My 8v has started to judder (done it twice in a week) and lose power.
The 1st time it was started first thing in the morning, and made a bang like it was backfiring

and just wouldn't rev. I popped the bonnet, checked/fiddled with the HT leads, tried again and she fired up lovely and ran like a dream for 3 days, then it happened again this afternoon, doing the school run it started juddering again (no pop/backfire) so I stopped, switched off, fiddled with the HT leads again and off we went.
I replaced the leads, dizzy, rotar arm about 10 months ago, could they be failing already? (only done 2k in her since then) or could it be something else??
Help much appreciated