12 replies to this topic

[datsun100a]

I have a feeling the dizzy on my mini is faulty. It is the electronic lucas dizzy that was fitted on the mg metro, 65DM4. The timing is set at 8deg but once I put the vac pipe back on it retarts to what looks like maybe 30deg. I am pretty sure that can't be right.

any thoughts, as the car is very sluggish at low revs and conks out sometimes.

ta

Edited by datsun100a, 03 July 2009 - 10:32 AM.

[Nightrain]

Thats just the vacuum advance doing it's stuff, it advances the timing when there's a vacuum in the inlet. ie when the throttle is only just open or closed.
Sluggish usually means it's too retarded, reset the timing to 12 degrees and that should improve matters.

But first check the mechanical advance isn't gummed up and the bob weights move freely. To do this it's easier to remove the dizzy, take out the points and back plate. Put the rotor arm back on and holding the bottom of the dizzy tightly, dont let it move. Now turn the rotor arm whilst watching the bob weights. They should move outwards as you turn the rotor arm, they should turn until they reach a small pin. If they don't get to the pin, they need cleaning out. I use a small paint brush and thinners to do this. Clean them until they move and hit the stop, once there free dry them out and oil them. Refit the baseplate points etc stick the dizzy back in and time it up again.

[mars red mike]

Its electronic - no points

[datsun100a]

it doesn't have points. i thought advancing meant moving the timing more towards 0deg?

[Nightrain]

Its electronic - no points

Doesn't matter whether it's a points dizzy or electronic, if it's a standard rover item it still has bob weights and springs ! Just remove the baseplate & pick up to see the weights.

it doesn't have points. i thought advancing meant moving the timing more towards 0deg?

Advance = How much the spark is before (advanced) top dead centre, retarding the timing moves it closer to TDC ie. your 8 degrees is more retarded than my suggested 12 degrees.

Edited by Nightrain, 02 July 2009 - 11:07 PM.

[bmcecosse]

12 degrees is quite a lot - for cold morning starts!! If the engine is pinking at all - retard it till no more pinking.

[datsun100a]

I just find it strange that at tickover, if timing is set at 8deg, as soon as i reconnect the vac pipe it advances way out to around 30degs. surely this should be happening at high revs and not tick over?

[Nightrain]

I just find it strange that at tickover, if timing is set at 8deg, as soon as i reconnect the vac pipe it advances way out to around 30degs. surely this should be happening at high revs and not tick over?

It's working perfectly, at small throttle openings the volumetric efficiency of the engine is a lot less. Meaning the combustion chamber is not been filled as effectively. Because there's less mixture in the chamber it isn't compressed as much, effectively giving a lower compression ratio, which in turn means the mixture burns a lot slower. This actually means we need to advance the ignition even more at part/light throttle openings because it takes longer to set alight all the charge and this is were a vacuum advance unit comes in. The vacuum on the inlet side created by the virtually closed throttle is used to swing the timing to give more advance. As we accelerate we open the throttle more decreasing the vacuum thus doing away with any advance created by it.

[bmcecosse]

And in doing so - it helps the idle emissions - to pass that MOT !!

[datsun100a]

thanks for the replies.

I set the timing to 12 as suggested and not much improvement so disconnected the vac pipe, engine is now running perfect and reving properly. might be wise just to leave it alone now?

[Nightrain]

Maybe, but something is not right ! What is the spec of your mini is it just standard ? If you've got a rev counter and adjustable timing light check what the timing is at 3000rpms.

[datsun100a]

engine is standard 1275 out of a late eighties mini. Just added a k&n and rc40 back box. only have a standard timing light, asked a few motor factors if they had one with the adjustor but just got laughs and giggles will need to get one on the net

[bmcecosse]

Is the idle speed set very high ? Maybe that's why it's pulling a high vacuum - and therefore high advance ?