Hi all I've been recommended here by the Jaguar breakfast club.

Hi some help please. Took my XJ6 out yesterday for a run all was good started up fine engine got up to temp then on the back home i did a u turn at a mini roundabout and it died started up agian first time put it in drive and it splutterd a few yards and died, I tried turn the mix up/down same thing i tried putting the revs to 1000 same thing even if I applied to much gas ( foot to the floor) in park revs would stay the same then die, yet normal on the pedal and it was fine. Anyway after an hour i gave up called the AA. When the AA got here the car started fine like always and drove home perfectly. I've drained the fuel and well put fresh stuff in but i dont want to jump to conclusions and blame old fuel as ive had missfire under load before but normally at the start of a drive.
it has had a manual choke conversation.

Check the temperature of the coil, sounds like its overheating and cutting the spark. When the coil cooled off it fired up again?

Yeah it was the fuel mix i was playing with to just try and the car off the busy road i was on i put it back to the original setting. The car would start up and idle fine but as soon as i put it drive it would splutter a few feet then die but start straight away when i turned the key. In neutral it would rev fine but put it in gear and the load of selecting drive caused it to splutter and cut out. I was thinking about changing the coil just in case it has a intermediate problem.

SU HS8 carbs

o1xjr thanks for that link I've been thinking about changing to a "123 ignition " . Did you have the same issue with fireball ok in neutral but in drive/reverse misfire