It is also possible to sort the screws if the threads are completely gone, I fixed mine with helicoils. https://www.engineeringsupplies.co.uk/516-x-18-bsw-thread-repair-kit.html Phil

Thank you, Biturbo!    Certainly, a hand held die grinder can act homicidally, so that the minutiae of workshop practice are a lesser concern.    It seems to me that a more human reason explains the difference when it cuts nicely on one side of a hole, but climbs out, or cuts in the wrong direction on the other, and it's our (my) muscles.    The hand and wrist is a complex tool, designed for grasping a tree branch and adapted to hold tools in a wide range of positions, but not very rigidly.    The reaction to the cutting action of the grinder comes in various directions, some of which are not those where the hand/wrist's strength is greatest.     So when I find this happening, I change my grip- sometimes it works! John

Nick, do you know what thread side is in the head for the heater valve take off pipe?

I must admit on my spitfire (OK, it is "only" 25 years old! 16V so a more modern design) I run 15.5 up to 3500rpm which is 80mph or so in 5th. I have been working on TPS readings, about 15% is where I start getting a bit more serious with the fuelling, setting to 12.5 at 80-100%  When I connected an AFR to my Vitesse, it runs at high 15's at about 60-70mph, I need to have another go at the needles with a file. It doesn't hitch though, nor pink. So who knows if that is OK?

Fiddly…. And all the more irritating when you thought you were there already. Still….. perfection has its price 

Meh! Taking far longer that it should. I got the pattern made, however plan A didn't work out as I had hoped so this first (yeah, there's more) was scrap. Needed to make another but before I could get that going I needed to order more polyester resin and chopped strand mat and get that delivered, which also took far longer than 'normal' to actually arrive on, I assume, account of Christmas All the stuff here I got another pattern off the mould and started on plan B. Essentially the 'lump' needs to be slightly flatter and slightly longer. But to try and maintain some sort of integrity I am doing it in steps. Here we are mid operation... To make it longer the back part cut off and re-set 5mm back. Middle piece then has a taper slot cut so the peak can be lowered about 5mm. And the front part cut off so it can be adjusted to match the middle bit once that has been set in place. Like I said, meh!  

All good stuff here gents.

Stoichiometric is for cars with CATs. You’ll probably find you get a much better idle in the high 13s or early 14s, and it will be easier to get it to pick up crisply from idle. Lower cruising speeds (40 to 60) try for late 14s to mid 15s. Higher cruise (60+) more like stoichiometric. Full bore you shouldn’t need less than 12.5. More than that is forced induction territory, more to stop things melting than anything else. 

Useful people! I've got two proper British-made Record vices (a 23 and a monstrous 25), and both have knackered jaws that previous owners have attempted to pigeon-poo weld back on as the screws have given up the ghost.

That'll be to do with the direction you're cutting in. In one direction, the turning of the tool against the work will make it try to 'climb' out. You can control it, but as it generates more force in odd directions you'll need more force to steady it. Check out 'climb milling' for a fairly succinct explanation of it (I think This Old Tony does a video on it). Happens big time with wood routers for some reason. One direction is fine. Go the other direction and the thing will take every possible opportunity to try to kill you 🙃