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Discussion Starter #1
Hi fellow alfisti im wondering if my carbs are set up properly for my 84 Alfetta gtv I purchased them fully rebuilt from Italy nearly ten years ago but never been fully happy with how the car runs they are dellorto dhla-40h here are the specs
Emulsion tubes 7772.10 / 8/ 11/ 8 yes they vary one per bank - I read that these carbs need different tubes per bank is this correct?
Main jets 148
Air jet 210
Idle jets 62
Accelerator pump jets 42


they have been tuned and balanced by an Alfa noticed the idle jet holder had the hole on top and from what I read for these carb being emission type should-not have the air calibration screw- can someone validate this? And if so is part number 10738 from dellorto ukhttps://www.dellorto.co.uk/shop/dellorto-car-carburettors-parts/parts/drla-parts/10738-dellorto-dhladrla-idle-jet-holder/ the correct part to buy?

the car runs the original air box but thinking of adding trumpets and has the 10548 cams thanks in advance for any tips / advice 👍
 

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Hi Alfapride,

You’ll need the single hole idle jet holders (10738 part #) and leaner idle jets, 62 is really rich, something in the 55-58 range. The 2 hole idle jet holders are for the early carbs “pre emission” (2 holes when looking side on)

The emulsion tubes should be matched, .8 richest, .11 leanest of what you have, .8 tubes would be best bet running 10548 cam. 148 main jet and 210 Air corrector sounds right and also common on Alfa

Be careful when ordering idle jets get genuine or known good quality ones as the idle jet sizes don’t correlate in mm, so a 58 idle jet is 0.54mm size hole. Sometimes generic idle jets aren’t the right size, or what you have has been drilled out.

Make sure everything else in top order, no vacuum leaks, float levels perfect etc before tuning to save yourself from going in circles.


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Thanks so much for the reply, this is my first time looking at carbs but I have some mechanical knowledge...ignition system rest of carbs etc all ok I suspect these carbs aren’t set up right as the original carbs fitted to the car which I had years ago ran better and I perhaps mistakenly bought these reconditioned ones thinking it was better to buy them rather than refurb the originals...I’m assuming these are set up different to the original spec...here is a side pic of the idle jet looks like 4 hole? I think there’s a hole where the screw driver goes in too so looks like the wrong one?
 

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They are the correct jet carriers. Your carbs air regulation for that circuit is fixed via an internal orifice in the carb body.
 

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I try to explain about the idle jet holders in this thread however I am not sure if its clear.

Agree with what Matt. The .8 emulsion tubes are the ones to get and yeah all should be the same. I.45 main jet and a 210 air. 55-58 idle. Check the chokes are the original 32mm because different chokes will obviously alter the set up.
 

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Hi, you may have the correct single hole idle jet holders there, as long as there’s no additional holes below the thread. For comparison can look up the 7850 pre emission holders on dellorto UK

The idle jets are not original though looking at number stamped on them

So some 4 x 58 idles, 2 x .8 emulsion tubes would be a good start

Here’s some factory DHLA40 H settings



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Discussion Starter #11
So I found this info on the forum also specifically for these carbs - what do you guys think of this any truth to it ? I wonder if this is the reason my carbs are set up they way they are??


Type 3 DHLA40F-G-H-N-R-S models. These are called emission completely different to the DCOE science, but noone really understands them and tries always to tune them like the early models. These differ because they have more progression holes and use the idle jet to feed most of the cruise phase and low rpm/low TP area of the engine AT ALL TIMES when the main jet isn't in operation completely automatically no jetting needed. The idle jet has a very large fixed 2.2mm air feed, you cannot tune this phase of the carburetor for length like the others, but here lays the secrets....

The idle jet doesn't feed from the float bowl, it feeds directly from the main jet stack, what happens after this is what gives these Dell'Ortos the sweetest road behaviour (what 25years of research came up with and not just for emissions) and dead easy tuning, you see when the main jet starts to emulsify fuel in the tube, the idle jet is feeding from it, so the gassy airy fuel shuts down the idle jet and sucks backwards yes BACKWARDS through the idle!! using every drip of fuel efficiently without ANY waste in circuit cross over where one is going after the other...this happens the moment the main jet fires, so there is NO need at all to tune the length of the progression and idle phase. This is pure magic they are automatically calibrated, you simply keep the idle jet above 59 up to 62and not make the mistake of fitting numbers suited to the early DHLA or DCOE - with this simple technique you can tune anything from a 1300 to a 2000cc without really doing anything.

The emulsion tubes in these carbs are always 8-10-11 and have to stay that way - which are really rich and have a hole straight down with loads of air holes, these atomise the fuel to an massive degree, also they have to be used cause the idle jet will not run correctly using the DHLA40-E type tubes (1-6-7-5) as the idle jet needs these airy tubes to function and cut out as designed...Usually people ram the DHLA40 idle holders with air holes in these carbs add the 1-6-5-7 style tubes and wonder why its a massive lean spot off idle, cause they missed the point completely!...These carbs use a .3 vent which has a very small signal tube to the main jet stack, this is because the holey tubes are basically ready to go from about 1250rpm (on my car using an 8tube 1 vent it was on the mains at 1250rpm!) so the holey tubes need holding back with a signal killing venturi...These carbs are wicked if you want bolt on power, they tune themselves!
 

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Discussion Starter #12
Continued - The emulsion tubes in these carbs are always 8-10-11 and have to stay that way - which are really rich and have a hole straight down with loads of air holes, these atomise the fuel to an massive degree, also they have to be used cause the idle jet will not run correctly using the DHLA40-E type tubes (1-6-7-5) as the idle jet needs these airy tubes to function and cut out as designed...Usually people ram the DHLA40 idle holders with air holes in these carbs add the 1-6-5-7 style tubes and wonder why its a massive lean spot off idle, cause they missed the point completely!...These carbs use a .3 vent which has a very small signal tube to the main jet stack, this is because the holey tubes are basically ready to go from about 1250rpm (on my car using an 8tube 1 vent it was on the mains at 1250rpm!) so the holey tubes need holding back with a signal killing venturi...These carbs are wicked if you want bolt on power, they tune themselves!
 

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Use a mirror and a light. The number is clearly stamped and is visible when you look into the carb throat.

Interesting that chart Matt has states except Australia. I have never seen 148 or 150 jets in standard carbs. Always 145 from the factory here.
 

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Some of what that post is about is correct but its also just a bit of a ramble. That last sentence about them tuning themselves is rather bazar.
With regard to you having different emulsion tubes in each carb you really have to wonder who and what the person that did that was thinking.
Remember fuel pressure, pressure regulator and float levels are also important.
 

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Discussion Starter #16
Have to look down the carb inlet, the size will be on the bottom of the choke, bit fiddly with the airbox but phone video/small mirror would help get the angle to see


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Cheers I had a look it’s a little tricky I think it’s 35 or 33 more likely 35...
 

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Some of what that post is about is correct but its also just a bit of a ramble. That last sentence about them tuning themselves is rather bazar.
With regard to you having different emulsion tubes in each carb you really have to wonder who and what the person that did that was thinking.
Remember fuel pressure, pressure regulator and float levels are also important.
Totally agree alfettaparts2

That site has good info on setting the floats/fuel level correctly


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Discussion Starter #19
Totally agree alfettaparts2

That site has good info on setting the floats/fuel level correctly


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Thanks guys really appreciate your help it’s hard to know what’s right or not sometimes when you’re learning...fuel pressure set correct to factory spec and I’ll have to assume for now float levels are aligned properly as I was told by my mechanic he did them at the time of tuning...
 
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