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  Topic Review (Newest First)
09-11-2019 05:42 PM
alfaparticle Yes, it cleaned it up and therefore I should not need to swap ZT2's.

Not sure what did the trick, changing component values or running a good ground from the bar on the rear of the cam cover to the ground point for the ZT2, or a bit of both.
09-11-2019 03:54 PM
65Sprint Ed, did the new interface clean up the tach signal compared to what you had? We can still swap ZT-2s sometime.
09-11-2019 01:31 PM
alfaparticle
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.
09-10-2019 06:08 PM
alfaparticle F9's did not work well for me either. The top went lean and I could not get it back with smaller air correctors and I had to go up on main jets which made it too rich in the mid range and at part throttle.
09-10-2019 05:16 PM
gigem75 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.
09-10-2019 10:02 AM
alfaparticle 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
09-10-2019 09:56 AM
alfaparticle The signal from coil -ve is with reference to the engine because the distributor body is the ground. So in theory a connection to the block or front cover is best.
09-10-2019 09:48 AM
FlyingBanana Ed - thanks for the reply. If I take the ZT2 ground back to the battery, is that considered a good ground (from an electronics perspective)? i.e. is this likely to eliminate potential ground loops? regards
09-10-2019 07:52 AM
gigem75 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
09-10-2019 07:41 AM
alfaparticle Here is the protection circuit https://www.alfabb.com/bb/forums/car...ml#post7066409
09-10-2019 07:23 AM
alfaparticle 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.
09-10-2019 06:06 AM
65Sprint
Quote:
Originally Posted by FlyingBanana View Post
Hi. Nice stable logging output you have there! I also have a ZT2 and am really struggling to get *any* rpm signal, notwithstanding the issues discussed previously with respect to taking a noisy analogue signal from the -ve terminal of the coil....

Can I ask how you connected your ZT2 and what source you are using for the RPM input?

I contacted Zeitronix about the 99999 rpm I am currently seeing and they suggested I have a "ground loop" issue and that I should "connect the brown wire to the coil". The brown wire in their documentation is shown as the sensor ground - the RPM signal is not coming from a sensor though? Where on the coil would folks suggest I connect the brown ground wire to? Is it preferable to just connect this straight to the battery negative terminal?
I am using a Marelli-Plex ignition on the '78 Spider and use -ve on the coil for the tach input. Ed Prytherch (alfaparticle) built an interface to protect the ZT-2 from voltage spikes so the wiring for tach input is -ve on the coil to the interface, output from the interface to the green input wire for the ZT-2, and ground wire on the interface to chassis ground. All other connections are per the ZT-2 instructions with a common ground to the chassis. I don't understand the advice to connect the brown wire to the coil to solve a ground loop. Ed may be able to shine some light on this issue.
09-10-2019 04:19 AM
FlyingBanana
Stable RPM plot from ZT2

Quote:
Originally Posted by 65Sprint View Post
Hopefully it is appropriate to post some Dellorto tuning results here. If not, I trust the moderators will advise.

I have been setting up a pair of DHLA 40Ls (emissions carbs) in the '78 Spider with a modified 2L. The engine came from Ed Prytherch and is essentially the same as the first engine Ed describes in his "79 Spider on the Dyno" thread. That is, it has Venolia pistons, 10.6:1 compression, a Richard Jemison head, and Richard's 575 intake cam and 785 exhaust cam. I thought it might be useful to post the jetting specs and results and solicit comments.

The original jetting was, as far as I can determine, stock for a 2L Alfa.

148 Main Jets
57 Idle Jets
210 Air Correctors
32mm Vents
7848.3 Aux Vents
41 Pump Jets
7772.1 Emulsion Tubes
8.5g Float

After a fair amount of experimentation, the current jetting is:

140 Mains
60 Idles
195 Air Correctors.

The following graphic shows AFR by RPM in 2nd through 4th gear. These Dellortos seem to go a little rich after about 5700 rpm. Larger air correctors can keep the AFR in an acceptable range but if too large, the AFRs are too lean around 5400. Of course a larger main jet can be used along with larger air correctors but the same "rich" trend occurs at slightly different engine speeds. The current setup seems to be a reasonable compromise. Comments?
Hi. Nice stable logging output you have there! I also have a ZT2 and am really struggling to get *any* rpm signal, notwithstanding the issues discussed previously with respect to taking a noisy analogue signal from the -ve terminal of the coil....

Can I ask how you connected your ZT2 and what source you are using for the RPM input?

I contacted Zeitronix about the 99999 rpm I am currently seeing and they suggested I have a "ground loop" issue and that I should "connect the brown wire to the coil". The brown wire in their documentation is shown as the sensor ground - the RPM signal is not coming from a sensor though? Where on the coil would folks suggest I connect the brown ground wire to? Is it preferable to just connect this straight to the battery negative terminal?

At the weekend I observed 10 and 11s as the AFR when accelerating WOT in 3rd, which gradually leaned out as the rpm rose. For reference I'm using a ported 2 litre nord with stock valves, Richards cams (RJ 785 intake) and 40 DCOE 28s where the venturis have been profiled correctly and are now 33m diameter.

MJ 130
AC 180
IJ 55F8

I was running 55F9 and a 135 MJ, so switching to the combo above has given me a bit more urgency in the mid range, as I'm not running as rich. Without being able to log RPM, I'm having to glance over at the laptop every few seconds, which is sub optimal from a safety perspective, even on rural UK roads!

Thanks in advance.
09-01-2019 01:35 AM
hunttheshunt
Quote:
Originally Posted by gigem75 View Post
From reading the Weber book it appears to me the F11 tube is richer than a F9.
You're right, but F11 is more than just 1 step richer.

Order is, from rich to lean: F7 F8 F2 F11 F16 F15 F9.
08-31-2019 06:26 PM
65Sprint 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.
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