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Idle circuit problems on dellorto's - help ?


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#1 modular9

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Posted 25 February 2008 - 01:05 PM

To the guru's or at least someone who is willing to take apart there DHLA40 dellorto carb  and post some pics !

I got the dellortos on and sent the whole kit and caboodle off to a tuner ( I am lazy, as well as i had at the time , no idea about emulsion tubes and stuff like that).  He has put in the right type of jets and MAIN idle air corrector's but ...

the idle air correction circuit is a pressed in jet ( apparently ) and it is way too large ... So other than sticking a bit of fuse wire down the hole idea which I have done before on another carb but dont like doing, Is there anything else i can try ?

At the moment the idle is perfect and wide open throttle is perfect but the all important 80-90 % of driving rpm range of 2000 rpm up to 5000 rpm is a dog cos the idle correction circuit is letting in too much air. I have diagrams of DHLA's coming out of my proverbials and also how they work etc etc . I cant see the idle air correction circuit ( i can see the main circuit ) let alone any proof on if they are pressed in or not. 

Any help here would be great. I have contacted some alfa guys as well. They say to just unscrew the idle air correction jet and put a smaller one in . Not very helpful as the thing is pressed in !  ???

BTW anyone who is selling an EFI setup might get a call from me if i cant get these blasted things to work properly!

#2 JP240z

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Posted 25 February 2008 - 01:22 PM

Take out your jets. They are about 8cm long and accessed through the top of your carbs..
The jet is the small part that is pushed on the bottom end of the 8cm long piece. You should be able to pull this off with vicegrips. Ive changed my jets about a million times, if they are too big, you can solder them up and then just redrill the hole to the desired size..

#3 modular9

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Posted 25 February 2008 - 02:10 PM

afraid you were going to say that ! I'm going off to the place that has the car in the next 30 mins or so , so i'll be able to get a better idea . gonna tell him your advice.

Strange way of doing it Mr Dellorto !  ;D

#4 mick74

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Posted 25 February 2008 - 04:36 PM

What model dellortos do you have? ie DHLA 40 ?. Some models came with a fixed air bleed ( for your idle circuit) ie 2mm Diameter and this is too big, therefore too lean. Nothing but head aches when your just off idle until 4000rpm.
If this is the case you will need to make a sleeve with a smaller hole on the inside (this will make it richer).
Also check your emulsion tube for your main circuit, should be 7772.7 or .8.
You will also need to turn down (in) your idle mixture screw 1.5 turns out from fully in.
Also your jets will need to be adjusted.
I will get some photos from my set up and post them later tonight with jet sizes.

I hope this helps?

#5 modular9

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Posted 25 February 2008 - 06:42 PM

thanks mick 74 ... you got it one. I have dhla 40H 's with fixed air bleed ( the guys at the shop are calling it an idle air corrector which is where i got confused cos i know they can be taken out etc ) . I have attached a diagram from eurocarb of the area i am talking about. I really have trouble describing what i mean but i reckon mick74 has it.

The air bleed hole must be at least 4 mm i could put a blue pen nib ( metal part ) all the way down. The guys at the shop have never seen holes that large and they have never needed to work on that section of a dellorto before.

The consensus was that either a lead plug would be rammed down the tube and then drilled out or ARALDITE  over the hole and then drilled out. Seems odd but must be the way.

Mick 74 : thanks for the help and if you can , can you take a pic of the airbleed section with the size that you worked with.

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#6 mick74

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Posted 25 February 2008 - 08:13 PM

I hope this helps.
Slightly worked L26
Idle jet size = 55 (0.55 mm) , Air bleed resize = 0.9mm
Main jet size = 125 (1.25 mm ), Air corrector 240 , Emulsion tube 7772.6

Photos are of the Air bleed with and without insert , the insert has a collar on the top for easy removal and also that you cannot over insert, bore is 2.2mm for the air bleed (main body of carb) . This was done like this so that it can be resoldered and redrilled if necessary.

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#7 modular9

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Posted 25 February 2008 - 08:24 PM

Absolute legend. :)

If you are ever up in brisbane, tell me, and beer will flow.

This is exactly what I needed. I also reckon my carbs are the same regarding the original hole. Your engine tune is better than mine as i reckon i got a stocko l24 in a 260 but the main problem was the air bleed. I am going smaller in the idles and main jets I think. I dont have anything special in the engine.

Thanks again. This has made my day! and probably the blokes at the tuning shop as well.


#8 Toecutter

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Posted 27 March 2008 - 10:22 PM

I hope this helps.
Slightly worked L26
Idle jet size = 55 (0.55 mm) , Air bleed resize = 0.9mm
Main jet size = 125 (1.25 mm ), Air corrector 240 , Emulsion tube 7772.6


Hi Mick74,

Would you say the Air Bleed Resize would still be 0.9mm for DHLA40 L's? I believe you have DHLA40 H carbs as does Mike?


Thanks,
Sulio

#9 mick74

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Posted 28 March 2008 - 11:12 AM

Sulio

The idle circuit should be the same config. I’m not sure what model I have, will check when I go home, from the literature that I have read there are several modelled dellortos that have the same idle circuit design. (Remember that they are designed for a 4 cylinder 2 litre (500cc per cylinder not 430cc).

An air bleed of 0.9mm is a good start, then you adjust the idle jet size to get 1. Good idle and 2. Good progression phase (When the butterflies are cracked open and continue to be opened until 2/3 or ¾ opened, that is when the main jet becomes operational).

You need to open the idle jet enough so that your air/fuel mixture in your progression phase is right, and then you can adjust your idle via your idle mixture screw (this would be approx 1 turn to 1.5 turns out).

This is the principal the I have followed and works well, I have an o2 sensor hooked up to my extractors with a readout inside the car that makes this possible. The cost saved by doing this myself enables me to buy other goodies.

Regards
Mick


#10 Toecutter

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Posted 28 March 2008 - 10:24 PM

Thanks Mick, PM sent.

Sulio

#11 Glen

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Posted 11 December 2008 - 06:10 PM

Hi, Question for mick74, i just been doing some reading around and we (myself and friend) are in need of the idle restrictors for our dellortos. My set is DHLA40 with no following letter while my friend has DHLA40F's all matching. Is it possible that you can sell these mick?

#12 Glen

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Posted 12 December 2008 - 04:55 PM

i might pm him.

#13 Toecutter

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Posted 12 December 2008 - 11:13 PM

yer he's on night shift atm so not sure how often he's logging in. But I have a spare set of air restricters. I lost one though so maybe Mick can make one up or maybe when you see em you can make one up. Call me and I'll send em to you Monday so you get em in the mail Tuesday.

SUlio
0413 188 024

#14 Glen

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Posted 13 December 2008 - 07:12 AM

cheers mate.

#15 modular9

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Posted 13 December 2008 - 05:53 PM

and they work really really well. ( cant have mine  :P )



#16 Glen

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Posted 15 December 2008 - 10:49 AM

and they work really really well. ( cant have mine  :P )



just spoke to michael and im lucky as i dont need them :)

Sulio my friend still needs them so i will send you a PM with my address.

#17 Toecutter

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Posted 15 December 2008 - 03:50 PM

yep no probs.




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