Adjusting "Verboten" screw

[bnam]

I installed a W02 sensor and logging capable controller (LM02) on my 74Tii yesterday and after some initial issues (I did not calibrate it even though I thought I did), I got it working and it shows me that the car is running pretty lean.

Once I attached the RPM sensor, I will log my readings.

The car came with a 292cam, so I know I will not get it "proper", but wondering if there were suggestions on what reasonable compromise would be.

Byas

[bnam]

My first set of readings:

900 (idle) -- 12.2

1000 -- 11.7

1500* -- 13.0

2000 -- 14.0

2500 -- 16.1

3000 -- 16.1

Since most of my driving is in the 2000-3500 range, should I try to get it richer there? and live with it being over rich in the lower down? I'm assuming I can get idle back closer to about 13 with the screw once I've set the general enrichment.

This is my first time attempting this, so would appreciate any guidance and constructive criticism.

Thx!

Byas

[MAD02]

My first set of readings:

900 (idle) -- 12.2

1000 -- 11.7

1500* -- 13.0

2000 -- 14.0

2500 -- 16.1

3000 -- 16.1

Since most of my driving is in the 2000-3500 range, should I try to get it richer there? and live with it being over rich in the lower down? I'm assuming I can get idle back closer to about 13 with the screw once I've set the general enrichment.

This is my first time attempting this, so would appreciate any guidance and constructive criticism.

Thx!

Byas

The proper air/fuel ratio for a NA car would be about 13.5 under load. Turbo cars would need 12.5 or lower under load. If your running a 16 A/F ratio under load that is way to lean and could cause your engine to knock (detonation). I don't have a Tii, but maybe the cam has something to do with the car running lean??

[dubois]

My first set of readings:

900 (idle) -- 12.2

1000 -- 11.7

1500* -- 13.0

2000 -- 14.0

2500 -- 16.1

3000 -- 16.1

Since most of my driving is in the 2000-3500 range, should I try to get it richer there? and live with it being over rich in the lower down? I'm assuming I can get idle back closer to about 13 with the screw once I've set the general enrichment.

This is my first time attempting this, so would appreciate any guidance and constructive criticism.

Thx!

Byas

16.1 is definitely way too lean, anything between 12.5 and 13.5 is good. With the 292 the idea is to rev higher around 4 and 5 k rpm. If your driving is below that, I would suggest a stock cam 264, you will get more torque. In the mean time enrich your mix.

[bnam]

Agree it's way too lean. Car came with the cam. Plus not sure if the screw had been futzed with.

Adjusted it a bit and got the following result.

900 - 12.3 (no significant change)

1000 -- 11.3

1500* -- 13.7 (est)

2000 -- 12.7

2500 -- 14.5

3000 -- 14.9

Down. But still too lean. Too late to try another round today.

BTW, I had a problem with getting a reading at 1500 rpm. I could not hold it at 1500. I can get to about 1350, but if I push slightly beyond that, it revs up to 17-1800. Same while going down from 1700. It's way too sensitive in that range.

Is this common for Tiis or unique to my car? Can anyone else hold 1500 on their Tii?

One more question -- these readings are with the car stationary and revved up -- i.e. no load. Is this a factor one way or another?

Thx!

Byas

[C02]

Load is important. 2K rpm stationary has different fuel requirements than 2K with the pedal mashed at a freeway onramp. You'll want to use you LM2 to collect data as you drive your 02 around in real world load/power requirements. The lm2 will let you see 3D maps of your A/F ratios as a surface map. I did this a while back on a fuel injected Ducati. WB02 is a great tuning tool.

[c.d.iesel]

yea - what CO2-in-LA said -

you do these readings while the car is under load - driving down the road,

not sitting still free reving!

and you also need a reading at FULL THROTTLE,

while up hill pulling,

in 3rd gear

while sustaining 4,000 rpm

(you may use 2nd gear as you need

a lot of long up hill grade with 3rd gear speeds)

this is dyno testing on a real road

Repeat these load readings and then your doing something

Be consistant every time you take readings duplicating the same conditions.

[bnam]

Got it. Luckily I live on the top of a hill so can do a 2nd gear 4K runs on the road that runs by my house and loops back down the hill. Will try this evening.

Byas

[c.d.iesel]

here's what your looking for:

idle approx 1.5 .....2.0% CO (AFR 13.94 ....13.77)

partial throttle approx 3.5% CO (AFR 13.20)

full throttle approx 5.0% CO (AFR 12.64)

idle is with oil and coolent at full operating temp

partial throttle is approx 1/4 to 1/3 throttle opening

at a rpm like 2,000 - cruising , not pulling hard

You use a VACUUM for consistant repeatible

testing. The vacuum gauge will read approx 19 in which tells

you your holding the throttle at the same opening with each test run.

So every run you start with your PARTIAL THROTTLE held

at the same vacuum reading and approx MPH for 2nd or 3rd gear

untill you have a stable reading. Then you increase to your

FULL THROTTLE pull up the long hill - maintaining FULL OPEN

for at least 5 - 10 seconds for a stable reading.

Your ignition timing should be adjusted with a timing light and

not touched again. "BALL" mark in inspection hole @ 2,500 rpm

give us your readings and then the discussion about how to adjust

comes later

[bnam]

I have a new(ish) (002 I believe) centrifugal only Tii distributor that came with the car. However, I had noticed that it puts out more advance than stock. I could not do the 2500rpm "ball" timing -- fuel return hose and Airbox back nozzle were in the way, but did 2500 timing using the front mark and adjustable light. However, this then gave me couple of degrees of retard at idle. So now timed to be 6deg advance at idle. My estimate is that this results in ~32deg @2500 vs. the 27deg spec.

What is the impact of this timing on the mixture - if any?

I did acquire a used original 74Tii distributor. I can swap it in and see if it has a better curve.

Driving to work this morning fully warmed up pulling uphill 3000rpm in 4th, the reading was 15.x. Cruising part throttle flat road at 65 in 5th, the readings were 14.8-15.2.

I'll need to find a long uphill to go full throttle -- there's a 25mph speed limit on the one on which we live.

Byas

[bnam]

Driving back home -- readings were still 14. to 16 throughout. Felt too high.

WOT on 4th uphill doing about 70 on HYWY 50 it was 15.8

When I got home, I turned the screw in 1/4 turn then drove to get some gas. A new problem cropped up -- car would not return to idle quickly -- took a while.

I suspected an airleak -- 3 suspects behind the throttle were the hose from the warm up regulator to throttle body and the 2 hoses that go to the deceleration valve (74Tii only). I clamped the larger of the latter 2 and the revs immediately died down. Looks like a failed valve. Once clamped, the AFR ratios were much lower. The no-load readings at the above RPMs were all around 11-12.

I'll cap off both the valve hoses, and check the AFR readings with load tomorrow.

Byas

[bnam]

Got my LM02 data logging working properly -- had a faulty USB cable.

Idle setting adjusted to about 2.4-2.5% CO

[bnam]

here's what your looking for:

idle approx 1.5 .....2.0% CO (AFR 13.94 ....13.77)

partial throttle approx 3.5% CO (AFR 13.20)

full throttle approx 5.0% CO (AFR 12.64)

idle is with oil and coolent at full operating temp

partial throttle is approx 1/4 to 1/3 throttle opening

at a rpm like 2,000 - cruising , not pulling hard

You use a VACUUM for consistant repeatible

testing. The vacuum gauge will read approx 19 in which tells

you your holding the throttle at the same opening with each test run.

So every run you start with your PARTIAL THROTTLE held

at the same vacuum reading and approx MPH for 2nd or 3rd gear

untill you have a stable reading. Then you increase to your

FULL THROTTLE pull up the long hill - maintaining FULL OPEN

for at least 5 - 10 seconds for a stable reading.

Your ignition timing should be adjusted with a timing light and

not touched again. "BALL" mark in inspection hole @ 2,500 rpm

give us your readings and then the discussion about how to adjust

comes later

Ignition -- set @ 4deg at idle & 27deg at 2700rpm (spec is 25deg at 2700rpm) with the ball (managed to hook up some wires to pull the return hose out of the way, but ended up burning the pick up of my tack so could not adjust closer, but this is close enough, right?)

Idle -- hot reading, (oil, water all hot) -- 13.2 @ 900 (can try to get this closer).

Full throttle uphill in 4th @ 3500 rpm --> 13.9 to 14.1 (2 runs)

Full throttle uphill in 4th @ 2200 rpm --> 13.2 (1 run only and shorter than the other)

Partial throttle readings between 12.7 and 15.8 -- I need to take a 1/3 to 1/4 reading. Will update with that.

Byas

[cxzsaq]

I installed a W02 sensor and logging capable controller (LM02) on my 74Tii yesterday...

Hey. Quick question. Can you kindly described your sensor/controller setup? I have a wideband afr see sorry but it's just hooked up to guage and I'd like to have mine record more info, like rpms. How do you have the rpms readings taken? Thank you.

[bnam]

I installed a W02 sensor and logging capable controller (LM02) on my 74Tii yesterday...

Hey. Quick question. Can you kindly described your sensor/controller setup? I have a wideband afr see sorry but it's just hooked up to guage and I'd like to have mine record more info, like rpms. How do you have the rpms readings taken? Thank you.

I have this device LM02 instead of a gauge. I've also hooked up a connection from the tach for rpm (actually from the the test plug in the engine bay). I also have a manifold vacuum sensor which I've not hooked up yet. The LM02 lets you log multiple inputs at the same time. you ca record on SD card or direct to PC (see earlier pic of a screen shot).