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Sprint2000's Achievements
Learners (2/10)
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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?
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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.
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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. Thank you. Should I try this before or after playing with any jetting variants? 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) 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. 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.
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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
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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?
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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: