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PV, 120 (Amazon), 1800 General Forum for the Volvo PV, 120 and 1800 cars |
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carb tuningViews : 2269 Replies : 26Users Viewing This Thread : |
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Dec 5th, 2017, 14:54 | #1 |
arcturus
Last Online: Today 07:16
Join Date: Mar 2006
Location: Sagres Portugal
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carb tuning
B20b with twin HS6 4branch and D cam.KN needles i think. will check when i find paper. Can't get the engine to run below 15 flats an needle adjustment and settled on 20 flats. Is this right or could I have a problem? Normal starting point is about 12 flats
OK, its a senior thing. Can't remember needle. will need to search for spec's later
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life's too short to drink bad wine Last edited by arcturus; Dec 5th, 2017 at 15:53. |
Dec 5th, 2017, 18:34 | #2 |
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arcturus, what condition are the SU's in? If a little aged it's worth fitting new springs under idle/off idle screws + check for air leaks [especially on spindles] as these can throw 'off' idle/off idle settings when adjusting base air balance across the carbs. it's also worth checking jet and needle position, and equal spring ratings...and correct oil level [read equal] in dashpots.
Plus, it's near Christmas...so you may ask Santa for a copy of the SU Tuning Bible https://www.amazon.co.uk/Build-Power.../dp/1901295141 |
Dec 5th, 2017, 20:07 | #3 |
arcturus
Last Online: Today 07:16
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Carbs have recently been completely overhauled, new spindled etc. Funny thing is that the car has been running really well, lots of oomph. I took the car for it's annual inspection today and turned the jets down one flat, just to lower emissions slightly,. when I returned home I thought that I would just check things and discovered this issue. Engine runs great at 20 flats.Am I worrying unnecessarily?
BTW car passed with flying colors, just advisory for high emissions.
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life's too short to drink bad wine Last edited by arcturus; Dec 5th, 2017 at 20:14. |
Dec 5th, 2017, 21:43 | #4 |
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okay, if freshly rebuilt all should be good. I wouldn't worry too much if running a little rich providing the right needles are fitted. though the HS6's should still run at idle 600-800rpm with butterflies just slightly open as there's no load on engine [this one of the great things about SU's]. The only draw back with running rich is the risk of washdown of bores into the oil... :. have you a Gunson Fuel Colour Tune to go with your Gunson/other make air balancer? I find setting up carbs with air balancer first, then proper idle followed by off idle at 1500rpm, by which time the engine's nice and warm. Re-adjust ignition timing if necessary...and then use the Colour Tune as this gives a great visual indicator as to what's actually firing within each cylinder.
One thing that's very common with 4pots running twin SU's is that the rear two cylinders are often richer than the front two, especially when the engine's up to full operating temperature. Here, I sometimes slightly lean back the rear SU to get matched combustion colour. This then means all four cylinders are perfectly air/fuel balanced giving known equal combustion. The key here is that most manuals[Haynes and factory] only give basic set up process and miss the most important part, "is the engine running equally in all four cylinders". You may like to tinker more with the set up to ease off the rich[unspent hydrocarbons] fuel. Lastly, are you running PCV into the SU's? If so this type of archaic system can play havoc with settings. Here, I always running open vented/to atmos' with SU's as it makes no sense re-circulating unspent/heavily oiled HC's back into the SU when what we really need is pure clean air/fuel ratio. And of course, if an engine is combusting the air/fuel intake mix correctly it will exhaust fewer HC's than if crankcase vent/PCV is connected. Sadly, PCV re-circ' is simply a bodge to theoretically overcome exhaust emission controls. Good luck with the setting up. PS are the floats set up correctly, and/or, could one of the floats be leaking :. over opening 1no jet leading to slight overfuelling? |
Dec 5th, 2017, 22:02 | #5 |
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Arcturus;
D Cam is normally for the FI configuration, so running it with Carbs may require Idle mixture to be on the rich side to get it to run well the rest of operating range... (and this would be consistent with the high emissions finding...at idle?...or were emissions tested on a rolling road throughout entire range?) Idle at 20 flats might also be explained by the Metering Needle being "low" in Dashpot...you might verify that shoulder of MN is be flush with bottom surface of Dashpot. Finally, assure Level in Fuelbowls is not low...in the end, proof of the pudding is in the eating, but if the exhaust smells "Rich" you can try bringing up the Jets one Flat at a time, drive it for a few days, and note the results, and adjust to further optimize... Good Hunting! Last edited by Ron Kwas; Dec 5th, 2017 at 22:05. |
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Dec 6th, 2017, 10:11 | #6 |
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Just use one of these air speed gauges:
https://www.amazon.co.uk/Anemometer-...ir+speed+gauge You can do everything with them:
Of course, the thing we're talking about in this thread is mixture. If too weak, it's not running efficiently, so not running as fast as it should so intake air speed is reduced. If too strong, the same. That's why the air speed is fastest when the mixture is right. You can measure correct mixture throughout the rev range using the same anemometer: fastest air speed = correct mixture. If you find you have to re-adjust the mixture screw a lot throughout the rev range, then you know you either have worn out needles or the wrong needles. The only thing you can't do with the anemometer is check the fuel bowl levels! Agree entirely with the comments above with crank case breathing of which I am not a fan of oil fumes going back into the manifold. Good air and fuel is what you need! Personally, I am not a fan of either Gunson kit mentioned above. Okay, they both achieve near enough. The Colortune is alright, but a lot of fiddling about to match up the same colour in front and back. The Carbalancer is a complete no-no for me: as you stick the contraption over the chuff, it restricts air flow, so gives an inaccurate reading. Oh, and the little ball thing in the sliders sticks! I do not get adjusting mixture on number of flats or height of the piston from the jet. It's good enough to get going, but definitely need incremental adjustment with the engine running.
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2006 XC70 D5 Manual 1968 Amazon Estate, B18A + Overdrive 2019 V60 D3 Momentum Pro Manual 1970 Amazon 2-Door 1970 142DL Last edited by swedishandgerman; Dec 6th, 2017 at 10:15. |
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Dec 6th, 2017, 12:03 | #7 |
arcturus
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Thanks, it's actually what I use now! Didn't know that it could be used for mixture. I'm probably worrying about nothing. It's the first time I have counted the flats so it was probably OK before I re adjusted it. The moral is .If it aint broke don't fix it
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