So to recap where I got to:
I checked the float levels using banjos and they were dead on, thanks to ZTherapy!
The engine developed an intermittent and random “miss” - I spent DAYS of my life and £££s troubleshooting the electrical system and replacing components.
The 123 ignition plasma ball turns out to be a rookie error. In the 70’s with lower voltage coils it was OK to unplug leads and crank the engine, but with the flamethrower pushing out 40Kv it’s going to find a path to ground and this test method is not recommended.
I then started to read about vac and air leaks and set about finding the issue.
This is an interesting read:
https://mechanicbase.com/engine/vacuum-leak-symptoms-causes/
Here’s the text of another post I did on the subject of finding this leak:
With the engine running, I used an unlit propane torch around all the areas where it could possibly be leaking. Nothing!
Then WD40 on the same areas. Nada!
Then water mist sprayer and guess what? Zip!
Next, I got a length of 18mm ID rubber hose and listened around the carbs and manifold area because the rear carb I thought was whistling loudly. Well, I found that both carbs are doing it and it was mainly at the mouth where the two small holes take air pressure to the piston. Hole 5 below. As I understand, SU carbs do make a high pitched sound without the air cleaner on.
Next up, I took the domes off to see if anything obvious was amiss. All I could think of was that somehow the domes are leaking.
I checked the bottom of the domes for flatness and found the rear carb in particular to be less than flat. So I got some 3mm closed cell foam sound deadening material and made a couple of gaskets.
This made it way harder to centre the needles and pistons but a bit of patience and carefulness while tightening down did the trick.
I went out to “buy some bread” and it’s a different car! The wobbly engine is a shed load smoother. The idle has also dropped over 100rpm which is a classic sign of plugging an air leak.
The AFR that previously would not budge past 15, now goes to 18+ on the overrun when in gear and cruising downhill. The idle is sitting at a lean 16 (previously 13.5-14) and cruising steady throttle AfR is between 14.7- 16. WOT when out of the reversion part of the range sits doggedly between 11.5-12.5, the latter at around 6.5k rpm. The rear wheels now squirm in 2nd at 4K rpm. This is all with the air cleaner off for troubleshooting. It would richen up a little when I put that back on. But boy does she sound angry with it off!!!
For now, I am quietly confident that the issue may have been resolved and will try to find a better solution with some plumbing rubber O rings.
The whistle though is now even louder - is this normal operation or do I have another leak that is now sucking harder? I’m erring in the side of the former but watch this space. Here’s a video of the sound ...
With COVID, my testing is now restricted to when I have to go get any shopping - especially the items not available at the local “Little Waitrose” that require me to go up the dual carriageway to the big Sainsbury’s.
I should be happy but I am itching to try out the MC needles with jets at around 1.1mm down and the original 2oz springs and the 4oz red ones I am currently using.
Moral of the story? Check intake and manifold leaks religiously before blaming other things.
BTW, I really did go out to buy bread from the next town!!!