Idling- not my van's strong point-ideas?

[Bluehaze]

My grey used to idle like it had a hot cam, turned out one of the spark plugs were sparking to ground on the outside. I could hear the arcing on a plug, and under low light could see the blue arc at the edge of the plug boot. Only at idle.

[fingers]

thanks gents for all your input.

The faster idle adjustment has helped-it's about 60-70% smoother at idle , there didn't seem to be any manifold leak based on the wd 40 test and Trev your suggestion is my next port of call.

cheers
m

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Hey Matt did you adjust the fuel mixture as well as the idle speed ..........Fingers

[MeFB]

Some people make the mistake of using the idle mixture to adjust the idle speed, lean = faster idle, rich = slower idle, but this isn't the way to do it as you'll have poor pick-up and idle. The screw on the carby's throttle lever should be used to adjust idle speed. The mixture is a separate adjustment. The idle mixture and the idle speed need to be adjusted together as idle mixture affects idle speed.

My guess, and it is just a guess, is that the reason your choke isn't making much difference to your idle speed is because your idle mixture is too rich to start with.

Here's an extract from Harv's most excellent guide (hope you don't mind Harv):

To set the idle speed and mixture:

1. Warm the car up to normal operating condition. Check the choke is off. Leave the air cleaner in place.
2. On automatics, the transmission should be in DRIVE (D) with the handbrake firmly engaged.
3. Fit the vacuum gauge to the inlet manifold and the tachometer (where available).
4. Adjust the slow idle adjusting screw (54) until the engine idles at 480-520 rpm (check with a tachometer, timing light counting or “by ear”).
5. If you have a vacuum gauge, adjust the idle needle valve (59) until you get the highest vacuum
possible (this should be between 17”-21” Hg, or 60-70 kPa, or 8-10 psi). This can be difficult if the vehicle has a large cam (high valve overlap) as the vacuum at idle will fluctuate. In this case, adjust the idle needle valve (59) until the tachometer reads maximum rpm. If you don‟t have a vacuum
gauge or tachometer, turn the idle needle valve (59) slowly inwards until the engine starts to run
irregularly. Back the idle needle valve (59) outwards until the engine begins to “roll”, then inwards
again until the engine runs smooth.
6. Check the engine speed again, and repeat steps 3. and 4. above until a satisfactory idle is achieved.
7. Remove the tachometer and vacuum gauge and refit any vacuum lines that were disconnected.If a rough idle persists after the mixture screws have been adjusted, check for vacuum leaks. These could result from unplugged vacuum fittings, carburettor flange gaskets that were torn during installation,cracked lines or loose bolt/screws. A quick way to check vacuum leaks is to spray WD40 in the suspected area with the engine running – if the engine speed increases, there is a vacuum leak.

[MeFB]

Alan I know that's what's in the workshop manual, but it's a hell of a lot more complicated than my suggestion above 'turn screw in till engine stalls and turn out 1.5 turns'

Tim

Right you are Tim. Can I just add that the screw you're talking about is the idle mixture screw, and that once you've done the 1.5 turns, then the idle speed should be adjusted with the idle speed screw.

I know this is obvious to us old pharts, but maybe not to everyone