If in doubt DOT5, as it is used in most motorcycles and is less prone to water absorption.

Worth a shot, if it fails, zigzag springs and a bit of foam or an inner tube partially inflated in a case?

Commentary for mine Jim, sorry I can't make it :-(

" Well the cyclekart known as slippery Jim is nowhere in sight! Literally nowhere to be seen at all, added stealth technology by the driver painting his kart with blended octopus and chameleon corpses  makes it hard for the opposition to see just how well he's doing! His driver skillfully avoids all photographic evidence as he probably rounds the bends with great aplomb and not much of a to-do, we think. The plucky three wheeler is powered by three hamsters in a wheel coaxed gently around with a copy of play-hamster on a string at idle and uses a vicious pixie dressed in bondage gear as a cox when the accelerator is floored - we hear he may acquire a mystic supercharger for future events. Apart from enjoying Viking re-enactment and the illegal transportation of small Australian birds hidden in lycra, the driver, also known by the alias Jim, pingu (for some unknown reason) and Ivar Thor-Heilbo, has been driving for nearly a season and is gaining momentum - slowly, and we mean slowly"

Slippery Jim is proudly sponsored by Albert Fegworthys' seaside emporium and general knick-knackery.

Rhys, agreed. But now Denny is setting traps over there by showing monster bored out 212 cc things to 263cc and saying that is he wasn't retired and had the desire he would have a go at it!

". I know I would if it weren't that I'm a long time retired guy who tain't got the geedis now a days.
dg "

A man of contradictions, as we all are.
My point was about reliability. I will say that as many times as I can. If you add a component that costs, at most a hundred bucks plus postage - eighty bucks the numerous times he has a sale during the year I have been watching him and it saves you buying one billet con rod, let alone all the other components you have to use to get your engine to such power as to muller two con rods in the first place and whatever else you might damage along the way, is it a false economy not to have one?
An example. A highly tuned but unreliable vehicle is fast for three laps then stops for tinkering or goes back on the trailer. This happens quite a bit. Some people travel great distances to attend events, even pay for hotels to stop over, track fees, fuel, food out, (BEER  ) What price reliability? One meet like that and I would burn through more than a hundred bucks with a bad taste in my mouth and be no wiser with a list of jobs to do in the garage when I got home.
Most of our received wisdom on engine tuning is from the kart scene. Small wheels, light karts, high revving engines with many rules of what you can and cannot do to them. It has become prescribed and set due to rules. Kart tuners use these rules to wring the most out of the engines within the rules and the life of these engines is measured in hours with an engine not reaching its full potential for a few hours then lasting a season and getting worse or breaking.
I argue that perhaps, given the only rule we have is 10hp max -again, a sensible rule that ensures we can insure them and be relatively safe, keep the hobby accessible to new entrants and stop an arms race of bought components that can easily triple the price of an engine whilst making it less reliable- We should look to reliability and the fun we can have within the power we are allowed. I would not like to utilise all 10hp around a tight and twisty track in a three wheeler and didn't- The goal should be to broaden the power band to stop machines bogging down in the corners as much, keeping the machines drive-able, whilst building for reliability so we get to enjoy many laps.
If I have achieved this I am not sure yet but that is my aim it could still prove unreliable or unsuited. (Notice how I have not yet published my findings so far on the CDI thread I started?) I am, like most of us, a tinkerer. If I fail I try again. I first had the idea looking at what the vintage motorcycle people do to make their bikes a little less likely to snap your leg on starting and be more reliable - hence the CDI kit- Since putting it on, I have also looked at how to knit one out of bits cheaply available off the internet that might, if it works, get the price down to about £30. (two rounds of drinks for four up north, bloody expensive!).
I hope that fully explains my thought on this Rhys. It is not intended as an arms race for speed or power. It is intended to keep the cyclekart usable and reliable. If it does not do these things I will bin the idea as, as yet, it is an experiment.

Are Gemini prices without VAT and delivery? Those are inclusive

Well the trailer and the BSA made it to Stretton without incident and a grand day out was had.
The BSA proved reliable on the day, the new steering rack was a joy to use compared with the old Pitman arm set up and the tweaks to the geometry seemed to work.
The CDI system worked a treat with smoother power delivery across the rev range and a quieter engine. As before when I have driven it, it never felt like it was at its limit for power but I doubt I have topped 10hp with it. (I have no dyno) For this circuit, the power was more than sufficient.
I mostly kept it on three wheels, tight corners and too much power on the exit at slow speed was the cause of wheel lift each time. (same corner)
I was not quick. I suspected that the lack of a fourth wheel might make me a little slower and this proved the case. However, if you multiplied our lap times by our wheel count then the BSA was very near the other cars on the few timed laps we did.
As always I come away wanting to tweak a couple of things, less so than last time though.
The spark plug after a good thrashing shows the engine to be slightly lean - I will re jet the carburetor to the next size up main jet for next time.
I need a couple of touch ups on the paint on the spinners (oops) and the hood ornament 
But that is about it. For a first test with corners I am very happy with "Slippery Jim"

... I bet it's not William 🤣

Well I'm here 😁