Alfa Romeo Forums banner

Weber tuning with Lambda sensor

86K views 233 replies 21 participants last post by  TannerTrent 
#1 · (Edited)
Hi BB,

I am running a pair of Italian 45DCOE9's on my hot little 2L and to aid in tuning I recently purchased an AEM "UEGO" lambda sensor setup which consists of a Air/Fuel ratio gauge with digital readout, a calibrated Oxygen sensor, and all the mounts/wiring/etc needed to hook it up. I had already welded a bung for an 02 sensor when I had first got my car running, so it was a fairly easy affair to get this thing up and reading. I choose to get this tuning aid to assist me with my limited Weber tuning experience.

Long ago I learned in school that the ideal air/fuel mixture is 14.7:1. Does this mean that my car will always run better at this ratio? I ask because I had to really alter my main jet size to even start getting close to this ratio. Above 3K RPM, running on my 155 main jets, I was getting a air/fuel ratio of about 10.0:1 (way rich)! I installed the smallest main jets I had in my box (135) and I am now getting an air/fuel ratio of about 12.5:1 and the car definitely pulls harder and cleaner. I have to place an order for even smaller jets to try and get me towards the 14.7 ratio but I am being cautious because I don't want to blow up this engine with a overly lean mixture. I guess my question is: SHALL I CONTINUE TO GO LEAN? I am running RJ cams, 85mm pistons, Sperry stage 5 head with big valves, etc. I thought I'd have a thirstier engine than this!

All the above is in regards to the MAIN circuit, but my car is also running quite rich on the idle circuits. I have a pretty good selection of idle jets and was able to go from a 60F8 to a 50F8, however unlike the main circuit which took well to the change from large-to-small jet, my engine did not like the leaner idle jet, it starting popping severely off idle, yet still reading quite rich on the Air/Fuel gauge......confused......should an engine always run better at 14.7 or do some engine just want a richer mixture?
 
See less See more
#158 · (Edited)
I would go a little larger on the air correctors. It should not be a problem if AFR hits 13.5 at 5200 so long as it gradually lowers towards peak HP rpm, probably around 6200. Then do a test run, print out the logged curve and draw a horizontal line at 12.8 AFR. Is there more area above or below the curve. If above then go back down on the AC's.

I am jealous of your nice clean rpm signal and I wonder if there is a problem with my Zeitronix ZT2. Maybe we could put my box in your car and see if the rpm log is still clean?
 
#159 ·
Thanks Ed. I have a log using 210 ACs giving maximum AFRs of 13.3 between 5200 and 5600 rpm. The thought was to keep things just a smidgen rich but sounds like that is not necessary. I will compare areas above and below 12.8.

We can certainly swap your Zeitronix and see if there is a difference.
 
#160 · (Edited)
Here are a couple of graphics showing logged AFR curves in reference to a horizontal line drawn at 12.8:1. The first curve was captured while using 195 air correctors and the second was captured using 210s. Looking at the acceleration runs for third gear (in the middle of the graphs) and ignoring the initial variability after the shift, the area below the reference line is clearly greater than the area above the line using the 195 ACs. Using 210 ACs, the areas above and below the reference line even out slightly, which confirms Ed's advice above.
 

Attachments

#161 · (Edited)
I would use the 195's because of the rising AFR at high rpm with the 210's in 4th gear. My tests have always been up to about 7000 rpm and I have always seen a falling AFR above peak HP with Webers with reasonably correct jetting.

It is interesting that you are much leaner in 4th gear than in 3rd. I have seen that but not as pronounced and it is the reason that I after doing a lot of tuning runs in 3rd gear I do one in 4th to make sure that I do not have a high rpm lean situation. Are you using a high capacity fuel pump and regulator?
 
#163 · (Edited)
The shape of the curve with the 210s mimics the shape of the curve with the 195s. The second (210) graph above is misleading for the fourth gear run as I had to let off at about 5600. If the run had continued, the slope would have become negative above 5700 or so.

My tests have always been up to about 7000 rpm and I have always seen a falling AFR above peak HP with Webers with reasonably correct jetting.
Good to know that the behavior of the Dellortos is similar to Webers. Maybe this engine with 32mm venturis and small exhaust makes peak HP around 5600? Lower than I expected, if that is the case.

It is interesting that you are much leaner in 4th gear than in 3rd. I have seen that but not as pronounced and it is the reason that I after doing a lot of tuning runs in 3rd gear I do one in 4th to make sure that I do not have a high rpm lean situation. Are you using a high capacity fuel pump and regulator?
The curves in fourth gear are certainly flatter than third. A possible, partial explanation is that I have not be able to run the engine to 6500+ in fourth. I expect the AFR would continue to decrease at engine speeds above 6200.

The pump is rated for 30 gph. I confirmed fuel volume output when it was installed two years ago. Last week, the rear fuel filter and the front filter-regulator were replaced to address an intermittent fuel starvation issue. The new filter-regulator is a Filter King with the 67mm bowl and is set for 3psi. There have been no starvation symptoms since those changes however it has not been 95 degrees over the past several days so vapor lock is still a possibility. I don't think fuel delivery issues are currently impacting AFRs.
 
#165 ·
Hope it's ok if I join in....
I can't log data but I can get it. I recorded my screen of the 123 during my runs and recorded the afr's with a tach. Pretty southern but cheaper than a laptop.
At 6500 in 3rd I have 13.7 which is lean obviously and the advance is 37 degrees. If I backed it off to 35 which I think I should do anyway will that change the afr numbers? !'m running 135 mains, 50f8 idle, and 210 AC.
200s are going in next and back off the timing to 35. Thoughts? Thanks
 
#167 ·
Thanks Ed, always nice to have confirmation. I did back off to 35 max and brought it in with 26@3000, 33@4000, and 35@4500. The 200's done good.
4th gear cruise 12.8@4200 cruise
3rd gear 12.8@6500
2nd gear 12.6@6600
3rd gear progression
11.1@4600
11.3@5000
12.5@5300
12.8@6400
Not as good as logging but stepping frame by frame in my editing program got me there. Now only if the guys at 123 or the afr folks would BlueTooth all this data and bring it into one unit we'd be sitting pretty. btw I got 10 Fine-Thread 18-8 Stainless Steel Thin Hex Nut, M10 x 1 mm Thread from McMaster for the windage tray and they worked great in lieu of the pal nuts on the main caps. Also got longer 7mm bolts for the oilpan to make up for the thickness of the tray and extra gasket. You saved me on that.
 
#169 ·
I did not measure the CR and have not done a compression check. I did take a sample of my first oil at 1000 miles and send it to Blackstone Labs for analysis. Mainly to check for the absence of any bronze from the oil pump drive gear. I'll post the results when I get them.
 
#171 ·
Thanks, I appreciate.
When I did those last runs yesterday afternoon it was 95 degrees. We had a mini front move through last night which brought lower temps. Normally the lows are 78 with high humidity. This morning it's 75 and low humidity. Really nice actually! I just got back from a couple of runs and got some 13s up top. I don't know if the temp had anything to do with it but I wanted to double check my numbers from yesterday. I'm glad I did.
As it stands now I'm at:
DCOE 32s
34 venturis
50f8 idle
f11 tubes
135 mains
200 ac
I'm not sure if I have any 195 ACs. If I do I'll try them first then go with a 140 main jet. 140 seems awful big though.
 
#172 ·
AFRs

At 6500 in 3rd I have 13.7 which is lean obviously and the advance is 37 degrees.
Actually 13.7 isn`t a "lean" mixture as such. 13- 13.8 is my target in the race cars for power.

I would attempt to lean the 11s a bit to get over the rich range for better power.

Typically your cruise AFRs should be in the mid 13s to 14. And idle (no load) is rich. Have you tried closing the idle mixture screws a quarter or half turn.

145 F8 idle jets?? Never had such small idle jets work in any Alfa.
 
#173 ·
Thanks Richard. I'm since gone to 50f8 idle jets and adjusted for high 12s to 13 at idle. With the temp being 75 this morning as opposed to 95 yesterday in third gear @ 6300 the afr is 13.2
From reading the Weber book it appears to me the F11 tube is richer than a F9. fewer holes and smaller diameter, less air more fuel=richer. IF I'm reading correctly. So I'll stay with the F11.
 
#174 ·
Thanks for the specs. Your ambient temperatures are very similar to mine. I am going to hold the current setup static for now but may try 34mm venturis in a few months.

At 3000 rpm in fifth gear, part throttle, AFRs are in the high 14s to mid 15s. At 4000 rpm in fifth, part throttle, the AFRs are in the mid 14s. Suspect there will be some jetting changes required after the temperatures cool down.
 
#178 ·
I spoke with Mark Robinson yesterday and he is also using the same interface circuit with a Pertronix distributor and a ZT2 and he has good rpm plots. I think that I posted the circuit on the ABB.
Make sure that the ground wire to the ZT2 is a very good one. "ground loops" are often associated with high resistance in that circuit.
 
#180 ·
Thank you Mr. Hunt. I guess that keeping out of the 13s AFR @wot with an F11, 135 mains, and 34 venturis means my headwork must be doing something right. btw I ran a compression check yesterday and got 195 psi +- 5 psi on all four. I don't recall exactly without looking it up but my LCs are 104 on each cam. 472 intake and 785 exhaust.
I don't know if anyone has used the Track Addict app but it is pretty slick. It gives you 0-60 times, 1/8th, 1/4 mile times in the drag mode and in the track mode it records times, accel, braking, etc. I'd been using the free version and just plunked down my $8.99 for the pro version so I can record more than three sessions. I got a 5.3 second 0-60 time in my Giulia and I'll give the GTV a try next. finger's crossed :)
 
#183 ·
Mike,
I looked at the Weber drawings for emulsion tubes and F16 and F11 are almost identical except that F11 has 4 extra high holes which I think are intended to lean the mixture a little at high rpm.
John Passini wrote that nearly all Ford engines with DCOE's use either F16 or F11. F16 being the choice for full blown race engines and F11 for "less hairy" motors.
In my case it is mid range richness that I would like to lessen when the top end is tuned for 12.8 to 13.2
 
#184 ·
Ed, I have a set of F9s. If I remember correctly I had them in but changed to the F11s because a sputter or bumble at steady rpms without any load. It was so long ago before I had the wide band. It's a totally different motor now and since I have the wide band it can't hurt to drop some F9s in to see what happens.
When I pulled the plugs to do the compression check the insulators were white white but with no deposits and the outer base was black. I'd like to see a light chocolate brown on the insulators and base.
 
#186 ·
Interface circuit

I built another of the little interface circuits today and played around with it on the bench. The capacitor should be 10 nF and the resistors should be 22K for best results. I hooked it up to the coil -ve and I got a pretty clean rpm trace up to 7000 rpm.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top