Idle problem 1981 GTV 2000

[fazersix]

Hi, after a few years I have finally got around to adjusting the balance and mixture on the stock DHLA40's.
It had been running rich, a few fouled plugs and a bit hard to start when warm until you rev it a bit!
After I have tinkered the the engine is initially idling at around 1300rpm, then after a minute or so it gradually slows and ultimately dies!
Setting the initial idle any lower and it dies much sooner! It does drive much nicer though and starts much easier!
I appreciate that things like compression, carb mounts (did see some cracking but have not tested this yet) and carb overhaul (probably well over due) come into play, but just wanted to know why it would be doing this! Any suggestions??
I foun dit really hard to hear engine rev changes doing the mix, but maybe I have to give it a few more shots/ cyl 4 was good but the others may be I didn't go rich enough!!
Before I made the changes, it idled around 900rpm, a bit rough but didn't die. It did run rich, plugs black and fouling every now and then
The settings before (previous owner):
Cyls      Screw turns        1      2      3     4
Mix                                5.25  5    3.5  5.5
Air bleed                        .25   .75    0     .75
Mix starting pint was 3 turns for all
After
Mix  (Approx)                 3.0     3.5   3.5   3.5
Air bleed                         0     .5      0     .5
Carb to carb also balanced

Am thinking of leaving the balance and go back to the original mix settings to see it will idle!
Any suggestions?

Cheers

[Colin Edwards]

The Dellorto is a great carby but has one shortcoming.  The air supply to the main and idle air corrector's is not filtered.  All air has to enter via that relatively coarse mesh screen on the side of the jet access "lid".   After some time the air corrector hole closes up due to contamination.  Any reduction in air flow through the corrector (or the mesh) will significantly enrichen the mixture.

Also need to ensure the return fuel flow back to the tank from the line between the pump and the carbies is effective.  Excessive fuel pressure will overcome the float and needle raising the fuel in the carby bowl causing mixture enrichment.  Are you running a pressure regulator?  Electric fuel pump?

Do both needles / seats reliably block fuel flow into the bowls when the fuel level reaches the set height?  Once idling, a main jet / emulsion tube / air corrector can be removed from the carby and fuel level observed by looking down the well.  The fuel level MUST remain rock solid at all times.

[fazersix]

Thanks Collin, some investigation to be done.
Apart from 10548 cam's the engine is completely stock!

[bonno]

Hi fasersix
In addition to Colins post, any cracks with carby mounts or dirty idle jets will cause the rough/poor  idle. I have link to a previous post on twin Dellorto on o/h, service and tune. The power point presentation included provides a detailed "How to" guide, together with various referenced links that maybe useful.
http://www.alfaclubvic.org.au/forum/index.php?topic=19598.0
Cheers
bonno

[fazersix]

Cheers Bonno I have seen that and a few others, they are great. That is how I learned to adjust the mixture and balance.
There is a solenoid bolted to the rear carb that is like a fast idle that has a screw adjuster to the throttle linkage. See photo
What is that and how should that be set since that could be part of my problem?

[GTVeloce]

Been a long time since I worked on a carbed engine... but IIRC that is a solenoid for your AC. When you switch the AC on the solenoid engages and raises the revs so it doesn't stall. Shouldn't have an effect unless it has been set incorrectly but I think it is fairly easy to remove to test.

Do you still have/use AC?

[fazersix]

After researching that is what I thought but the car doesn't have A/C And the solenoid is connected to the loom!
I will back that adjust re right back and so that it will never touch the throttle linkage . Maybe a previous owner replaced the carbs!
Cheers

[bonno]

If no A/C,  I would remove the solenoid and disconnect it at the loom. Additionally, to see whether the carb mounts are contributing to your poor idle I would place a smear of grease over suspected cracks and see if this makes a difference.   

[fazersix]

Hi Bonno I have just removed solenoid. The cabs are DHLA40G . I took the vent covers off took the jets out, nothing clogged mains are 145, pilots are 55 tubes are 7772.10.
The front vent gasket was dry the back was wet. Tinkered with the mixtures again, noticed the cyl4 POPPED occasionally.
It is reasonably happy idling at around 1400 revs.
If I try to set it lower, rev it and falls back to 1400 for a bit, then slowly dies are around 600 rpm.
I tried spraying Innox at the carbs mounts, no change in revs.
I guess that it is time for a carbs overhaul and New mou he since the look original.
Will do a compression test since last time I did it was a bit down but perfectly drivable!
Thoughts please?

[carlo rossi]

ok popping is too lean
for those cams the settings are wrong!
you need 210 air 7772.08 correctors  and 150 mains
idle jet at 55 ok lean a little \
your should be 4.5 turms out at the start
this all assumes the chokes are stock 32mm

[bonno]

Hi fasersix
FYI I have attached copy of baseline/standard specifications for 40 DHLA carbs fitted on Alfa Romeos. As Carlo indicated for your cams you might need to rejet to suit.
Was it always idling fairly high or did it get progressively worse over time ? ?

[carlo rossi]

if tghis doesnt work you have cracked rubber mounts

[fazersix]

Thanks for the info. It was idling around 1000 before and after I put the 10548 cams in.
Idling high after my attempt to tune the carbs. The chart is useful.
Living in Vic we don't get out much atm, so until I can get then new jets etc as recommended, i will retart the mixture  starting at 4.5 turns.
Will let you know how I go
Cheers

[fazersix]

Hi so just went to re-baseline at 4.5 turns and #4cyl mixture screw was a bit stiff turning it in. Oil can now only get to 2.5 turns out and the head of the screw it beginning to round - looks like someone else had this issue before me! Any suggestions on how to get this out? I did wind it back in a bit and the applied Innox, then out to 2.5. I am worried that if I apply any more force the head will round!

[bonno]

Clickable parts diagram for dellorto 40DHLA attached. The Idle mixture screw assembly consists of 4 items 60, 61, 62 & 57.  The condition of the o-ring may be causing a tight fit but is to be unscrewed in anticlockwise direction to remove.
https://www.dellorto.co.uk/clickable/dhla-parts-diagram/?TB_iframe=true&width=1024&height=800