Alfa Romeo Forums banner

1 - 20 of 28 Posts

·
Registered
Joined
·
11 Posts
Discussion Starter #1
I have a '76 Alfetta GT 2L that I have converted to Dellorto carburetors. It also has exhaust headers and a 123 Ignition. Performance is not good at lower rpm when I'm in traffic. I want to change out the spica cams to something better. I have some 10548 cams that I intend on using (being worn out is an unknown). Some comments have been made regarding use of these cams only on the intake side.
I would like to know if I am on the correct path. What is the cam timing supposed to be? Most of the comments are over my head when it come to lash, duration, and overlap.

On a different thought.
Can you retro-fit paddle shifters to a 2017 Alfa? Is the wiring loom in the steering column ready for it?
 

·
Premium Member
Joined
·
13,688 Posts
Not good at lower rpm sounds like the carbs need setting up properly. 10548's will be an improvement but don't expect anything profound, Lobe centers of 104/104 with standard lash.
 

·
Premium Member
Joined
·
21,455 Posts
Have you checked the basics like timing and jetting? Too lean and not enough advance will make it sluggish down low.
Andrew
 

·
Registered
Joined
·
1,267 Posts
This^^. Timed it at "massimo" and observed the advancing?
 

·
Registered
Joined
·
11 Posts
Discussion Starter #5
Thanks for the feed back. The 123 Ignition is set a 20 degrees @ 1500 rpm. That was the preset at the time of purchase. That timing was supposed to be for a spica injected system and I don't know where to go from there. The Dellortos have the jetting as described in a Haynes manual for '73-'80 Alfa Romeo page 64. Maybe I'll push the advance up to 22 or something. I had a richer set of jets in it and the plugs were black so I went with the Haynes book. To me it kinda drives like a two cycle dirt bike of the '70's... you had to keep 'em in the power band to get any speed out of them.
 

·
But Mad North-Northwest
Joined
·
10,205 Posts
Which Dellortos do you have? The jetting can be very different depending on the model: what letter do you have after the 40? I've got various Alfa jetting tables around here somewhere.

Also do the basic stuff like verifying fuel pressure. More than 3 PSI you're gonna be rich and it'll run crappy.
 

·
Registered
Joined
·
11 Posts
Discussion Starter #8
Thanks for the comments. The Dellorto's metal tag says "5371P 0605346260 ". I see no other numbers an the carbs. As I recall, the fuel pump was for an Alfa conversion and had a max pressure of 6 pounds. Redline was the provider I think. I have put the jets in as described in Haynes manual '73-'80 Alfa Romeo pg 64. I had a richer set of jets in and the plugs were black so I went with Haynes. The 123 ignition is set at 20 degrees @ 1500 rpm. That was the preset at the time of purchase and it was for a spica injected system. The car runs like a '70's dirt bike. If your not in the power band, then it will lode up. I check the fuel pressure.
 

·
Registered
Joined
·
11 Posts
Discussion Starter #9
Based on the Advance curve form the provider... I timed it at Point 3= 1500 rpm 20 degrees. Then the graph shows Point 4 as 3000 rpm 34 degrees and Point 5 as 4200 rpm 37 degrees. I have not checked the advance beyond Point 3.
 

·
But Mad North-Northwest
Joined
·
10,205 Posts
1) You almost certainly need a fuel pressure regulator if you don't have one
2) Check the body of the carb. Where it says 40 DHLA is there a letter after that?
3) If you have a programmable 123, the below from Tom Sahines is a good starting curve to set. If you have the one with the rotating switch I can't help you

RPM LIMIT 6500 (or less if you are concerned about over revving your motor)
point 1 500 rpm 6 degrees
point 2 1000 - 6
point 3 2000 - 20
point 4 4500 - 38 (I use 36 here)
point 5 8000 - 38 (I use 36 here)
 

·
Registered
Joined
·
11 Posts
Discussion Starter #11
DLHA 40 L I'll change the the rev curve. Never done it, but now is the time.. .after the pressure regulator is in. Thanks
 

·
But Mad North-Northwest
Joined
·
10,205 Posts
The DHLA L is a later emissions Dellorto which is actually a good thing for a street car: they're actually a lot more sophisticated than the earlier carbs, have good drivability, and can be easier to tune. That said, the jetting is very different from a standard DHLA and if you use the standard jetting No Workie Good. These have a fixed air calibration hole and need different idle jets and markedly different emulsion tubes.

I dunno what type of car the 5371 reference is for, but I don't believe it's an Alfa. That said, the 40L was used on the Alfetta 2.0 and here's the jetting I found for it.

I can't guarantee how well this'll work, but my 2L GTV has similar 40G carbs, is jetted to the book, and runs well. But first make sure you're not exceeding 3 psi at the carbs, and if you are add a regulator.

1618602



1618603
 

·
Registered
Joined
·
11 Posts
Discussion Starter #13
Thanks for the jetting chart.... I had a Redline pressure reducing valve and checked it with a 10psi gauge. It read 3psi.
 

·
But Mad North-Northwest
Joined
·
10,205 Posts
That sounds good. Now check your jetting and see how it compares to the table above.

On the emissions Dellortos like the 40L the idle jet draws from the main jet stack rather than the fuel bowl. It's designed so that once the main jet starts aerating, the idle jet cuts off. This is pretty neat, as it avoids the need to tune the transition like you do on Webers. For this to work, however, you need specific aux venturis, main emulsion tubes, and idle jets. See the second post in this thread for some details:

 

·
Registered
Joined
·
11 Posts
Discussion Starter #15
As luck would have it, the Dellortos came from Italy with the correct jets. I re-jetted them from the Haynes manual. That was wrong, I guess. The exploded view if the Dellorto carb did not identify the "idle air metering" but since the rest of the jetting is correct, I'll let that go.
 

·
But Mad North-Northwest
Joined
·
10,205 Posts
Yeah, if you use non-emissions jetting with an emissions Dellorto it won't run right.

The idle air metering on the 40L is fixed at 2.2mm (that's the 220 in the table, the little circle means "fixed".) That's why the emissions Dellortos use specific idle jet holders that don't have an air calibration hole. Should look like the one at the link:

 

·
But Mad North-Northwest
Joined
·
10,205 Posts
Here's the regular idle jet holder. Note the second hole in the bottom half.

 

·
Registered
Joined
·
11 Posts
Discussion Starter #18
Now that I know where it is, it has no number and only the upper holes. So it's the non emissions from what I understand. Haynes manual calls it a jet carrier. The no number part of this threw me. Has the 57 jet attached. Thanks alot!
I think I'm on to the 123 ignition... kinda intimidated. The 123 has the ability to store two curves. Do you know if the second curve can be applied without having to install the toggle switch? I haven't dove into that yet.
 

·
But Mad North-Northwest
Joined
·
10,205 Posts
Do you have the manual? I'm trying to download the PDF but the link is busted.

Sounds like you have the USB programmable version? Yeah, there's one wire that, if grounded, selects curve #2. If you don't need to switch between curves you can just leave that wire disconnected and only program curve #1: it'll work fine.

Also note that I don't think the USB version comes with any advance curve programmed. So if you didn't program anything you may not be getting any advance, but I could be wrong.

Anyway it's pretty easy. Just add the advance/RPM points above and set the rev limit to 6500. If you've got the vacuum advance model and it's not hooked up just leave the vacuum advance curve zeroed out. Then send it to the distributor. Hopefully it came with the manual as like I said the link is dead.
 

·
But Mad North-Northwest
Joined
·
10,205 Posts
So I could only find the USB manual in German 😅 Ran the PDF through a translator and it came out reasonably comprehensible, let me know if you need it.
 
1 - 20 of 28 Posts
Top