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
7848.3 Aux Vents
41 Pump Jets
7772.1 Emulsion Tubes
After a fair amount of experimentation, the current jetting is:
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.
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.