DellOrto DHLA 40 M ?!

[italcarnut]

Hi folks,

The guy that owned my Alfetta GTV before me installed a pair of DellOrtos and I am trying to verify that the venturies and jets are correct for this particular car. The Autobooks Alfetta manual says that the proper carb for the 2.0 is the 40 DHLA G, Main jet 1.45, correction jet 2.40, idling jet 0.55, idling air jet 2.20 Venturi ?
My car has to start with 40 DHLA M's. What does that mean? Is this the correct carb? Can you tell me which venturis and jets are correct for the M?


Regards,

Ruben Velez

[papajam]

I'm by no means a Dellorto expert but if they're anything like the Weber DCOE series, then it's not what jets are right for the carb but what jets are right for the engine. Without knowing what, if any, engine mods have been done, it's near impossible to say what jetting would work well. However, even with only slight engine mods, I'd say that the 145 main is too large as is the air corrector. Alfa fitted carbs with 32mm venturis to the 2l engines although 34mm work very well.

[Tassie Tuner]

The jets you have in your car sound like the emission control jetting that Alfa installed in the Dellortos on Australian market Alfettas between 1976 and 1986. It caused the loss of 6.5 kW (10 bhp), down from 96.5 kW to 90 on the 2.0 litre models. It was never really successful; causing flat spots and excessive lean running. It’s best to use the European jetting, which works well. In Australia, the air correctors were changed from 2.10 to 2.40, and emulsion tubes from 7772-08 to 7772-10 tubes, which had much larger holes in the sides of the tubes. The 1.45 main jets you have are correct and were as specified by Alfa, (they are not too large, as suggested by Papajam) but you should change the air correctors to 2.10, and install 7772-08 emulsion tubes if you don’t have them, and it will run well. Your idle circuit jets and air correctors are OK. You should have 32 mm chokes (venturis) in the carbs, which was the size Alfa used for their 1.6, 1.8 and 2.0 litre motors, according to the Haynes workshop manual – that was the size in the Dellortos in my Alfetta 2000 when the motor was standard. It was a compromise setting that was aimed at reasonable power with good drivability.

The Autobooks Alfetta manual you have may be an Australian edition, because it’s certainly got the Australian jetting in it. The Haynes manual I have, which has the UK market European jettings, agrees with the jetting I gave you, and I’m sure that when I had my Alfetta, the handbook also gave the European settings, because the jets were changed in Australia after the cars had landed from Europe, according to a magazine interview I once saw with an Alfa Australia mechanic. In my car, when I got it, in 1985 as the second owner, the air corrector jets and main emulsion tubes it had definitely didn’t agree with the Haynes manual, or the handbook that came with the car, so I changed it back to the European settings specified in those books, and the flat spots disappeared, and the car performed better.

If you run hotter cams then peak power will be higher in the rev range, and you’ll probably need at least 36 mm venturis (for around 6000 rpm peak power), which can be installed in 40 mm carbies, but are best in 45 DHLA Dellortos, and different jetting.

[italcarnut]

Thanks for the replies. This data is what I am reading in this book. I have not yet looked in my carb to see what I have, But the M on my carb has me confused. My car has 10.1:1 pistons, euro camshafts, Marelli Plex ignition, Euro exhaust ( no catalitic converter). When cold it runs like crap. Normal driving in summer is fine, but winter, Fugetaboutit! I just want a car I can enjoy and not one thats a pain to drive.

Regards,

Ruben

[Tassie Tuner]

Although you have a slightly higher compression ratio, (normally 9:1 for a 2 litre) that should increase power all through the range, not just at peak revs. So the chances are that the jettings you have, while a bit too lean for a standard car, should be OK - slight flat spots were all I ever noticed with mine when it was the standard jetting fitted to emission controlled cars. Change the air correctors and emulsion tubes for the Euro jetting, and it should be slightly better. However, if you're experiencing problems in cold weather, the first thing I would check is that it has a thermostat, and that it's the correct version for the car, and operating correctly. If someone has taken it out, or it's stuck open, it will take ages to warm up. In most Alfa twin cams, due to the all-alloy engine, they heat up super fast. However, when cold, judicious use of the cold start enrichment arrangement, and the hand throttle, is sometimes needed for the first few minutes. Chances are if you live in Pittsburgh, you experience much colder temperatures than where I am - it is an extremely cold night when the temperature drops below freezing point here, and only ever happens maybe two nights in the year usually. If you don't have the cold start mechanism hooked up, then you perhaps should do. Most of the time, it isn't needed - several pumps of the accelerator is all that is needed to start, and then it will run OK, provided some throttle is used to keep it running.

Because your Dellortos are probably aftermarket fitments, that's why they are a slightly different ones (DHLA M) to those fitted as standard equipment. However, there should be little if any difference in the jetting required. If you haven't checked the jets, it is just a 5 minute job - unscrew two screws and lift the black or white plastic covers fitted to the top of the carbies, then unscrew the brass jets underneath. On each carby, there should be 4 large jets - the 2 smaller ones are the idle air jets and idle jets, and the 2 large ones are the main jets, air correctors and emulsion tubes. They have numbers stamped into the jets, and you can check which ones are fitted. Probably for the idle air jets, they'll have something like ".1", which corresponds to a 7850.1 air jet. I think that's what they should be - you can check http://members.aol.com/dvandrews/dellorto.htm for details on which idle air jets are leaner and richer. They don't seem to correspond to the 2.20 value that the manuals show, but go by a special Dellorto part number, and according to my pencil jottings, I had 7850.1 idle airs fitted for both my standard carbs, and the DHLA 45 carbs I had when it was modified. The best way to get the jetting absolutely right is to get it set in a rolling road session on a dyno, by someone who understands Weber and Dellorto sidedraft carby jetting.

However, if it has trouble warming up, check the thermostat. On even the coldest day or night, it should be fully warm after maybe 10 minutes absolute maximum time - on warm days, that would be reduced to maybe 2 or 3 minutes. While we rarely get snow here, because it's on the coast, I have driven it, when it had several inches of snow on it, when we had our once in twenty years snowfall (about twenty years ago). I came out of the night class I was attending at the time, to discover a lot of white stuff around, and it was very cold, but from memory the Alfetta started up OK, warmed up quickly, and drove home with no spluttering or coughing. The heater was certainly fully warm when I got home, after maybe 15 minutes driving.

[okiealfaaddict]

Here is some very good Dellorto info:

http://cgi3.ebay.com/ws/eBayISAPI.dl...serid=alfa1750

[italcarnut]

Thanks Guys, you're the best!

Regards,

Ruben

[gunjamadness]

Does the engine warm up? you said it runs ok in summer but crap in winter maybe the thermostat is stuck open.

[jarripote]

Hi everybody, Lotus Sprit Turbo used Dell Orto 45 DHLA M twin carb , can be the "M" for Turbo application?