Stu
Posted a lot
Posts: 2,913
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Apr 27, 2006 13:53:19 GMT
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Hello All, Yet another carb novice question from me. Now I've started using my Mk1 Golf a bit I notice that once warmed after a few miles it idles rather high, like around 2k rpm, possibly a bit higher. So, I want to lower the idle. Now in the past I've adjusted the idle ok with the screw indicated in the pic, under the throttle cable just about visible. However, once the car is warm even if I wind that screw all the way and the linkage/balance bar thingy hits it's stop the idle is still very high. Is there something else I can adjust to sort this out? I'm reluctant to start messing too much as the car runs well and starts fine hot or cold without even having a manual choke connected (must get round to that). Any ideas? A 2k rpm idle is rather loud with these carbs and probably not helping my fuel consumption but I wonder if it's been set up this way to get it to start nicely? Cheers Stu
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Last Edit: Apr 27, 2006 13:54:15 GMT by Stu
'89 BMW E30 325i Sport, '04 MINI Cooper S, '09 Volvo V70 D5
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Apr 27, 2006 13:55:17 GMT
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I believe a rich idle mixture will raise the Idle RPM. Exactly the same problem I'm having with my fastback at the moment.
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Apr 27, 2006 14:18:46 GMT
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Have you checked your butterflies are fully shut without your foot on the pedal? Next step is, as Chris says, checking your mixture
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Apr 27, 2006 15:12:00 GMT
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I'd suspect a rich mixture too.
*edit*: Is this the Golf that just passed its MOT? I'd have thought if it was running very rich the car would have failed. At the very least you should have the emissions test printout which would give you an idea of the state of tune
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Last Edit: Apr 27, 2006 15:15:20 GMT by BenzBoy
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Apr 27, 2006 15:20:58 GMT
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Good call, check your printout figures
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Apr 27, 2006 18:01:02 GMT
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That arrow looks like it's pointing to the throttle balance bar between the two carbs. You might be opening the throttle on the other carb by turning that.
Also check there are no air leaks between the gaskets and the carbs and the manifold. I've found them notoriously rubbish at sealing properly.
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Stu
Posted a lot
Posts: 2,913
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Apr 27, 2006 19:45:25 GMT
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That arrow looks like it's pointing to the throttle balance bar between the two carbs. You might be opening the throttle on the other carb by turning that. Also check there are no air leaks between the gaskets and the carbs and the manifold. I've found them notoriously rubbish at sealing properly. Good point, yes, it's the balance bar stop screw thing that I'm adjusting. As for leaks, now you mention it, I'm sure the idle was a bit lower before I started messing with the manifold the other week to plumb in the vacuum take-off so I may well have created a leak somewhere - I will double check. Not sure if I got a print out of emissions at the MOT station, don't think I did actually as they were on 'emergency certificates' as the whole country's MOT computers were down that day (Tuesday). I ended up with a handwritten certificate and have to go back for my proper 'computerised' one so I will ask about emissions then. As an aside, I adjusted the throttle cable a bit to see if that affected the idle, it didn't but it has improved the 'kick down' feature - it's quite alarming when a 30 year old 3-speed Golf 'kicks down' to second gear when you floor it at 60mph! Bwaaarrrppp! ;D
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Last Edit: Apr 27, 2006 19:46:42 GMT by Stu
'89 BMW E30 325i Sport, '04 MINI Cooper S, '09 Volvo V70 D5
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Also check there are no air leaks between the gaskets and the carbs and the manifold. I've found them notoriously rubbish at sealing properly. it's quite alarming when a 30 year old 3-speed Golf 'kicks down' to second gear when you floor it at 60mph! Bwaaarrrppp! ;D[/quote] Winner!
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Stu
Posted a lot
Posts: 2,913
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Apr 29, 2006 15:35:33 GMT
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Hmmm... well, I checked all the manifold to head bolts and also the ones that hold the carbs to the manifold, some where a bit loose so tightened them all up.
I still get a high (just over 2k rpm) idle though once the car has warmed up so something else must be wrong. The mixture and all other settings haven't changed I don't think, and I'm sure it used to idle lower than this before I started messing around connecting up the brake servo vacuum take-off a few weeks back.
Any more ideas? Any way to DIY check/adjust the mixture or will I mess it up?
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'89 BMW E30 325i Sport, '04 MINI Cooper S, '09 Volvo V70 D5
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I still suspect air leaks if it only does it when hot. Mine used to do that all the time and it used to sort itself with a set of new misab spacers (the thick ones between the carb and the manifold)
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Stu
Posted a lot
Posts: 2,913
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Cheers Jonny, I will check for leaks again then and possibly replace those spacers if I can get hold of some. They seemed to seal by means of large rubber O-rings on both sides, one towards the manifold and one towards the carb, so perhaps they are past their best?
I will investigate as the 2k plus hot idle is bugging me now, and probably using a lot of fuel too!
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'89 BMW E30 325i Sport, '04 MINI Cooper S, '09 Volvo V70 D5
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No doubt playing havoc with your autobox as well! Amen to the air leak, or there's summat else goin' on! ;D Should be an induvidual idle adjustment on each carb though? Might be worth balancing them
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Last Edit: May 1, 2006 18:24:15 GMT by Lewis
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Hmmm... well, I checked all the manifold to head bolts and also the ones that hold the carbs to the manifold, some where a bit loose so tightened them all up. I don't know a great deal about twin sidedraft setups. But arent the carb to manifold bolts supposed to be set at a very low torque to stop the thackery washers compressing and then causing vibration in the carbs
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Stu
Posted a lot
Posts: 2,913
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Should be an induvidual idle adjustment on each carb though? Might be worth balancing them I thought there would be an individual adjustment too, I must get a book on Dellorto's as the carb book I have seems to cover everything but these and I don't want to cock it up, runs quite nice idle aside
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Last Edit: May 1, 2006 19:10:45 GMT by Stu
'89 BMW E30 325i Sport, '04 MINI Cooper S, '09 Volvo V70 D5
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Stu
Posted a lot
Posts: 2,913
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I don't know a great deal about twin sidedraft setups. But arent the carb to manifold bolts supposed to be set at a very low torque to stop the thackery washers compressing and then causing vibration in the carbs You may be correct! Hmmm... I wonder if I've overtightened them now? Oh dear. Still I'm learning as I go along!
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'89 BMW E30 325i Sport, '04 MINI Cooper S, '09 Volvo V70 D5
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Stu
Posted a lot
Posts: 2,913
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I've just been browsing for more Dellorto info, and possibly a book to buy to learn a bit more about them - Jonny, what book is it that you use? Anyway, found this site: www.racecar.co.uk/dellorto/Which seems to have some very good info about how to set up the idle etc. It seems the screw I was adjusting (no. 4 in this pic) isn't actually the idle adjustment but the balance lever adjuster as someone mentioned above. The idle screw seems to be no. 2 in this pic instead so will have a look at that to see if it helps. One theory I have thought of is that maybe there was always an air leak when it was set up previously, and now I've tightened everything up and removed the leak the mixture has become over-rich so causing a high hot idle - does that make sense? In any case, on an A-road and motorway run last weekend the car averaged around 27mpg cruising at 60 - 70mph, which with a 3-speed 'box surely means the tuning isn't far off! Better than I expected to be honest!
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Last Edit: May 5, 2006 11:24:21 GMT by Stu
'89 BMW E30 325i Sport, '04 MINI Cooper S, '09 Volvo V70 D5
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Stu
Posted a lot
Posts: 2,913
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'89 BMW E30 325i Sport, '04 MINI Cooper S, '09 Volvo V70 D5
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27mpg sounds alright to me - but then I do have a tendency to drive in an enthusiastic manner ;D
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Stu, yeah you're not supposed to crank the bolts up tight because the fuel foams up in the float bowls. There should be either spring loaded washers under the nuts and you tighten them to the point that the spring just bottoms out or you have thackery washers which are rubber figure-8 donuts sandwiched between two cupped washers. You tighten these until the two washers just meet. I've generally found them all to be curse word and it doesn't give a good seal at all like that and I end up cranking them up tighter to seal them.
Right, when using two carbs there is only one idle speed adjustment screw as labelled in position 2. The screw on the balance bar is to adjust the butterflies in the second carb so that they are in the same position as the first carb. The ONLY way you can do this is with a synchrometer so you WILL need one of these. You set a high idle speed with the screw on the front carb, take a synchrometer reading from the front pot of the front carb and adjust the balance bar so that the front pot of the second carb matches. You then read it again, adjust again and soforth until the two pots flow the same. Then you can reduce the idle speed to normal with the screw on the first carb.
Idle mixture is ultimately governed by the idle jets but there are the 4 screws pointing upwards at the base of the carbs so that you can adjust +/- a bit. Screw all four in until they bottom out. Then unscrew them all 2.5 turns which is your base point. flip the throttle a few times and note how it responds. You want to lean them all off by the same amount each until either the engine starts to spit back when idling (in which case it is idling too lean) or until it spits/coughs/splutters when you open the throttle a bit. Then you should rich it back up by a 1/4 of a turn and job is done. Each time leave it to settle for a few seconds after you have adjusted the screws.
Then you can check the timing.
My book is called How to Build and Power Tune Weber and Dellorto Carburettors by Des Hammill in the Speedpro series. I really recommend it as it will teach you everything you need to know about your carbs. I haven't bothered rolling roading a car yet as this book really gets you to know what it's doing the old way.
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Last Edit: May 5, 2006 13:25:13 GMT by Deleted
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i thought a lean mix would make it idle higher, this is what i have experienced with 2 different cars and also a goped. Mind you, what do i know! haha. Look online for a tuning guid, it will show you the right screws to adjust. You can always take them all off and sell the carbs and manifold to me....
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