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]

Ansbacher, thanks. I'm going through this now with my lightly-warmed-over race car (light cams, little more compression). What's your engine build specs?

I'll post my specs later tonight when I can get to my notes, but I'm running pretty fat all around: 11AFR at idle and light throttle, and 11.8-12.1 at full throttle from 4k-6.5k. I'm running 34mm venturis.

[MarkV]

My car is a 2056 with a little over 9:1 compression ratio and I am at 2200 ft above sea level with Delloroto DRLA 40's.

60 Idles
132 Mains
34 Vents
180 Air

When I bought the car the previous owner had it set up all wrong....it had.

65 Idles
122 Mains
28 Vents
195 Air

[GregAmy]

What AFRs are you guys getting with these setups? If not measuring, what outputs (feel, mileage, drivability, etc) are you using to gauge success?

[MarkV]

I have not checked the AFR...I suspect it is a little on the rich side. Before I put classic car insurance on it I had to pass emissions and it was always difficult to get the HC number low enough to pass. I am going by the plug and tail pipe color...both of which look good. The cylinder head temperature seems to stay around 275 in town. I frequent a mountain road that goes from about 3000 ft to about 8500 ft. and if I am pushing it in the summer the temperature can get to 350 degrees. Gas mileage is not great...maybe 20 MPG. The car runs well and doesn't really have any drive ability issues. There was an off the line stumble that took me a long time to figure out that turned out to be the ignition timing curve and not carb related.

[anderssj]

My dells are set up with 30mm main venturis, 55 idle jets, 135 main jets, 180 air correction jets, and 9164.2 emulsion tubes. I know some of these are a little smaller than the factory settings, but they seem to work well with the current engine (1973 2.0L, Elgin 7008-4 cam [280* duration, .332 lobe lift], Mahle Euro PC set [8.0:1]). The car runs really well (maybe a little bit rich judging by color of spark plugs and exhaust). This set-up used to pass WA State emissions tests back when I lived in Redmond . . . .

[Ansbacher]

The guy that rebuilt my engine passed on before I purchased the car and he left no records of the specs he rebuilt it to, therefore I have no idea of the final displacement or what cam is running. My analysis as to how it runs is strictly seat of the pants - it idles great, accelerates strong, no bog starting out, no flat spots higher up, and the plugs indicate a properly tuned engine, and all this with an 009 distributor! I would love to convert to a vacuum dizzy but only the left carb is tapped for ported vacuum and apparently both are needed when using DRLAs and a vacuum setup.

Ansbacher

[rhodyguy]

Good setup if it could fool the sniffers in WA.

[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.

[anderssj]

Good setup if it could fool the sniffers in WA.

. . . and could peg the 120 mph speedo just before the kink at the end of the straight at Seattle International Raceway (IMG:style_emoticons/default/biggrin.gif)