Defender 3.9 v8 problems

Hi I am havin problems with my v8. It Was running fine, because I am going away off roading for a week I thought I would give it a birthday! I changed the ht leads dizzy cap and rotor arm with powerspark kit, that was causing it to miss like mad. So I bought a genuine cap rotor arm and magnecore blue leads, when I fired up it ran fine and revved with no hesitation or missing. I thought job done! When I taken up the road for test its sluggish on low to medium revs seems to be tappy when you get to high end it's almost fine. I then changed all back to original and it's still the same I have checked all vacuum hoses and have changed the air flow meter nothing makes a difference. I changed plugs a while back and it was fine took them out they were slightly white I put the old ones back in and that made no difference either. I'm stumped I don't know a lot about v8s and I appreciate any help thanks.

When you changed the rotor arm did it come off easily? If you had to yank if off and the center spindle came up with it you may have disturbed the advance springs down in the bottom of the dizzy. This could cause the problems your describing - it happened to me

MattMatt said:

When you changed the rotor arm did it come off easily? If you had to yank if off and the center spindle came up with it you may have disturbed the advance springs down in the bottom of the dizzy. This could cause the problems your describing - it happened to me

Click to expand...

Yes as ****ty plastic retainer

MattMatt said:

When you changed the rotor arm did it come off easily? If you had to yank if off and the center spindle came up with it you may have disturbed the advance springs down in the bottom of the dizzy. This could cause the problems your describing - it happened to me

Click to expand...

Hi Matt, that may be the case! How do I reset it? I have also done the timing and it is marginally better but not perfect

Ok - you have to take it apart.

Before that, looking from the top (from memory) the rotor arm goes clockwise. You should be able to lightly twist it against the AR springs - twisting back anticlockwise (retard) should be against the stop and twisting it forward clockwise (should be advance) which brings the springs into play. If there is not much resistance or the rotor arm doesn't return to it's normal position when released is a pointer to the springs not doing their job. I am not near an engine right now so I might have my clockwise/anticlockwise mixed up but you'll get the drift. If I have, someone will be along to correct it I'm sure

This is the advice from RPI Engineering

First, remove advance vacuum pipe from intake and check for positive vacuum when throttle is applied.
Check positive vacuum will pull distributor advance whilst also checking vacuum module is not holed (when sucking the pipe, the base plate of the distributor should rotate anti-clockwise about 15 deg.).
Check condition of rotor arm for signs of damage or arcing, also check cap and clean contacts (better still, fit new).
Check rotor for free play, there should be none, both rotationaly and side to side.
Check rotor will turn clockwise through about 20 deg, and smartly retract back to its home position under good spring tension.
Distributor output is known to be weak so upgrading with our Spark amp is recommended. (see below).
Replace plug leads, preferably with Magnecor. Use good quality Plugs such as NGK BP6ES, avoid fancy plugs as they don't normally last long.

Taking it apart is not hard but just be careful! and note where everything goes. SimonBBC is a good source of spares including the springs.

Sounds like a duff dizzy to me

RPI in Norfolk have a job lot of ex-MOD genuine Lucas distributors for 75 quid a piece.

Just ftted one into my disco - lovely.

Whatever you do do not be tempted to purchase the Britpart alternative - with the blue cap - in my experience they cause more problems than they solve.