Tachometer jumps and timing moves

[Hodgy92maverick]

Hey all, My tb42 Mav carby model is missing, tachometer jumps and when I time it, the mark moves under the light.
I have replaced
New carby
Iridium plugs
10.5 mm leads
Dizzy cap
Extended rotor button
Dust plate in Dizzy
Pertronix electronic ignition
Flame thrower coil
Replaced all wiring and electrical clips around Dizzy.
It does run a bit better after all this was replaced but, still misses and tachometer jumps.
I'm hope the new Dizzy I'm getting will stop the problem. Anyone got any other ideas

[mudski]

Yeah I can only think the the shaft in the dizzy is worn out. If there any play in the dizzy shaft? I remember the old 308 in my HJ panelvan having similar issues and it was the dizzy. Jumping tacho has got me confused though. Does the tacho pick up a signal from the dizzy to work?

[Turtle_au]

Moving timing mark indicates problem with advance mechanism. Either mechanical advance (sticking or broken spring), or vacuum advance (leaking vacuum line, hole in diaphragm or sticking linkage)
Tacho will jump because it just goes off the time between sparks which will be totally eratic at the moment.

Sent from my SM-T355Y using Tapatalk

[Yendor]

Try disconnecting the brown plastic box that should be mounted on the inner guard near where the original coil was mounted. It should look this.

[dom14]

Try disconnecting the brown plastic box that should be mounted on the inner guard near where the original coil was mounted. It should look this.

Ballast resistor?