Dhla 40 F Set Up And Options

[Sprint2000]

I have a pair of DHLA 40 F carbs (very good condition after a refurb by Eurocarbs) on my Alfa Romeo 2000 Sprint.

 

It's a 1961 102 Series engine, not to be confused with the later 105 series 2000 GTV type. ie: this engine has a Cast Iron block with Aluminium head. (50 years old)

 

'm looking make the most of the carbs and have a current set up that seems to be working well, but I'm looking for more from it (if I can get it).

 

Engine specs:

2021cc (bored from 1975cc original - fully rebuilt about 3000miles ago)

135bhp / 134lbft

Bore: 85.5/ Stroke: 88mm/ 4 cyl

Compression: 180psi

Domed chamber

Valves: Inlet 42/ Outlet 47

Warm cams

Separate-choke inlet manifold

Pertronix Ignitor ignition/ Flamethrower coil

Magnecor leads

NGK BR8 EIX plugs

 

Carbs:

Twin DHLA 40 F

Mains: 150

Airs: 200

Idles: 65

Em tube: 7772.11

Accel pump jets: 35

Choke: 32

K&N filters (83mm) with trumpets (43mm)

 

Like all road cars, I'm looking for best possible tractability and as much top end as I can get. This current set up seems to provide smooth progression but feels like it flats-out a little early at about 5000rpm.

What I want to get is as much punch as I can. Top speed isn't an issue, it currently sits happily at 90mph. Plenty fast enough for a 50yr old Alfa.

 

Is there anything you guys might spot here that I could try adjusting? These cars (although very pretty) are not very quick, so anything we can do to give them a hand makes a big difference. I plan to get it onto a rolling road some time soon, but thought I'd seek some advice here first.

 

One issue I do have is a sense that after / during long distance motorway trips, that the mixture goes off. I'm wondering if vibration is moving the mixture screws at all? - The carbs are mounted with aluminium carb mounts with heavy rubber O rings and deep soft rubber grommet washers. (Not the original stiff rubber carb mounts). As I don't have any gas-analyzer equipment (other than a colortune - which is only useful, if at all, at night) i end up having to guess the mixture adjustments until I am able to get it back to a workshop - I need to get the carbs set up as best possible and then perhaps use some 'tack?' to hold the mixture screws in place.

 

Any thoughts at all? Any advice much appreciated.

 

 

Here's some pics:

[DaveNotSoSideways]

Hi,

 

NGK BR8 EIX? Sounds like a modern EFI plug?

 

Fit some proper plugs, the real cheap ones that suit old engines? Fit whatever matches the original spec ie BPR7ES etc. Expensive plugs are often useless in old engines. 8 is VERY cold and those tiny iridium tips just hate sidedraughts, probably causing the engine to operate oddly in and out of traffic and from hi-to-low load changes.

 

The mixture goes off? The screws won't be moving, forget that idea. It'll be an issue related to incorrect fuelling, ignition advance, plug type.

 

Mixture screws control idle and just off idle mixture, the motorway/driving mixture is done via the fixed metering jets.

 

I can't believe the engine needs an 8 grade plug, cold plugs just give stogdy performance unless your racing/tuned up highly and running lots of compression; chamber heat.

[Nick Jones]

What a nice car

 

Tend to agree with Dave on the plug front. Never had any luck with plugs with exotic tip materials (platinum/iridium). Do rather like the triple electrode Bosch ones as used on 80s/90s VAG cars - I think the side electrode helps on the Triumph chamber shape. I suppose the fine electrode will tend to give a wider effective heat-range but would probably still be worth trying a set of ordinary plugs. I'm off NGK just now (PI kept killing them), but Denso and Bosch both do fine alternatives

 

Another thought on the "going off" after a long fast run. You have K & N Filters on there, breathing engine bay air. After a long hard run, especially when you slow down and the airflow through is lost, but the engine is still very hot, that engine bay air is going to be hot and that WILL affect the mixture the engine sees. This effect will be more marked if the jetting is a bit borderline anyway. I'm thinking that the hot air will be less dense, tending to lead to richer running.....

 

Cheers

 

Nick

[DaveNotSoSideways]

Originally had an airbox on the engine, suggest refitting it, it will CHANGE the jetting requirements though due to extra depression caused by the airbox and float chambers/airjets being at the same pressure inside a sealed environment.

[STIV62000]

Lovely car.

Smaller engined Alfa 2600.

I totally agree with the above, but feel your pump jets may be a little small.

How is it when your cruising and then accelerate away? Do you get a flat spot with the 35's?

We set up a similar Nord engine and needed 40's. My 1750cc with a few mods needs 40's too.

Spark plugs should be NGK BPR7ES. Or try the Golden lodge plugs Alfa used to recommend so religiously.

Good luck.

[Sprint2000]

Much appreciated, thank you

 

Over the last year or so I've been running B7ES, B7EVX and can't notice the difference - maybe the EVX is a little cleaner on acceleration. I'm trying the B8 EIX for longer runs and seeing what they do... so far much the same in town as the 7's, but I've only had them in for a day, so need more time on them to know for sure. I may well return to the 7 EVX as the norm and only use the 8's on long runs... something like that. (The original Lodge Plugs were Lodge 2 HLN/G - can't find these any more I don't think) - interestingly, the plug-coverter websites I've used end up giving an 8 value for the replacement.

 

I've not got a noticeable flat spot with the 35 pump jets, but happy to try 40's - so will get a set and see what happens. What I really need is a good rolling road with plenty of Dell Orto jets on the side and an experienced operator... but finding one is proving pretty tricky. (I live in West London). I think it's going to be the only way to assure myself of the optimum settings, rather than the 'seems happy, pulls well, runs ok across the range' settings I have got it to so far. I assume you guys think the other jets are sized ok?

 

Interesting comment about the advance... It's an original Magneti Marelli S73B (no vacuum) distributor (with pertronix Ignitor1 collar installed). Original springs. I'm very tempted to get the 123Tune and set the curves up on the rolling road. Do any of you have any experience of the 123Tune? The current springs work ok and it advances quickly up to a max of 42deg (original engine spec is a massive 47deg) but I'm sure could be better set up with a newer, more sophisticated distributor.

 

The air box thing is tricky... originally this engine had two intake options: Solex PH44 with a siamese inlet manifold and cast cold air box, or, there was a Weber DCOE 'upgrade' that had a single choke inlet and a cast cold air box. As time has gone by, the weber manifolds etc have all gone and so a Conrero copy single-choke manifold is the only way of getting single chokes (unless I weld up the original Solex siamese inlet). The new manifold mount pattern is different (closer together) and so the old air box wont fit it. So unless I get that cut up and re-machined I'm stuck with the K&N's. But I do agree that the lack of cold air is likely to affect things as you suggest. Need to think on whether to cut up the original airbox to re position the mounts (see pics for ref below) or weld the original manifold, or just leave it all as is... thoughts appreciated.

 

At the risk of showing my ignorance, are you sure the mixtures cant change through vibration? If it's not the screws, is there any other way this could happen within the carbs? I'm sure that after having gone a on a long run, that the performance changes... exhaust note goes flatter (less 'rasp') and it's still the case the next day (ie: when cold). Do you guys have any suggestions on who I might call to help me work on these carbs for tuning? If I could get you all in the same room, I'm pretty sure we'd sort it...

 

If it were you, what you check, and in what order?

[STIV62000]

I know most people will say the 200 Air correctors are about right, i thought so on the 1750 until i played around with the wideband. Truth was they were way to big for my engine on 150 mains, and i was leaning out above 5000rpm. Im down to a 160 air corrector with 150 mains and it holds a good afr of about 12.5:1 up to 6500, then begins to lean out to 7200 rpm at about 13.5:1. I dont go past 6500 so its ok...if i did id be onto a set of trijets, for the extra circuit to play with.

Id check yours with the WB and see what it needs.

With your engine you mite be ok.

Edited July 14, 2011 by STIV62000

[Sprint2000]

So, I've been on a rolling road this week and changed the jetting dramatically.

I'm hoping to get some opinion on an issue that I now have.

 

It turns out my original jetting was too rich and that my new set up is much more responsive, adds more power throughout the range, especially at the top-end and uses less fuel... all good. Except an obvious hesitation - even when warm - when I press the throttle firmly. It's much less obvious when I accelerate gently.

The hesitation clears quickly and from then on (with foot still pressed down) the engine pulls cleanly and well all the way up the revs. Until the next time I need some throttle. It can happen at any revs, but only the once - when I press down firmly for more throttle.

This is not a characteristic I had before.

 

This is what I have done:

 

Previous set-up:

DHLA 40 F

32 chokes, 200 Airs, 150 mains, 65 idles, 35 pump, Em.tube .11, when checking Floats it turned out they were poorly set at 12mm and 16mm (!), fuel pressure regulated through FilterKing at 3psi

 

I now have:

DHLA 40 F

32 chokes, 170 Airs, 130 mains, 65 idles, 40 pumps, Em.tube .11, Floats 8.5 @ 15mm, fuel pressure regulated through FilterKing at 4psi

 

I think this is pump jetting? But I have 40's on now and they are only marginally better than the 35's previously. Or could it be the smaller mains making this? I'm concerned to add larger mains as the new setting gives me a noticeably better range and crispness, with more power too. I tested this with 135 mains on the dyno and it wasn't as clean.

 

Advice for fine tuning this set up (on a real road) - so I can buy the right jets would be appreciated.

 

Many thanks

[DaveNotSoSideways]

At what RPM is the hestitation worse, is there is any variablity?? Does it immediately stumble or after a short period of clarity?

 

You can make the pump jet squirt a larger/smaller quanity over a greater/lesser period by making an adjustment to the pump rod under the carbs, carefully undo the locknut/nut using two small spanners adding no torque to the rod itself (or you'll break the small rod), moving the nuts up increases the quanity/potential period of squirt, down decreases the quanity. Move each side the same number of turns, 2-3 turns at a time and test results.

 

If could be a rich stumble or a lean one, any smoke evident in the mirror? Try booting it with the sun behind you to see the cloud of smoke if rich etc.

 

Could be the air correctors are a tad small, running 140main and 185 corrector would give the same mixture over a slightly adjusted range etc.

 

Are the 35 and 40 pumps both the same type? There are backwards firing jets (hole on the side of the shank) and downwards firing, hole in the base of the jet.

[Sprint2000]

At what RPM is the hestitation worse, is there is any variablity?? Does it immediately stumble or after a short period of clarity?

 

I get an initial moment of response, then just as quickly there's a sudden 'drop' in acceleration and then an equally sudden clear. Once passed the 'dirty' bit it seems to pull all the way up cleanly.

By the way, when the engine is at 80degC it is much happier than before this temperature.

It can happen whenever I boot it. No matter the revs. But it's probably less of a stumble at higher revs (passed 3000) than it feels at the lower end.

 

You can make the pump jet squirt a larger/smaller quanity over a greater/lesser period by making an adjustment to the pump rod under the carbs, carefully undo the locknut/nut using two small spanners adding no torque to the rod itself (or you'll break the small rod), moving the nuts up increases the quanity/potential period of squirt, down decreases the quanity. Move each side the same number of turns, 2-3 turns at a time and test results.

 

Thank you. Should I try this before or after playing with any jetting variants?

 

 

If could be a rich stumble or a lean one, any smoke evident in the mirror? Try booting it with the sun behind you to see the cloud of smoke if rich etc.

No smoke evident, I've tried that, but will do again, the AFR scores seemed good. Between 12 and 13.6 from 1800rpm through to 5500rpm.

At its leanest between 1200 and 2400, then getting steadily richer between 2400 and 4200rpm, then leaning off again from 4200 up to 5500 (giving the same AFR scores as at 2400rpm)

 

Could be the air correctors are a tad small, running 140main and 185 corrector would give the same mixture over a slightly adjusted range etc.

Great, ok. Will get some and see how that works. Perhaps as you say it just needs more fuel with the same mixture. However, I did try 180/135, 180/130 and 160/135, 160/130, but the 170/130 mix gave best AFR and power. What do you think I would see with your suggestion? I could do with some of your experience/ advice to help me understand the pros/cons here.

 

 

Are the 35 and 40 pumps both the same type? There are backwards firing jets (hole on the side of the shank) and downwards firing, hole in the base of the jet.

They are both downwards firing. What would I see if I changed them to the backwards firing?

 

Many thanks for your patience and help. I'm super-keen to get this just right.

Edited July 30, 2011 by Sprint2000

[James]

I don't know about your carb issues but I want to say that is a drop dead gorgeous car! I have always loved these Alfa and this one is beautiful!

[Sprint2000]

I don't know about your carb issues but I want to say that is a drop dead gorgeous car! I have always loved these Alfa and this one is beautiful!

 

Thank you James. Very nice to hear.

It's a great car, and they only made 704 of them. Too expensive back in 1958-62... list price was £3,500. An Aston was £4k, so you can see why not too many were built.

Weirdly it's now only 1 of 5 runners left in the world. There's a few 'dead' ones stacked up here and there, but this one's the only one in the UK.

[DaveNotSoSideways]

I can only point you in a direction, you need to experiment.

 

I suggested 140/185 as an example only.

 

You should have a play with the pump system first. Pump system isn't really working over a 1/3rd throttle, it works on the lighter throttle positions / intial opening of the throttle from any RPM, from closed position.

 

If the engine is better warm it's most likely a lean miss. Remember that on the rolling road the entire induction is heat-soaked and will need less fuel, so a 135main might be better, or more pump jet, or pump quanity.

 

It's not exact science, you need to make calculated adjustments and see what effects they make, and revert or progress in direction of adjustment as needed.

[Sprint2000]

Thanks again.

 

I was wrong about the pump jets...the 35's are backward facing, the 40's are downward. What is the difference in performance between rear/downward jets?

I do get some smoke at the mid/higher (3000rpm when the mixture is at it's richest AFR), but it's not obvious earlier or later in the range.

The stutter is not noticeable under free-revving - it's crisp and clear - no hesitation.

 

It ONLY happens on load and is repeatable at a particular throttle position (approx at 1/3 pedal). I can also create a much milder stutter at more open throttle if I suddenly floor-it. If I'm gentle, there's no stumble at any revs. This makes me think it's happening when the carbs come off pump jets and onto mains. However, could the idle jets be the culprit? I once tried running 60 idles on the previous set up and it coughed and spluttered over progression/heavy acceleration, then I put in 65's and all was good. I wonder if I need even larger idle jets now I have smaller mains, say a set of 70's?

 

Unless you disagree, it looks like I should try the following (one at a time of course, reverting or progressing as you said):

 

1. Bigger pump jets (45) - sidefacing

2. Bigger mains/ Airs (140/180)

3. Tweaking up (richen) the mixture screws a fraction of a turn

 

Any other things for me to consider?

Edited August 1, 2011 by Sprint2000

[DaveNotSoSideways]

It shouldnt need 70 idles. That's massive.

 

Pump jet only works as a fuelling device when you are massaging the throttle pedal, actively opening it and accelerating in the intial phase of a pickup of load/rpm/speed and mainly below 3500rpm but it can have an effect coming from closed to open throttle at higher rpm but only when you slap the pedal open. So if your issues only happen when you are opening the throttle and not creeping it open gently or at a level position then you are advised to play around with the pump jet.

 

If you can creep the engine through the RPM range in a gentle acceleration in any gear with no fluttering, stalling, spitting, or missing the actual jetting (idle, main, tube and air corrector) is probably sound.

 

The rearward firing pump jet gives a shot of fuel directly inline with the airflow, this means it can lead to less atomised fuel delivery as the stream is just ingested into the cylinder, worse hydrocarbon levels but a crisper and more reliable result, the downward one sprays fuel downwards into the base of the barrell when it's kind of sucked backwards against the walls of the barrel/inlet manifold/throttle plates and this often leads to the fuel getting to the cylinder less quickly but at the same time it gets there with less suspended droplets so it actually gives a cleaner unburnt hydrocarbon count at the exhaust. The downward fires were mainly used on emission spec carbs when the emission laws tightened, most racing/tuned engines used backfires.

 

I'd probably stick to backfiring jets.

 

To make matters more complex there were 3 types of pump diaphragm but Eurocarb etc only stock one type, the different types allowed more or less action/throttle opening to operate with the pump system. You might find it's not quite operating over the range needed due to the design of the diaphragm being universally incorrect. You just have to persist with pump rod and jet adjustments and experiment.

 

Worth trying some 45 jets and trying them in combo with the other jets, back to back, pick the best: then try the pump rod adjustment I suggested to increase the fuel quanity. Also if you adjust the pump-rod nut moving them upwards the pump jet will operate deeper into the throttle opening, at the expense of early opening operation at extreme adjustments. So could counter any defiency within the diaphragm.