My Dellorto Jet Combination Options

[Ansbacher]

I know every carb/engine combo is different, but for those of you with dual Dellorto DRLA 40s I thought I'd share a jet combo that finally performs very well on my '74 2.0 Liter. Note, I am basically at sea level here in the Tampa Bay area:

60 Idles
150 Mains
180 Airs
40 Pumps
Emulsion Tube .2
32 Vents
Pump Adjustment Nut almost all the way in.

Maybe this will help someone with a starting point. Took me a couple of years to finally get this right.


Ansbacher

[GregAmy]

Well, OK, I was hoping someone had AFRs for comparison...I started with:

34mm venturis
60 idle jets
140 main jets
180 air correction tubes
35 accel pump jets
#2 emulsion tube
Pump adjustment nut set to book specs

Note that this is the factory calibration for an out-of-the-box 40 DRLA. We found during some light-to-spirited street driving, that the car was lean down low and running fat up top. I got the oil temps up to 190 but no CHT. Started fine, idled and ran fine, but 15-16s at idle and light throttle, and fat full-throttle (12-13). I also noticed a hesitation and a full-lean AFR jump during throttle transition to full-throttle.

For last weekend's race we swapped to 70 idle jets and 55 accel pump jets (I don't have any mains). At Lime Rock last weekend, very warm and humid, it's now idling and light throttle fat, in the 11s, and we're seeing strong 11.9-12.3 AFRs full throttle from 4000-6500 RPM. I did notice during the warm-up laps that I had a undesireable "flutter" and jump to lean during quicker transitions to full throttle. Of course, during the races I'm not very concerned about that transition and didin't notice anything significant.

We pulled the plugs and found them to be really nice, that desired light tan in color with no evidence of fouling.

For reference, this is a Foley-built engine with warmed-over cams, slight overbore, a bit more compression, but otherwise a generally stock build. Wideband sensor is located just downstream of the collector; we're using a prior-gen Tangerine header.

The condition of the plugs make me think we should just leave it alone, but I may try to tune out some of that fuel up top just to see a bit more ponies. I also may dink around with the pump adjustment to clean up that flutter. I've got some 2.00 air correction tubes we can play with, along with Jet Doctors I've yet to install (should lean out idle and light throttle). If anyone has any #1 or #3 tubes hanging around I may test that as well.

If you guys are running smaller venturis and comparable or larger idles and/or mains, you're probably running pretty fat...

I also have some 170 and 180 mains available for sale/trade if anyone needs to go that far.