A/F mixture richness data 'on the 'road': LM1

These numbers are for comparison only, and taken with an LM-1 portable A/F meter and Bosch wide-band O2 sensor on a carburreted car.
Reference assumptions: perfect stoichiometric ratio and best emissions: A/F 14.5 or so to 1, best power: A/F 12.5 - 13.2; Over 14.5 is getting lean, and dangerous under load.

Took the car out for a drive with the new cleaned/opened out air box. Indeed, on average compared to before it was running almost 0.5 A/F or so than the stock box with the flow muffling. There is a lot of variability, and this is an approximate average. Still, it does confirm, at least for me, that opening up the stock airbox on a carb 308 should optimally have a bit richer main jetting to 135 or so.
That said, the bambino was running pretty rich before. It now cruises in the high 12s to mid 13s, and off throttle inches up to 14.1 - 14.2. Not too bad for 50 year old reliable technology, and my car is set up for power.
Any movement of the throttle opening brings in the accel pump and it temporarily richens, sometimes down to the 11s before returning to the 13s.
I reset the idle screws about 1.5 turns each and have an idle A/F of 13.5 - 14.2 depending on temp and rpm.

I do not have a good baseline for what these cars are supposed to do at tip-in (opening full throttle and accel jet discharge), but I think mine is too rich. at tip in the mixture typically initially goes into the A/F low 10s, and works it's way back into the mid 12s best power as the accel pump finishes leaving the main circuit.
I think my tip in is probably too rich - Would like to cut back on the accel pump jet, or perhaps a smaller accel pump cam. The stock accel jet is a 45 in the 40DCNF-12 and every 308 application I can find, and 40s are available. However, we were thinking about finding a set of 308 pump cams - anyone have a photo or part # of their pump cams for comparison to the very steep dash 12 version I have now?

Any experience with optimizing accel pumps gladly welcome!
best
rt

 

Figured out how to do the graph thing, and here are some photos of it installed. This is the accell pump coming in on dumping the throttle at 3000 rpm, running up to about 5500 rpm. You can then see backing off the throttle and it returning to an off throttle A/F 13 - 14. Need a smaller accel pump.
Great fun as I learn to use this thing. Will order off for the rpm sensor next and be able to plot both.
best
rt
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LM-1 provides everything. I run it from wires to the car battery, and just connect the cable to the sensor. With a 3.2, both banks dump into a single collector, so I see an aggregate of both.You can also buy other sensors, and I'm probably going to get an rpm sensor for 'on the road dyno' with WOT in 4th gear to set mixtures. It has an internal memory, so I tell it when to record, then bring it home and download into the old computer.

In a blatant departure from my usual, I only changed one thing for a second run, swapping from 140 to 135 mains (135/F24/190/53 with 34mm chokes). It cruises a bit leaner now mostly in the 13s and seems happiest at 75 - 80 mph nailing 13.8 to 14 AFR. It's amazing the variation, because in traffic you're constantly varying the butterflies for traffic and hills, and each time you open, the accel pumps fire. It's wild as you can kinda see all of that happening.
As you can see on graph 2 here, on this WOT tip in it doesn't go quite as rich, perhaps a .5 point difference, then you can see again where I back off the throttle (traffic) and then partially re-apply to accelerate.

I'm going on leave, but when I get back, will install a set of one size smaller accel pumps (140s) and see what that does.

Still got these 36mm venturis if anyone is interested!
Philip (or anyone) - would be interested in a set of 308 pump cams if someone has a set. Would be interesting to compare the 40 DCNF with your 44 DCNF cams. Also interesting is that while a 308 uses a 45 accel pump, a Ghibli V-8 uses a 40.

More as it develops
best
rt

And in the 'it makes no sense to me' category, it now idles a bit leaner in high 13s low 14s with the smaller main jets. Yes, I know it shouldn't matter. Just reporting here.
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Spoke to Mike Pierce at Pierce manifolds about tuning DCNF accelerator pumps.

In addition to the quantitative data below, the car does 'blow blue' when hitting the accel pump at idle. Mike said that it is supposed to get pretty 'fat' when the throttle is dumped, and you shouldn't neccesarily shoot for a number - it's what makes the engine happy and smooth without stumbling.

This backs up advice FChat Aces Philip Airey and Mark Eberhardt sent me as well. In short, the A/F 10 - 11 is fine as long as it is a smooth transition. Also important is the over run when throttle is closed to prevent the plugs loading up. Mine will jump to 14 - 15.5 when it comes off throttle closed and Mike said that sounded about right. He said that it might be worth trying a 40 to see if it would still be smooth with a smaller pump shot to get the A/F a bit more in the power range. He also stated that sizes in accell pumps typically did make a pretty noticible change. A set of 40s should be here in 7 days.

So, it seems like a maxim in tuning Webers be it main jetting or accel pumps, is to start rich and back off to where the car is 'happy'.

Any advice or other experiences welcome!
best
rt

 

Coincidentally, there was just an episode of 'Two Guys Garage' with a computer wideband A/F meter. Watching their tracing of a dyno run on a new fuel injected Ford (?), upon throttle application the injection computer sent the A/F down to around 10-11 as well and held it during WOT, while off throttle going up to 16, and cruising mid/high 14s. Mid throttle application looked to give 12-13s.
If anyone got a better view, please correct me.

As Philip has said, Ferrari K-jet dyno A/Fs I have seen track right at A/F 14 like a rail with little variations in every regime. Perfect for best emissions.

Will post the results of the new 40 accell jets (down from stock 45) in a couple of weeks