Hey Max ,i wont add much to this Jaffa has got most of it spot on .
Normally this issue is vacuum related , however ive rarely found a bottom bearing at fault as its well protected by the flywheel.
The starter o- ring is a regular offender , even if it looks ok replace it if its slightly stretched or pinched it will cause trouble, there is also another oring on the starter shaft that is often forgotten.
Another thing to check is the springs either side of the diaphram check to make sure someone hasnt been in and messed with them , trimmed them ect , also that they are in their right positions , small spring on the cam side and large spring on the cap side.
I had issues with a g4/lm this week but on the older full crank engine i had to make a post for idea's from the other guys turned out i had a leaking top crank seal!
stick at it !
cheers tomo
Last edited by tomo4192; 24/10/13 05:50 AM.