I've got a 1.8 cabby with a webber fitted, I took it for it's MOT recently and it failed on emmisions[:^(] , 7% or something like that, so after searching on here I went and bought a colourtune kit from halfords and gave it a try. I can get the flame to go orange which indicates it's too rich, I turned the screw to lean the mixture off, my plan was to get the flame white (too lean) and then set the mixture somewhere between the rich and lean settings in the hope it will pass it's MOT. My problem is that I can't get the flame to go white, it's now half a turn from been fully screwed in, and still no white flame, it also still stinks of fuel. It starts and drives without a problem, and theres no black smoke. Any ideas what could be causing this?
I'm guessing it has passed on emissions in the past ? Is the idle speed screw unwound enough so the butterfly is fully closed and not by-passing the idle circuit or is the throttle cable stopping it from fully closing ? Plus make sure the choke is disengaged. Failing that you could try going down a size or two on your primary idle jet. Incidentally, I'm planning on getting a colourtune for a similar Weber problem on my 5.7 Chevy ski boat engine - can't seem to get it to lean out enough at idle without being 1/2 a turn from fully wound in. /edit just thogut of somethign else - is the air filter partially blocked / restricting flow ?
I don't know the set up on a weber, but I have a similar issue with my pierburg. Although I have an OK idle and CO2 reading, when I was playing around I thought I'd try to lean the mixture a little (to see what happens with colourtune). I kept screwing in the mixture but it didn't seem to make any difference. I was wondering if the 'o' ring wasn't sealing properly letting the same amount of air in all the time. Just a thought, but maybe there's an air leak somwhere.
Is the float alright? I'd have spent the money on getting the MOT man to set it up for me rather than buying the colourtune.
I got the colourtune and set up my webber with it. From memory I think I got mine to go light orange. I though I set up correctly, although I still get a crappy 25mpg. Think Im going to have to get a garage to set up the webber properly.
What's the carbs history? Did it pass okay last MOT? Has anything been done to it since? You say it stinks of fuel - take the airbox off and under the bracket that the airbox bolts to is the breather for the float chamber - it's a flat mesh. Is there evidence of fuel about the place? The float valve is sticking open, the breather is where the fuel comes out and it will over fuel at tick-over as well as stink. Have you gone through the stock Weber setting up for the idle? As for the Colourtune you're looking for the mixture to have just gone from yellow to a vivid blue, which you haven't mentioned it doing. I serviced my Weber a couple of weeks ago and it failed the MOT on mixture - as I didn't have a screwdriver to weaken the mixture off the tester - having commented the car was well looked after - re-did the test at 2000 rpm and it passed no problem. If you can't get it sorted than it'll be worth having the garage sort it before the retest. I've used the Colourtune to do my bikes in the past but that was in the days before they tested emissions. Barkstar
Cheers for the replies, the carb was fitted to the car when I bought it so i'm not sure if it's ever passed a MOT with it fitted, before it went for it's first MOT attempt I set it with the colourtune to the vivid blue flame as you say (I was also able to get the white flame too), however, this ment it failed the MOT at 7%, when I got it home I had a look around and found a vacume leak on the servo pipe one-way valve, so I swapped this for a good valve and now I can't get the lean white flame to appear.[:^(]
Found this, which may explain better: While trying to keep the engine at Idle, view the top of the Colourtune Plug window, (best done in a darkened Garage, or in the street at Night. If the Colour is predominantly Yellow, slowly unscrew the Idle Mixture screw, until it turns Blue. This will happen suddenly, and the engine speed should increase as the screw is moved out. You will probably notice the occasional Yellow Flash, but the colour should be blue most of the time. If when you start the colour is already blue, then screw the idle mixture in until it turns Yellow, the turn it out until it turns blue again. Its important to stop when the colour has just turned blue, as if you continue, it will stay blue, even though the mixture is becoming more and more rich. The ideal Colour is described as Vivid Blue. Barkstar
