Mystery cause of sticking inlet valves on Mk II engine.

[paul.jameson]

I managed to do over 50 miles today on the Healey, mainly at 50mph-ish, ending by riding back up the steep lane to home with the engine then ticking over for a few seconds before I could switch it off to freewheel in down the drive. Photos of No 2 plug are below. All comments on the colour(s) would be appreciated.

[MarkO]

Looks OK to me. A plug chop may be more of an accurate indicator - though it is a faff about. Basically as below.

1. Get new spark plug(s)
2. Warm up motor to operating temp on old plugs.
3. Install new plug(s).
4. Accelerate through all gears to top gear with throttle pinned.
5. When you hit the top of the top gear, pull in the clutch and if possible kill the engine with ex. lifter. Not sure how you do that on a SQ4!
6. Remove the spark plug(s) and ride home on the old plug(s).

7. Hold the new plug in a vice and use a hacksaw to cut the threads
away from the centre electrode. The chop bit!
8. You should see a brown 2mm "smoke ring" at the base of the
white centre electrode if the fuelling is good.
9. if the smoke ring is darker than chocolate brown or taller
than 2mm, you're rich. If the smoke ring is smaller than 2mm or lighter than chocolate
brown, you're lean.

Having said all that, I've only done it once or twice, but it did seem a reasonable indicator. Otherwise, I simply observe the exhaust and whether it bogs down on throttle to see if it is running rich.

[chris.shearwood]

All comments on the colour(s) would be appreciated.

Hello Paul,
That plug looks fine to me. If I found a plug looking like that in either of my two bikes I'd stop fiddling with the carb right then!
Chris

[nevhunter]

Looks good to me Paul. My cruise test is on a longish hill , IF it goes a little better when you back off the throttle slightly she's getting a bit lean. Idling is always rich or it's erratic and harder to start. Rich and the oil will get darker quicker. Finally check your MPG figures. If the plugs go very white the insulator is getting very hot and it might "pinK" or detonate on load on take off, from the lights. IF it's a question of PLUG suitability I'd rather err on the cold side. Nev

[david.anderson]

When tuning by plug colour you should start with a new plug. The plug shown may have done a lot of work. I have to disagree with the previous posts. Looking at the plug (maximised photo) in general for unleaded fuel the amount of soot on the sparkplug base ring and inside the metal body, and electrode indicates a too rich mixture. A very light soot ring on the base ring is all that you want to see, with no soot on the electrode. There is also a large glazed deposit build up on the ceramic insulator and electrode which again can indicate a rich mixture (rather than peppering which is lean). The electrode strap should be clean to tan.
The spark plug colour would be indicative of the throttle opening at 50mph (possibly ¼ throttle) and should not be main jet. But I know nothing about the stages of a Solex carb.
And are all plugs the same.
While you never want to run a square 4 lean due to the extra heat, that is too rich for me.
David

Edit
oops. for some reason i was thinking of your pre war 4, not the Healey which is fitted with an SU and not a Solex. So I would be leaning the mix with the adjusting nut at the bottom of the SU, which of course leans the mixture right through the range. If that is not right then possibly try a different needle as you have suggested. The best way to retune is on the dyno as most dynos also have an exhaust sniffer (exhaust gas analyser). The exhaust gas analyser will give precise readings right through the throttle opening range. It should take some of the trial and error out of needle selection.

[chris.shearwood]

Some useful plug photos (I'm not sure of the differences between leaded and non-leaded fuel use) :
http://www.dansmc.com/Spark_Plugs/Spark ... talog.html

[JohnnyBeckett]

hi i would just keep on running it in before i start worrying about how the plugs are running, they will keep changing until the engine is run in, then i would think about adjusting it