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Discussion Starter #1 (Edited)
Could do with the help of some experienced Alfisti here.

I have Emissions Delorto's DHLA 40's on my 2L 86 Spider S3.

These are G variant carbs.

Current Jetting is as follows:

Idle jet: 50 (was 48)
Emulsion Tube: 7482.3
Main jet: 148

I think the other jets are stock. Background - when i was using 48 idle jets the engine would nose dive on anything from closed to half open throttle on the lower rev range. This problem has been sorted by going to a 50 idle jet.

Now here's the bigger problem:
If I accelerate on half open throttle or less it struggles, lacks power and crackles a lot between 2500 to 3000 after it kind of still struggles all the way up to 4500rpm.

If I open the throttle fully it doen't seem to struggle as much but I still feel a definite lack of power.

If I am cruising in 5th geart at 2500 rpm it seems like it just wants to die and sometimes i have to press the throttle harder for it to stay running. It's almost impossible for me to accelerate in 5th gear below 3000rpm and overtaking is impossible. certainly don't think this is right for a car that is quoted at 130bhp. I am not sold on these emissions carbs at all. And I do have a spare pair of solex's sitting around. Tempted to use them.

If anyone can offer some advice that would be greatly appreciated.

Rob
 

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50 idle size seems too lean - remember, they feed the progression holes, too, plus emission series have fixed 220 air holes; that might cause the missing at moderate RPM you mentioned. 55 to 59 idle looks OK for me. I'm running .57 IJs on H-series and it's pretty responsive already at 2K.

BTW, 7482.3 are starter (cold start) emulsion tubes, not pump jets. Pump jets are marked either 7851 or 8083 (the latter spray downwards). I'd expect something around .40 size...
 

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I have stock-jetted DHLA40G's on my Alfetta which had similar issues to yours not so long ago. I pulled them off & rekitted them, found a HEAP of crud in the jet chamber underneath the body, despite the float bowls and jets themselves appearing clean. It might pay to pop the accelerator pump off the bottom & have a look inside the chamber to make sure all is well there before you start throwing jets at it (best to pull the carbs off & do it on the bench)
 

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Richard Jemison
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Suggestion

Trade the pair of Delorto & Solex for a pair of Webers.

Far better tuning parts available and knowledge of proper set-up.
 

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Standard idle jet was 0.58 for DHLA40G. Accelerator jet should be 0.40. No need to change the idle air if it belongs to the emission type carb. Do you have the emission type main emulsion tube? Seems someone has just dropped available jets in your carbs?
Easy to find jets even for Dellorto on ebay.
 

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Richard Jemison
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Originally Posted by Alfar7
Trade the pair of Delorto & Solex for a pair of Webers.

Far better tuning parts available and knowledge of proper set-up.
Oh, c'mon...
Not to begin the mention higher air flow rates as well...

Solex and Delortos were the Accountants choice for these engines, not the engineers!
 

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Oh please, don't start another jihad here...
Sad truth, but most of us are really accountants. The true Engineering starts with this :cool:
 

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A bit hard to read some of them, but this is a chart of what different cars had and their factory jetting. Should give an idea on where you're starting at. http://www.alfabb.com/bb/forums/carburetors-fuel-injection-air-intake/159561-1972-2000gtv-dhla40h-jetting-questions.html

While I respect RJ's view on Webers and I agree that in a track car they tend to perform better, my personal preference for a street car is Dell'ortos as I find once they are PROPERLY set up, they seem to be more traffic-friendly and hold their tune much better. This is my experience anyway - horses for courses IMO.

But I would be DEFINITELY be pulling the pump chamber off & checking that for rubbish first. Even though it's a PITA job with the carbs in the car, it's no point changing jets about if this area isn't clean.
 

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...my personal preference for a street car is Dell'ortos as I find once they are PROPERLY set up, they seem to be more traffic-friendly and hold their tune much better.
I was fortunate to have been lent a 1967 GTV fitted with Dellortos to drive a few hundred miles to and from the 2004 USA National Convention. The ease of starting, idle quality and tractability on the road was an instantaneously recognizable difference from Webers. I was dully impressed!
Could the Webers offer better high end performance? Cut a few tenths off your lap time? Perhaps. But since I won the class by 10 seconds, it didn't matter.
 

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Discussion Starter #11
Thanks for all your advice.

Carbs have been taken off, cleaned and new kit / gaskets used. So I think this is defo a jetting problem. Someone recently told me that the idle jet was .57 which is waaaaay bigger than the.50 I am using. Could someone please confirm for emissions carbs what came of the factories for 2000cc engines? This would probably be a good place to start.
 

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Discussion Starter #12
OK, just bought .58 jets online. I will install them when they come and let you guys know the difference - apart from higher fuel consumption :D
 

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Discussion Starter #13
50 idle size seems too lean - remember, they feed the progression holes, too, plus emission series have fixed 220 air holes; that might cause the missing at moderate RPM you mentioned. 55 to 59 idle looks OK for me. I'm running .57 IJs on H-series and it's pretty responsive already at 2K.

BTW, 7482.3 are starter (cold start) emulsion tubes, not pump jets. Pump jets are marked either 7851 or 8083 (the latter spray downwards). I'd expect something around .40 size...
What main jet are you running, out of interest?
 

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Photo of typical "emission type" main emulsion tube 7772.10 and idle jet holder.
NB! There is only one type of idle jet holder for emission type Dellorto and it has no number stamped on it. (You can not use the "Universal Performance Type" idle jet holders, marked with numbers, on an emission type carb.)

E-tube 7772.10
Air corrector 220
Main jet 145
Acc. jet 40
idle jet... try 57 as a good start

And maybe you should see if the venturi really is 32mm?
 

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And the good auxiliary venturis are 7848.3 or 7848.1 for performance. (7848.2 and .4 works of course but is some kind of........ emission crap........ bad flow)
 

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Discussion Starter #16
And the good auxiliary venturis are 7848.3 or 7848.1 for performance. (7848.2 and .4 works of course but is some kind of........ emission crap........ bad flow)
Given that these are emissions carbs, if I get the jetting right do you think I could see a similar performance to normal carbs?

Also my emulsion tube is 7482.3 do you think these are optimal or not?
 

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That is the cold start emulsion tube. Has no function for driveability.
rsordillo, are you searching them in the wrong place or did someone screw starters instead of emulsion tubes? Theoretically, the threads fit...



Here are the starters (shot upside down, ONE per carb).

 

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Discussion Starter #20
Hi guys, thought I owe you an update..

I installed .58 jets, there were 60´s installed before the other day. Instead of getting my mechanic to tune it I did it myself. And do you know what. It runs much much much better. I used the vacuum device thingy to balance the carbs as they were way out of balance. It just goes to show that it's not always about doing it by ear. I then followed a procedure of backing the idle mixture screws out about 2.5 turns and then progressively until rpm was maximised. Once this was all said and done i dropped the throttle screw out until it settled at idling around 900 rpm car runs pretty well. I´m very happy of course maybe there's still room for small gains but i am definitely in the ball park for performance now.
 
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