[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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[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.

 

[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.

 

[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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[Rick4003]

looks like I found the reason... the Number3 cylinder is the one where the linkage starts "to work ".. So the bearing and also the butterflyshaft is prone to fail exactly here. That´s what happend to 3 ..in words three ! of my carb sets.
The result of the defect is "wrong air / vacuum leak " ..just a little bit ..but enough to result in a shake and rattle idle..
Gladfully I had some 40 DHLA carbs (without numbers.. and with 3 progression holes ! ) At the end of the day (today )
I had one pair of DHLAs.. tomorrow I will go for a test drive

That is very interesting, in which way did you find that the butterflyshaft is failing? Failing in the bearings would that be seals starts leaking or the bearings that gets worn? I could imagine that the bearings doesn't get lubed all that well from so little movement.

So in three sets of carbs you had the same failure?

I have received all the necessary parts and are starting to assemble everything again. As you all suggested I will replace the all aluminium carb mounts with the original rubber type. I will need to fabricate a new carb support strut, but that will not be an issue.

One thing I did notice as I was comparing the new parts with the old is that the four new idle screws has a thicker taper than the old ones. It will be interesting to see how that effects the idle adjustment.

I will report back when the car is assembled again.

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