[Gubi]

Well, that jetting seems right per the book. You're sure you have the correct idle jet holders without the air bleed holes, correct? They should look different than the ones on your regular DHLA 40 and will not have the second, lower row of air bleed holes. See photo of the correct idle jet holder for a 40F:

10738 Dellorto DHLA/DRLA Idle jet holder - Eurocarb

Without air calibration hole, only to be used with Dell’Orto DRLA and emission control variation DHLAs ie:- DHLA 40 F, DHLA 40 G, DHLA 40 H (non turbo), DHLA40L, DHLA 40 N, DHLA40R For all early DHLA40s, 45s and 48s use part number 7850 NOTE : These have been marked as 7850.N in error

www.dellorto.co.uk

When you say "the pointers bounced around" is that on the manometers? If so, that's because you need some sort of restrictor orifice on the hoses to smooth out the pulses. See the Carbtune instructions where they talk about "dampers": it's a section of narrow tube that you stick in the rubber hose to even out the vacuum. With something like that in place the manometer readings should be steady. It should go near the carb end of the hoses.

https://www.carbtune.com/inst.html

 

[Blackspider87]

Hello Gubi

thank you for those helpful informations ! To be honest... I need to check the Idle Jet holders. I am not sure.... if they are with or without the second row of bleed holes. What I did today..I worked with the Idle air bypass screws. Now all vacuum numbers are the same @ 2 hg. also the balance between front and rear is 100%. . But the rpms are still not steady /stable. The idle mixture screws are 3.5 turns out... Ignition is now 7 deg BTDC. @ 900-950 rpm.

So after all that work... I went back to the 40DHLA ( no letters ) .... and - the engine runs smooth.. Crazy - isn´t it ?
Only the third cylinder needed 0,75 more turns on the idle mixture screw than the other 3 cylinders. They are 3 turns out...

 

[Blackspider87]

here is the Alfetta GT.... ( my newest "Toy ")

 

[Gubi]

So after all that work... I went back to the 40DHLA ( no letters ) .... and - the engine runs smooth.. Crazy - isn´t it ?

Man, that's weird. Something is clearly wrong with the 40Fs but I'm not sure what.

Yeah, check the idle jet holders. Long shot but I'm out of other obvious ideas.

 

[Blackspider87]

will take a closer look tomorrow.. But I think that the "IJHs "are not the problem

 

[Rick4003]

Hi Blackspider,

Do you have any updates regarding the DHLA 40F carbs?
I am also running a pair of these on a 1967 sprint veloce and is facing some rough runnning/ bad idling problems as well. The carbs have been apart, ultrasonic cleaned in a mild detergent and reassembled with as much care to blow out all the canals as I could.
The engine is newly rebuild with new pistons & liners, ground crank, rebuild head with new valves and guides. Original cams. K&N filters
Valves lash have been adjusted to 0.48mm inlet and 0.52mm outlet.
Cams are also in the correct timing for TDC. Lines up perfect on the marks.

I have confirmed that TDC on the pully is correct, 123 programmable distributor is set with the green led to TDC and static timing + curve is set in the software. Position checked with timing light and ok.
I have a new fuel pump and a filter king regulator. I have not been able to test fuel pressure, but I don't really suspect this to be the rout cause of the rough running.

Floats are 7.5g set at 15mm closed/25mm open.

As I recall the jets are as below
Main 130
Emulsion tube .11
Idle 60

Venturi 30mm
Can't remember the auxiliary venturi but all are the same type and I don't believe these have been replaced.

Idle screws are currently at around 7-7.5 turns out which by the book is too much.

Cylinder 3 seems to be the problem and I suspect something is blocking the idle/progression canal on this cylinder. So despite the thorough cleaning (I thought) it might not have cleaned out everything.

I have tried to balance everything with a carbtune pro 3 and this helped for sure but it is still not possible to adjust cylinder number 3 satisfactory.

I will try and disassemble the carbs yet again and try to clean out the passages one more time and report back.

Looking forward to hear your results with your 40F.

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[Blackspider87]

Hello Ulrik

funny.. things first : Number 3 cylinder is also my problem here..

Now lets talk about your Problem... you have a 1600 cc engine ? I am not sure but your jetting is very stange. 130 mains .. and 60 idle jets ? My 1800 cc has 145 mains and 55 ! idle jets. your are writing, that you need to turn the Idle mixture screws 7 + turns out...way to much -also if you use 60 idle jets. 3-3,5 turns is normal.

Did you check the intake rubbers ? and.. the ignition curve ? I found out that the OEM Distributors i.e. Bosch or Marelli work much better - if they are not completly worn out.

As for the Ignition curve... the Alfas like 4-8 deg at idle... not more... because too much deg @ idle ,and you loose control with your mixture screws.

About your new KING Filter. I stepped into the following trap - the fuel pressure was way to high ! When I installed him I didn´t check the fuel pressure... Result : The high fuel pressure flooded the carbs.. and the idle speed was way too high.. nothing worked to bring the idle spped down. Until I lowered the fuel pressure down to 3 psi .

Valve clearance is o.k. float setting also..

Greetings from Germany Juergen

Note..... for a 67 Alfa I wouldn´t use "Letter " carbs.. DHLA 40 without Letters would be my first choice.

Note 2 while cleaning the carbs..did you remove the Idle air correction screws ??

 

[Gubi]

I can't see why the letter carbs wouldn't work in a 1600: Alfa used them. Closest jetting I can find is an Alfetta 1.6 with 40F: 132 main, 55 idle, .8 emulsion with 30 chokes:

If your idle screws are 7 turns out with the larger 60 jet then something is really wrong. Are you sure you have the correct idle jet holders for an F carb? See post #21 above.

As for the Ignition curve... the Alfas like 4-8 deg at idle... not more... because too much deg @ idle ,and you loose control with your mixture screws.

I dunno what to tell you, but with the vacuum advance my 2L GTV idles at 21 BTDC (6 static + 15 vacuum). The mixture screws still work okay.

 

[Blackspider87]

@ Gubi when you use a vaccum advanvce, then surely you can get 20deg BTDC. But with a NON Vacuum Distributor , the advance @ idle is limited - unless you change the curve in the distributor. And there is another thing... you get the 21 deg with full manifold vacuum (not ported - right ?) So when you hit your trottle the vacuum breaks down , and the distributor works like a "NON Vacuum ONE ".

Rick 4003 has a 123 Ignition. perhaps with vacuum advance..but the DHLA40F does not have vacuum source. so he needs to drill a hole into the manifold ,or into the carb to get manifold vacuum- if he can use it.

As far as I see the jetting charts for 1.6 Alfettas.. he has the wrong set up.. smaller mains.. bigger idles the emulsion tubes ... he has .11 instead of .08..

 

[Gubi]

That's all true. My point was just that – when I set the mixture with the idle screws – I'm doing it while I've got 21 degrees total advance and the mixture screws do not lose control.

As far as I see the jetting charts for 1.6 Alfettas.. he has the wrong set up.. smaller mains.. bigger idles the emulsion tubes ... he has .11 instead of .08..

That's true as well, but wrong main jets and emulsion tubes won't cause the idle screws to be so far out. Something else is going on.

Ulrik, you check for leaks at the carb mounts? Spray some carb cleaner around them, if there's a leak it'll get sucked in and you'll hear the engine run differently.

 

[Rick4003]

I can't see why the letter carbs wouldn't work in a 1600: Alfa used them. Closest jetting I can find is an Alfetta 1.6 with 40F: 132 main, 55 idle, .8 emulsion with 30 chokes:

View attachment 1793096

If your idle screws are 7 turns out with the larger 60 jet then something is really wrong. Are you sure you have the correct idle jet holders for an F carb? See post #21 above.



I dunno what to tell you, but with the vacuum advance my 2L GTV idles at 21 BTDC (6 static + 15 vacuum). The mixture screws still work okay.

For sure the DHLA 40F is not the original carbs for the car, but if I can get these to work well, then I will stick with these instead of having to find a no letter set.

I checked the setup again and the emulsion tubes I have installed are 7772.10 not .11 as above post.

The 60 idle jet is likely too big as suggested and my next step is to take the carbs apart again and see if I can clean out all passages as something must surely be blocking the idle passage in cylinder 3.

the 123 distributor does support vacuum advance and a port is made in the inlet manifold to support this. Currently these are blocked off to see if that was creating a vacuum leak. The distributor is not current set up to use the vacuum advance, so this did not make a difference in the idle running. Do you have any suggestions for the setup of the vacuum advance? at which pressures should the advance take place and how much?

Thanks in advance.

 

[Gubi]

I just posted my curves here. Note that these assume the 123 was installed at TDC and not at the static timing point.

123 ignition problems

Hi everyone! first of all! Sorry for the long post! I'm hoping someone in this group can help me! I'm really about to give up.. So I bought the 123 Bluetooth version. it came with a programmed curve that was supposed to be the correct one for my 1983 spider, i had the bosch 0237002018 whit...

www.alfabb.com

I would just leave vacuum advance disabled and the port plugged for now. It will run fine without it and it's one more complication when you're troubleshooting. Sort out your issues first and then you can try enabling it.

Before you take the carbs apart again, I'd go through everything on the car first. Did you check the idle jet holders and check for air leaks as I noted above? Also ensure that all four idle bypass screws are closed when you're doing your initial tune and balance.

 

[Rick4003]

Hello Ulrik

funny.. things first : Number 3 cylinder is also my problem here..

Now lets talk about your Problem... you have a 1600 cc engine ? I am not sure but your jetting is very stange. 130 mains .. and 60 idle jets ? My 1800 cc has 145 mains and 55 ! idle jets. your are writing, that you need to turn the Idle mixture screws 7 + turns out...way to much -also if you use 60 idle jets. 3-3,5 turns is normal.

Did you check the intake rubbers ? and.. the ignition curve ? I found out that the OEM Distributors i.e. Bosch or Marelli work much better - if they are not completly worn out.

As for the Ignition curve... the Alfas like 4-8 deg at idle... not more... because too much deg @ idle ,and you loose control with your mixture screws.

About your new KING Filter. I stepped into the following trap - the fuel pressure was way to high ! When I installed him I didn´t check the fuel pressure... Result : The high fuel pressure flooded the carbs.. and the idle speed was way too high.. nothing worked to bring the idle spped down. Until I lowered the fuel pressure down to 3 psi .

Valve clearance is o.k. float setting also..

Greetings from Germany Juergen

Note..... for a 67 Alfa I wouldn´t use "Letter " carbs.. DHLA 40 without Letters would be my first choice.

Note 2 while cleaning the carbs..did you remove the Idle air correction screws ??

Hi Juergen,
Yes it might be a little strange with the big idle jets, i could not get it to run with a smaller jet and in Des Hammils book he notes that the emission type carbs often needs a larger idle jet to run well. So didn't think much of it.
- I am 99% sure that the idle jet holders are the correct ones for the 40F carbs. they are unmarked, but have only one row of holes.

I have the all aluminium intake stubs instead of the intake rubbers. It likely needs new o-rings as well, so I will try and source some of these.

The ignition curve is based on a curve made by a fellow AlfaBB'er with a 1600cc engine and 123 distributor as well. static timing set to 8 degrees BTDC - full advance at 37 degrees.

- fuel pressure. I will have to find a manometer and check what the actual fuel pressure is after the regulator.

 

[Gubi]

Sounds like you have the right jet holders.

Personally I don't like the aluminum mounts but they should work fine if they're sealing. Check that with some carb cleaner spray or something similar: if your mounts are leaking you'll never get the carbs to work right.

 

[Blackspider87]

@ Rick /Ulrik
my 1800 Alfetta engine came with those DHLA40F from the factory. The idle jets are 55 .. so 60 ist way too big for a 1600 engine. I think you have a leaking manifold. As Gubi says ... use some carb/or brake cleaner and check the intake for leaks... BUT BE CAREFUL WHILE WORKING WITH CARB / BRAKE CLEANER SPRAY !!
As for the Solid Mounts...I wouldn´t use them . The O-Rings need to be pressed in a perfect way...more or less pressure on those rings..and you will have a vacuum leak.

 

[Blackspider87]

forgot to say.. my idle jet holders ( 40 DHLA F ) also don´t have numbers.. nothing.

 

[Blackspider87]

was in my garage today... when I dial in the idle mixture screws. Cyl . Number 3 always need 0,75 turns more than the other 3 cylinders.. The same happend with the OEM "F " Dellortos... how can it be ???
I checked for vacuum leaks.. Nothing. Evrything is fine. So I changed the Idle Jets ..went down from 50 to 48. The engine seems to like the smaller jets. But the Problem with cyl 3 continues. Before the "carb session " I adjusted the valves.. intake 044mm exhaust 0,49 mm all the shims I had to use are i the upper range... 2.600 and up. So the valve seats are good for the next 150.000 km ....
Timing ( ignition /cams ) is also within the OEM Specifications..

By the way... Rick 4003 reported also a problem with cyl 3 .

 

[Gubi]

If cylinder 3 needs more fuel with both carb sets then it's probably cylinder 3 and not the carbs. You can do a compression test (or preferably leak down test) and see if there's anything different about that cylinder that would explain it.

How did that cylinder look on the manometer set vs. the other three (before you did the final idle air bypass adjustment)?

 

[Blackspider87]

...... good advise. So I have to make a compression test tomorrow. Unfortunatly I don´t have the leak down test equipment.
But perhaps I can buy such a tester tomorrow.
Will keep you updated...

Greetings Juergen

 

[Rick4003]

Just for a note, I took off my carbs yesterday and noted that it looks like the lead plugs on the passage way for cylinder 3 looks like it has been tampered with in the past.

I have compression tested my engine and get 188-190psi on all cylinders, so nothing wrong there.



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