights are turned on, light source)
Black: 0 (ground)
Green: 2.5v (analog output)
Brown: 12v (12v constant battery)

I asked in another thread, what can make an O2 sensor go bad and the answers did not apply to my setup. So I am assuming that I might have a bad sensor already after just eight test drives and a few start ups. I am going to get under the carpet to make sure that the sensor has not come disconnected and I will also check the wiring as it comes thru the rubber boot in my floor pan.

Note: Rich says that a 14.6 reading usually shows the O2 sensor is not hooked up or the O2 heater has gone bad. He gave me a test to run to see if the problem is in the sensor. I will check back when I know more.

Can Autozone test an O2 sensor "off of the car"? If so, then I will take the sensor in to them to check it out. UPDATE: My local store said that they can not test O2 sensors.

Any thoughts?

Thanks

Y07_A66:

I don't know that much about the O2 sensors themselves. The two things that I have heard that kill them are operation with leaded fuel and running the engine without the cable connected to the sensor (I believe because the heater is not operational). I guess they could get totally fouled by carbon as well. I recently swapped my sensor from one engine bank to the other, and it did have a lot of carbon on it (since under some conditions my engine still runs pretty darn rich), but not of the holes where clogged or anything. I just wiped the carbon off before re-installing it.

Did you pull your sensor and examine it? Does your system have any sort of power on check routine that occurs when first starting your engine?