4 corner and 2 corner idle work the same way. The secondaries even on non adjustable still have an idle mixture discharge port, a transfer slot, and an idle air bleed and idle jet(IFR). It just can't be adjusted. 4 corner idle gives much better idle quality and cleaner emissions at idle, ESPECIALLY on modified engines.

 

Well, I am sorry for the absence. I have been traveling a lot and not much time to play. I have gotten to drive her to work a few times and tweaked the tune both leaving and going (50 miles). Since I posted last, I gave up on tuning the Pro Systems metering block and went for a Quick Fuel billet metering block in the front and back so I can more easily change the emulsion, PVCR, and IFR settings. The billet block has 5 ports (the second one up is blocked off), so it is a little different than the stock style block Patrick sent me. I like it, but I am still scratching my head on a few things. Billet block came stock with emulsion ports (.028, .028, .028, 0, .030), .035 IFR, and .055 PVCR.

I am attaching a graph of my latest WOT pull from 3rd gear (leaving at about 2000 and shutting down at 7000). As you can see, the left and right bank switch at about 5000 rpm and I have duplicated this numerous times. I would like to get the WOT a little richer but I am making small changes so I do not over shoot. I am also attaching a cruise graph. I was running a 75/84 Jet with a .055 PVCR. This was pretty good, but resulted in low 12s AFR while at cruise. I am currently running 72/85 jets with .063 PVCR. I know have the cruise at 13.0 or so. When I open the throttle up, it goes to 15:1 until I hit the PV then it comes back to 13.5 or so. Under WOT, It stays around 13:1 on a normal pull.

What is interesting, is I cannot get the cruise AFR to come up unless I jet down which is a double edge sword because then when I open the primaries, it goes too lean. I really cannot run any leaner jetting without is stumbling around. I had to increase the IFR to .036 to get the transition slot AFR at high idle so that is was not too lean. I have tried increasing the top emulsion from .028 to .031 but it did not have much affect. Lowing the fuel level of the bowl so that it is right at the bottom of the sight glass helped increase the cruise AFR a little, but nothing has gotten it to mid 13s except smaller primary jets.

Interestingly, at cruise, if I keep the throttle at the same position and push in the clutch, the AFR climbs to mid 14s, but when the engine has a bit of a load on it, the AFR drops to 13. Is it odd that a lowed engine has a richer AFR?

The red line is RPM, purple is drive side AFR, and black is passenger side AFR. As you can see on the WOT 0-120, I launched off the two step (high AFR), spun for about 5 seconds (see the rpm spike then come down then go back up, and started ripping off feet as I shift gears 1st-4th. My driver side sensors keeps locking up...need to do another beta firmware upload tonight, so you see it go flatline around 4th gear shift. Not the best pictures, but the snipping tool is the only way I know to get these into jpegs.

 

My next plan is to increase the top emulsion port some more and possibly the next one down too. I am also going to increase the secondary jet another size and possibly go to a larger PVCR as well. If I could just get a handle on the cruise AFR, I would go a jet richer on the primary too, but I know that will currently through the cruise AFR into the 12s, which is not terrible but starts to suck down the groceries pretty fast on a highway drive.

 

Use a power valve with a lower rating, duh. :P The power valve doesn't HAVE to be half of vacuum rating at idle. Remember in a post a long time ago I mentioned that modern performance engines are much more efficient at moving air at part throttle, so they sometimes need a PV rating that's only 2-4" below vacuum idle rather than half? It's to account for additional air being moved sooner at lower throttle openings.

In this case you jet it down to get the right cruise AFR, but on light throttle accel it leans out because the PV is not open yet....so put a PV in that opens sooner, should resolve the issue. Remember the PV is a transition part, it doesn't have to open at a hard and fast set point, but it needs to open when additional fuel is needed under part throttle accel....whatever that point may be. It's the transition circuit between cruise and WOT.

 

67Mustang302, I am with you on the PV. That is kinda what I have already done. My idle vacuum is 10", so I run a 8.5" PV. At cruise; however, my vacuum raises to 15"+ and does not drop below 8" unless I am really opening the throttle...dang near to the secondaries. For the reason, I cannot totally do what you are suggesting, which is why I am playing with emulsion ports to try to fix the cruise. I have jetted down the primaries quite a bit and opened up the PVCR quite a bit to help with this, but it will not get me all the way.

 

I opened up the top two emulsion ports last night and drove the car this morning. Interestingly, I saw absolutely not difference in the the AFR curve. I am running a HSAB of 36. The emulsion ports started out of the box as starting at the top and going down .028, .028, .028, blank, .030. I then went to .031, .028, .028, blank, .030. Last night I went to .033, .031, .028, blank, .030. I have seen no difference in the AFR curve through these three changes. I still have a rich cruise with a slightly lean partial throttle (open primaries no PV no secondaries). I wonder if the reason I am not seeing any change is because my HSAB is not big enough to feed anything but the top emulsion port and some of the second...

On another note, I am running the fuel level in the bowl right at the bottom of the sight glass. That puts the top emulsion port above the fuel level and the second emulsion port right at the fuel level. I know the fuel level of the bowl and the fuel level of the main well are not directly proportional, but dropping the fuel level of the bowl from 1/4 sight glass to at the bottom of the sight glass did raise my cruise AFR from mid 12s to 13:1. Any ideas on this?

I wonder if I should just block off the top emulsion port as it does not seem to be doing much and is possibly taking most of the air.

 

if have mine (front and back) at about quarter sightglass (lower quarter). if i have them where the sightglass starts i start to get problems with off idle bogging. car seems to be happier with the quarter in there

 

Yeh, I have that issue too, but if I raise the fuel bowl level up much, the cruise AFR goes down into the 12s and my highway mileage (not a huge concern, but running stinking rich is) begins to really take a dive. I read somewhere just yesterday to run street cars at the bottom of the glass and race cars at 1/4 glass. Man, my memory is bad, because I cannot find it today.

Edit: I found it! AED's website suggests bottom of sight glass for street cars and 1/3 of the way up for race cars.

 

Well, on the advice of QuckFuel, I tried a larger HSAB. I went from a 36 to a 40 and saw little difference in the cruise AFR and a leaning of the AFR during WOT. That is what I expected, so half way home I pulled over at a gas station and made a emulsion change. On the advice of 67Mustang302, I moved the blank emulsion to the top port and set all the others to .028. The car TOTALLY hated that. the cruise AFR was way richer (went from 13:1 to 12:1). It was also dead lean if I cracked the throttle much. It would go to 15:1+. I guess that was the wrong direction to go. Apparently the top port is doing something. When I got home, I changed the emulsion ports to (.035, .028, .028, blank, .030) from top to bottom. My wife and son were feeling neglected, so I did not go for a test drive. I am back on the road for work for the next 10 days, so I will report back sometime at the beginning of the month.

 

At least you know it reacted to the change.

Try 35 33 28 blank 30 maybe?