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
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.
Thanks Collin, some investigation to be done.
Apart from 10548 cam's the engine is completely stock!
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
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?
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?
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
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.
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?
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
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 ? ?
if tghis doesnt work you have cracked rubber mounts
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
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!
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
Well I cannot unscrew it any more! It is 2.5 turns out the others are 4.5 and the car drives ok.
If I screw it in then I high that due to the rounding of the head I won't be able to back it out.
Beginning to think this is a drill and screw extractor to get it out and the re-tap the thread .
Has anyone done this?
Still high idle but am also thinking it is the mounts as Carlo said cos I recently changed the engine mounts and the carbs dropped without the stay on and i did notice some small cracking on the mounts (I think!)
The idle mixture orifice is machined to a fine tolerance and I would not attempt to drill and extract idle mixture screw. Recommend to liberally apply wd40 down the orifice and gradually remove idle mixture screw by unscrewing it in the anticlockwise direction. Ensure flat bladed screwdriver fits snuggly within the orifice.
i have this before, and the others ended up cutting the collar off
to relieve the screw slightly under the top of screw
when you get it out get a new one it could be cross threaded
Here is a photo of the idle mixture screw orifice (collar) and idle mixture screw (PS photo does not include spring, washer and o-ring).
Cheers Carlo and Bonno the task looks a whole lof better now. I removed the other barrels screw and can see that the thread starts approx 10mm down from the flags which is roughly in lime with the screw head.
So cutting the collar off level with the flange should a,low me to cut a deeper slot in the screw head well above the thread. This may take a few weeks cos I have to source the mix screw and tap (Dellorto Uk has a 7mm x .5mm tap).
Will get some gaskets and new jets and tubes as well. Will also do the carbs mounts, since they are most likely original.
Will post when I tackle the mix screw .
Quote from: carlo rossi on September 26, 2020, 03:15:57 PM
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
Hi Carlo I have checked all of the jets and tubes and found the air correctors to be 240.
I will go with your recommendations but what effect would 240 have?
240 is too lean pollution stuff
go the recommended settings dont play with other bypasses it will create hell
With a bit of patience and the use of a Dremel type tool I was able to remove the collar and re-slot the screw and was able to remove it with a screw driver. The thread turns out to good, so the binding must have come from the o-ring/spring!
Now to strip the carbs & clean and replace the carb mounts.
Hi Carlo
I just received the jets but I ordered mains 155 instead of 150. Do you think this will be too rich!
Also you said the idle jets are a little lean at 55 what would you recommend?
Cheers
no should be ok
we can adjust that out if needed
so the stack should be 210 ,77772.8 , 155
Yes that's the stack, thanks.
In the middle of a full carb clean out!
whilst they re off
whats the condition of the rubber mounts are they cracked
also if you have them out the next step is to change the auxillary venturi to 34mm from 32
but you will need 58 idles for that
Hey Carlo,
The mounts certainly had a fair bit of cracking on the outside, I didn't examine that much since I was changing them any way!
New ones are fitted and ready for the carbs.
I did not take the venturi's out so left the 32mm in - that will be a later project.
I have the carbs assembled and testing the pump volume.
Do you know the correct volume? The tag on the DLHA40H carbs say 1160360401100.
I have found some info on alfabb that say 20 sots per port 7-9 cm3.
So total of 40 shots should give 7-9cm3 total out put or 3.5 - 4.5cm3 per port.
Does that sound right?
I have the floats at 14.5mm and will check the fuel level is 27mm (so I have read).
Cheers
I have attached a link to a recently uploaded video that might help. The first part of the video is for bench testing fuel discharge rate (40 pumps should give 14-16cc) and the second part involving on car tuning. Please note this is specific to the 1300 Nord engine, but are the same from my experience on servicing the twin Dellortos on my Alfetta GTV 2.0L, particularly for setting of idle mixture screws and balancing. Apart from internal cleaning of carbs, the fitting of service kit will ensure you will get the best possible result.
https://www.youtube.com/watch?v=eKEqqimaF3M
Thanks Bonno I have watched a lot of Scuderia's video's.
His video is consistent with an alfabb post that has pollution model carbs 'H' which I have are in the 7-9ml per port = 14 - 18ml total for 40 pumps. My first result was around 12ml, after a slight adjustment I now have 16ml (8 per port), which looks good!
I have attached the document!
Carbs back on and first start up it ran and idled, ran like it had a fouled plug! Cleaned no 2 no change. Checked the fuel level it is at 27mm in the middle - I adjusted this on the bench using an old squeeze sauce bottle, gently squeezing to simulate 3lbs pressure which worked well!
Took some time to read and think things over then realised I had moved the carb sync screw during rebuild. Adjusted that and it is running pretty nicely, idling around 900rpm.
Now to tune the mixture and proper carb sync.
Update:
Had time to do the tuning, set mixture, using two gauge vacuum meters balance both ports in each carb and then then checked the carb to carb balance. Idling nicely around 900rpm and returning to idle after revving.
Test run, now revving sweetly and finally hits 6000 rpm.
Thanks to all who helped me on this post.
try and get hold off the 34mm chokes with 155 mains or 152mains with 32mm
Hi Carlo,
The 34mm chokes (because I am running 155 jets with 32mm chokes ATM) are around $100 from Eurocarb and could be a pain to fit if stuck. If I am lucky I can remove them whilst the carbs are on the car!
The 152 jets are around $50 and an easy change.
Will the 34 mm chokes give a noticeable performance increase over the 152 jets?
Cheers
really it only picks up the top end from 5000rpm to 5500rpm
particularly if 155 jets are too big
Hi since I don't rev past 5000 very often I have kept the 32mm chokes and changed the mains jets to 150 and the idles to 58 which appears to be a stock setup for a euro spec with 10548 cams. Re-tuned the carbs and it is running very nicely - smooth idle around 900 and pulls nicely through the rev range. Now on to the next project to drop the front by25-30 mm to make the car sit nice and flat - more reading of posts on the torsion vernier adjustment!
Good move to hang in there with the 32's. Although the 34mm diameter is 6.25% greater than the 32mm, the "theoretical" choke area of the 34mm is 13% greater! No point having "theoretically" 13% more flow potential if your not going to use it! Besides..............there is no substitute for gas velocity!
agreed the jetting should be good with 150 with euro and 32mm chokes
148 was stock
and it uses alot less fuel than the old cams
so much for pollution spec cams
but if you ever get the chance the 34mm chokes are wonderful
but you have change idles mains and such
hoiws the new emulsions tubes feel the 77772.8 should be perfect
Quote from: fazersix on October 30, 2020, 07:20:14 AMNow on to the next project to drop the front by 25-30 mm to make the car sit nice and flat - more reading of posts on the torsion vernier adjustment!
From a VERY distant memory, to drop an early, long T-bar Alfetta by a whole inch you can go one spline on the front only. No need to do the vernier maths to rtate the rear splines. Regardless, it's simple enough to give it a go and return it if you don't like the results (like a busted sump, or flattened 2-into-1 pipe, or like me, tore the headers off at the head.......).
If it were me, I'd raise the rear end.....