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Nov 28, 2012 13:09:24 GMT
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The weber carb on my CVH won't idle these last few days with the cold weather.
Starts fine. Has a manual choke. Even when warm and up to temp, it is also hunting up to 500rpm at times. only been since the cold weather got here.
I have either having to run with the choke on (not fully), turn up the idle speed using the idle screw, or "pedal" the car with lots of throttle blipping.
Main problem is when coming to a stop. Even when coasting in neutral to a stop. As I press the brake the revs drops as the speedo drops. Revs get to 1200 - 1000 and it stalls, unless I catch it with the throttle or clutch.
I have checked for air leaks, cannot see / hear any.
Taken off the filter, and I can see at idle the fuel is literally just dropping, drop by drop ( a little quicker than once a second)onto the butterfly, when on idle. Soon as I open the butterfly / throttle the venturi effect starts to atomize the fuel correctly.
I am quessing that in summer at idle the fact the fuel is just dropping into the card, is not an issue, as everything, the carb body, the air temp is nice and warm and the fuel atomizes fine.
In the colder weather the lumpy idle and "hunting" is due to the fuel "dripping" into the carb, and then dribbling over the butterfly into the inlet. so the fule is not entering the engine at a very constant rate (and possibly mixture)
beside raising the idle speed, I don't know what else I can do? richen up the mixture? But the mixture adjustment screw on my carb is "capped" off. I have tried digging out the material with a screw driver with no luck.
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Last Edit: Nov 28, 2012 21:05:31 GMT by br1gg5y
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Nov 28, 2012 13:27:23 GMT
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If pressing the brake pedal is making the idle change, your brake servo is knackered. Does it test properly? 3-8 pumps before going hard with the engine off, then the pedal sinking beneath your foot as you start the engine.
Other thought is that the idle jet is blocked - this always makes an car hard to drive, as the idle jet not only provides the idle mixture (via the volume, or mixture, screw) but also the first part of the progression as you open the throttle.
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Nov 28, 2012 20:26:20 GMT
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If pressing the brake pedal is making the idle change, your brake servo is knackered. Does it test properly? 3-8 pumps before going hard with the engine off, then the pedal sinking beneath your foot as you start the engine. Thanks, To be clear I can't make the revs drop by pressing the brake whilst the car is moving or stationary. But the quickly dropping revs are always when braking coming up to a junction or give way. I tried your test and the pedal sank about 10mm(20mm Max) when the engine started. That sound ok? or would you expect the pedal to sink further. If I switched off the engine and immediatley tried to repeat the test, the pedal did not sink.But I am guessing that is because the pressure (or indeed vacuum) is still present within the system. I am leaning towards blocked jets. But how to remove,them and clean? suppose to answer that question. I need to confirm the model of the carb, will work on getting that information. |
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bortaf
Posted a lot
Posts: 4,549
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Nov 29, 2012 13:00:24 GMT
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check the vac lines havn't fallen off, they loose grip in the cold weather and fall off the alloy stubs they sit on  allways start easy and work inwards lol  |
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R.I.P photobucket
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Nov 29, 2012 13:29:36 GMT
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If there is no tickover at all? even when hot? and the dead stop coast then it would suggest a dead/stuck ISCV. These are held in place with a ten mil nut, you'll notice the plug down on the right hand side(as you look at the carb from the front). It may even be that the plug has come off and needs put back on. If your close id take a look as had to setup tens of wonky old carbs
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Nov 29, 2012 21:31:46 GMT
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Nov 29, 2012 22:08:14 GMT
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whats the tickover RPM? The size of that filter is screaming to me that its under fueled, given the size of the filter its weakening the mixture. there is a small flat head screw on the rear of the carb that allows for adjustment. Where abouts in the world are you? as its easier to sort out a problem when you can get your hands on it.
Edit ment to say riching the mixture not weaking
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Last Edit: Nov 29, 2012 22:10:32 GMT by chrism1
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Filter size doesn't look to be an issue - and anyway, filter restriction only really becomes an issue at high revs and loads. It looks as though it would benefit from a good clean and re-oil though.  Also, 2 questions: 1) What make is the distributor? 2) Have you had a timing light on it and checked for ignition 'scatter'? |
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Last Edit: Nov 30, 2012 0:01:49 GMT by jrevillug
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I'm in the northwest, Wigan to be precise, will have to check the make of the dizzy, and not checked timing for a while, will do that also.
I agree a service of the carb could do no harm. But without establishling the model I can't go and purchase a recon / service kit.
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Nov 30, 2012 10:04:44 GMT
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Ok I am now convinced I have a DFTM  and looking at that I can remove all the needles / jets and clean them, without takibng the whole carb apart, which I don't want to do as I suspect all the gaskets are brittle. Need to take off the air filer and see if I can see a model number on the top of the carb. Then I can get a rebuild kit, so I will attmept to clean the jets this Sat. What do you mean when you say re-oil though? Also from the diagram I can't determin which hole part number 6, the idle mixture screw sits in. The problem is that side of the carb faces my bulk head on my car and it's hard to see. So better to have an idea where to look before hand |
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Nov 30, 2012 11:05:00 GMT
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Assuming its a 1600 cvh, then the filter is right, however if its a 1400 then its al ittle large
taking a DF apart is easy enough, its mainly flat head scews just remember what order the jets go when reasembling, It could be a simple fix as a loose jet but I'm still going with a dodgey mixture
By re oil what JR means is the filter could do with a good clean and treatment to keep it subtle. K&N do a cleaning kit for around £12
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bortaf
Posted a lot
Posts: 4,549
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Nov 30, 2012 13:35:28 GMT
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how can the filter be too large sounds to me more like carb icing cos there's not warm air feed to the filter |
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R.I.P photobucket
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Nov 30, 2012 20:04:16 GMT
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I'd agree with bortaf, could be as simple as carb icing. on my polo I use an open k&n filter in summer, but in winter I use an enclosed filter with a warm air feed from the exhaust   |
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Nov 30, 2012 22:13:00 GMT
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well made a start tonight, it would seem weber did not want anyone fiddling with the idle mixture screw as the recess is filled with some metal / solder  I am soaking the needle jets, one of them is particuarly blocked, as it seems. The built in fuel filter seemed fine though     the inlet manifold seems nice and clean  it was fine last winter with the K and N filter with no hot air feed from the exhaust. I am also in the process of cleaning and re oiling the filter |
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well, a good clean, re oil of the air filter, and 1/2 a turn out (richening) the idle mixture, has definetly improved matters. Just need to try it tomorrow morning after acold night, and see if further richening is needed
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Chances are the car will now use less choke when cold as its now getting a better flow.. You'll know if it's ever over richened as you'll get a whiff of petrol from the exhaust. You ideally want a warm tickover idle of around 750/900rpm. One thing to consider is to also start to run an additive every few tanks,modern fuel is full of ethanonl which damages the brass workings of the carb and in some cases has been known to gum the jets up with metal debris
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hkr91
South East
Posts: 559
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Grab some old brake cable from an old bicycle. Cut a piece off and use the strands to clear the jets.
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hkr91
South East
Posts: 559
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Any update? Has it cleared up?
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Grab some old brake cable from an old bicycle. Cut a piece off and use the strands to clear the jets. No. Steel wire in jets is a really bad idea - they are high-precision, very sensitve to wear, and even cleaning them out with wire once can damage them and cause over-rich running. Far better to use a combination of solvent and - if really stubborn - the bristle from a nylon brush. I tend to use an old toothbrush. |
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Dripping fuel onto the butterflies at idle can indicate worn needle and seat or float level too high. It could also relate to worn throttle shaft allowing lean mix. From all the carbs ive built iwhat saves frustration over and over again is to strip the carb down as much as possible. Unless necessary don't fool with the butterfly screws.Then soak in lacquer thinner making sure that only non rubber parts are in the thinner. Wash with hot soapy water, the blow passages with compressed air every orifice and air tubes etc. I rebuild spraying everthing internally with wd 40 in case I let the carb sit. 2 turns on idle mix screw to start, get engine hot, check timing as per spec then adjust 1/4 turn on the rich side of peak idle speed, highest vacuum (using vac gauge) .
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allways start easy and work inwards lol 
