M758

I know you can adjust something in the stock barn door air flow meter to adjust air fuel ratio. What is it?

Anyone have the details.

It seem like the FR wilk DME site is down?

Thanks

M758

Ok,
Found some info on FR Wilk Site.

Here is a picture of the AFM numbered.

Last time out my spec car was running a bit rich. I will be taking it to a dyno Saturday. My plan is to test the A/F Ratio and if it is off try to adjust it back in.

What is adjustment "****" and which way for lean vs richer?

Looking through search still has be a bit lost on this.

Sam Lin

The little adjustor screw is accessed through the tiny round plug covering it, which is accessible from outside the entire unit (don't have to open it up like the pic). I'm not sure which direction does what on it.

I have a wideband if you would like to use it.

Sam

Flight_951

Right=rich Left=lean

Flight_951

I should mention the tool of choice in the late models is a 6 point 3mm hex key. I was able to get mine pretty good using the a/f ratio gauge and seat of the pants improvement (plus I knew it was too rich initially). Just a half turn did it. I'll get it sampled in the next couple weeks.

dgz924s

Joe
Look on the AFM body right at the hose connection you will see a 1/2 round hole with a cap or without. If without you will see a 8/12pt set screw deep in the hole. This is the adjustment screw for the A/F-O2. This is usually adjusted with a exhaust tester to ensure you are getting the proper setting/mixture. Really no way to see a difference "tuning by ear". May see the thing lean out but how far is crucial.

Flight_951

My Bosch replacement unit used a 3mm 6 point, confirmed when I spoke to Bosch by phone.

dgz924s

Could be 6pt. I don't recall really but thats easy enough to figure out anyway.

M758

Guys,
From the research I believe I am running fine at idle, but rich at full throttle. As I understand the screw only impacts the idle behavior. I care about WOT where the car spends most of it's time. I had the unit adjust a couple years ago before I added the chip and the hole you are talking about was never touched. The black cover was removed and it A/F ratio at that time was noticely tweaked for the better. I want to do that again, but don't know what to turn. My tuner moved to colorado so he can't adjust for me.

Flight_951

The black cover really shouldn't be removed. It's calibrated by Bosch. Maybe the tech adjusted the wiper arms in the AFM to get a better track on the strips?

dgz924s

Yep that what it sounds liike. The only adjustment to do there, the spring assembly should never be touched. To adjust the mixture it is done by turning the set screw CCW for lean. If you are going to the dyno this is a good time to adjust correctly in all RPM ranges. Remember you are dealing with percentage values here not seat of the pants feel or it looks right. Last thing you want to do is run it too lean and this can happen by not getting a test value result. You race the car and you sure don't want to be real lean with an engine under the pressure during racing and somewhere in the rpm range burn a hole in a piston. Not that it cant happen under street driving.

Danno

"From the research I believe I am running fine at idle, but rich at full throttle. As I understand the screw only impacts the idle behavior."

Yeah, the external adjuster screw is to bypass air around the flapper-door and affects mainly idle mixtures. You can make across-the-board adjustments with the FQS switch...

M758

He did not do that. I did that adjustment later on after I had some other issues.

Danno...
... So the FQS impacts mixture? I though it was for timing adjustments only. IE advnace and retard and 99% of the time it was already optimal. Changes such if the fuel was not to standard one could still run albiet at a lower power level.

Never heard of the FQS impacting lean/rich.

Danno

"Never heard of the FQS impacting lean/rich."

Check out the FQS table on my 951 RacerX website. You can make +/- 3% and +6% fuel changes with the FQS switch, along with a 2.7-degree retard if needed. I can also program in any fuel-adjustment and ignition-changes you want into the FQS switch. Paul Bloomberg out in your area tested several versions of my NA chips along with the FR Wilk one. You can ask him about the results.

M758

Danno,
so if the FQS is in the stock position and the car runs a bit rich. Adjusting to position 2 should take away a bit of fuel. Dyno again to check the result.

How does adjusting spring tension impact fuel mixture. Can I get more than 3.1% reduction if needed?

I know Paul tested a bunch of chips and settings. No real power gains anywhere. I am currently running one of his cast off's. I think it is a Steve R unit. Anyway back when I installed it my car did not seem to make much of a power gain. Maybe 2-3 hp. Now I still use it as 2-3 while small is valuable. I it was running rich with the 88 pistons and block (still had the 87 924S head and cam on it). It seemed to be fine when I had it using the 84 block.

Would a change in compression ratio from 9.5:1 to 10.2:1 require a change in mixture?

I had to switch to the 84 block after the 88 one spun a bearing. In time I plan to go back to the 88 block for the high compression ratio. I did a back to back test using the stock 88 DME and 87 DME with the Steve R chip. I seemed like the chipped DME make the engine a bit more lively. I never had the chance to dyno check it however.

So now with 84 block in the car I have chance to dyno it and might as well prepare for a possible rich mixture. If see it I want to be able to get it right.

EDIT...
For those confused when I say 88 block I mean 88 block and pistons (10.2:1). When I say 84 block I mean 84 block and pistons (9.5:1). I really like to keep the pistons in their original blocks with their crankshafts too. Seems more natural too me. Sorry for any confusion.