Just installed an AEM wideband o2 controller and gauge. My set up appears to be rich on idle and cruise then goes leaner at WOT.

at idle I show 11.5-11.8 AFR 950rpm
light cruise 10.5-11 cruising in 3rd and 4th gear
heavy cruise 10.00 gauge doesnt register it gets so rich
WOT 12.2-12.5



I have a supercharged small block and want WOT around 11.5-11.8 and I guess idle and cruise to be around 14s.

I installed the o2 sensor at buddies shop and didnt wire it until I got home, is it possible i fouled out the o2 sensor or something? my reading seem off.

 

talked to AEM tech and he said that when an o2 sensor goes bad it will read full lean and he has never seen one read that reads too rich on error. he told me to pull sensor out and explained how to do a simple test on it. The sensor was not fouled and passed the test procedure. Maybe my idle circuit is just off, it does have a slight gas smell at idle and the exhaust pipes look pretty black at tips. however the spark plugs were all brown and none were fouled black? the car does get horrible gas mileage..7mpg lol

I'll have to try and tune carb on sunday and see if I get a change in AFR readings.

 

You did not say what carb you have? But you have several things going on.

Idle is not primary jetting. You have to drill holes in the primary throttle blades.

air bleed changes can actually cause a motor to be able to run with smaller jets.

Rich at cruise is all primary jetting

Wide open throttle is a combo of all circuits, but secondary jetting is the only addition.

 

Check out the innovate tuning forum http://www.innovatemotorsports.com/f...isplay.php?f=7

Your problem is very common with performance carbs. It can be improved but it's quite a bit of work.

 

As long as your idle mixture screws have good o rings in them and there is no vacuum leaks, you can lean your idle AFR from where its at to 14.0 or so..... Part throttle AFR is controlled by a combo of air bleeds and primary jets. If you have a box stock holley DP, the air bleeds are not adjustable so you have to just live with it. Your WOT is easily tuned with a jet size increase. Here is what I recommend to get you started....

1)Remove and plug rear PV, then go up about 8 jet sizes from the current rear jets.....(Measure AFR again and adjust as necessary)

2)Install rear jet extensions and get a notched float, set flow height correctly.

3)Adjust your idle mixture with a vacuum gauge connected and engine fully hot, adjust all 4 mix screws equally to get the highest vacuum....(although I am not sure how this will work with a blower in it, it may screw up the vacuum readings)....Once this is done, your idle mixture will likely be around 15.0 afr....you can richen it back up some a tad if you want....Sometimes this is necessary on automatic cars to get a good idle IN GEAR but since yours is a stick, you should be fine...


Once you get the idle mix correct and your WOT afr is correct, you will have to see where your cruise AFR is....odds are its gonna be a little rich, that is pretty typical, you CAN go down two sizes on the primary jets and it will lean the cruise AFR some but you will have to go UP on the rear jetting to compensate to keep the correct WOT AFR.... BUT you don't want TOO much spread between the front and rear....you will already have a big enough spread from not having a PV in the rear and jetting up for it....

FWIW, just to give you a ball park example, I have 80 jets in the front WITH the PV and 90 jets in the rear with no PV....This gets me 11.8 AFR for most of a pass....Freeway cruise is around 12.8.... a tad rich but I live with it....helps with detonation prevention.


You will just have to play with it to see what it wants... I tend to like the idle mix around 14.0, cruise mix around 13.0-13.5(leanest) and WOT around 12.0-12.5 on NA motors..... Blown/turbo motors I get em in the 11.5 range...

 

carb is a 750cfm barry grant mighty demon blower carb with annular boosters. the PV for primary side is boost referenced.

part #
5402010BC




It bought it new last fall and set it up following instructions. I set up the throttle blades so .020" of slots are showing and I set up float levels with bowls off and up side down and made sure I had .400-.500 of clearance between top of floats and float bowl. both float levels are between middle and upper line on sight glasses.

I bolted it on with stock jetting and PV, went to dyno and the AFR was 15.1 at WOT and we couldnt make a full pull. The dyno guy jetted both sides up about 8-10 jet sizes and got the AFR down to 12.5-12.8 at WOT and left it there. He never checked AFR at any other RPM and didnt touch any other thing on carb.

here is my set up at a 900rpm idle! too rich, vac is low, fuel pressure too high? disregard the white wire its for the gauge lighting and I have since finished wiring it.


I'm going to pull carb and check jetting and start over with tuning it. I'll try and get the idle set to highest vac and around 14 AFR, and then I'll tune secondary jetting for WOT and get it down from 12.5 to 11.5. Then I'll worry about cruising AFR with primary jetting. To re-adjust idle to 850-900rpm I should use the two butterfly screws??? or do they need to remain at .020" gap? I have a screw where air cleaner stud goes thats for adjusting idle... but I saw no change in rpm when turning it?

One weird problem I'm also having is with idle, when I start car and when its idling in backyard its at 900-950rpm. But when I drive and stop at light it idles hight 1100-1300rpm and if I sit there at light for 20sec or more it slowly drops back down to 1000-900rpm. This could be a throttle return spring issue?

 

Thanks for the info, I should be able to follow this set up and I already have a Vac/boost gauge for setting up idle.

Im pretty sure that my blower carb doesnt have a PV in secondaries, I'll find out in a few mins when I pull carb off.

What are jet extensions and what is the benefit of using them? are they used on both pri and sec or just sec? is a notch float for clearance issues with jet extensions?

sorry for questions I'm still learning here lol

 

the carb had 86 jets in primaries and 92 jets in secondaries, and 4 idle mixture screws were 1 1/2" turns out. The front PV is boost ref and there isnt a PV in the rear. The air bleeds are changable.

I downsized fronts to 82 and backs i went up to 94, set the 4 idle mixture screws 1 1/4" out. I set the primary throttle blades at .020" slot setting and this time I set secondaries to the bottom of the slot so slot isnt visible. I started it up and let it warm up and it idles 850rpm vac is only 9-10in Hg and AFR was 11.8-12, slighty leaner then it was before and i didnt even play with idle mixture screws yet. It was getting late and my cars pretty loud so I'll have to tune it tomorrow afternoon.

I checked into jet extensions and there are two types:

http://www.jegs.com/i/Barry-Grant/132/120001/10002/-1


http://www.jegs.com/i/Holley/510/122-5000/10002/-1

 

It has a lot of jet in it BUT I think BG uses their own jet rating system that is different from holley, not to mention the high speed air bleeds can affect jetting so I can't help with you what it needs....You will just have to trial and error.

If your fuel pressure gauge is accurate at 9.5 psi, that is normally too much for a holley need/seat and I am suprised its now flooding through the vent tube or boosters.....That may be why it idles so rich. I would set the fuel pressure back down to 7-7.5 psi when hot. The idle mix screws will clean up the idle afr completely...

The purpose of jet extensions is when drag racing from a dead stop, fuel will flow away from the jets/metering block on the launch and can cause a lean out in the lower gears.... Putting extensions in the secondaries pushes the jets closer to the rear of the blow keeping them submerged in fuel. Yes the notched float is to clear the extensions. This is really not necessary unless you are launch hard or the car pulls REAL good in 1st.

Just keep tweaking it and make 1 change at a time and see what it does....Youll get it right. Keep the timing conservative while tuning..

 

I ordered an aeromotive fuel reg and will be installing it friday to bring fuel pressure back down to 7-7.5psi range.

Did a little tuning. I was told holley jets and demon jets were the same.

I bumped the primary jetting down from 86 to 82, then I bumped the secondary jetting up from 92 to 94.

I let motor heat up to normal temp and then played with 4 idle mixture screws. The best AFR i could get was 12.9-13.1 and that was with the 4 screws 7/8" turn out. Vac was 11in HG and idle was 850rpm. If I turn the screws in any more the motor stalled out.

I test drove this tune and came up with this info.

idle 12.9-13.0
cruise (30-40mph) 12.5-13.0
cruise (60-70mph) 10.8-11.0 WOT 12.5
So I managed to lean up the crusie and idle a little bit but also leaned up my WOT. I noticed throttle response was lazy with 4 screws 7/8" out so I put then at 1 1/4" out and response was back to normal but my idle AFR back back to 11.8-11.9.


So I just cant get the idle to the 14.0 range, maybe I need to swap air bleeds or drill some holes in throttle blades? I was able to get cruise a little closer to the 13.5 goal but it caused my WOT to lean out to 12.5 (aiming for 11.5).

I'm wait and get fuel pressure set up correctly and then take it from there.

 

i also tried to call Barry Grant for some tech advice and found out that the company is out of business.

 

You have to drill the primary throttle blades. That gets the ratio up. You can simulate what drilling does by pulling off the larger full vac line on the side of the carb