Unleaded Timing Adjustment

Post by **pentane66** » Mon Mar 13, 2006 5:15 pm

Hi all, Fistly let me admit i am a young in-experienced 1967 Minor 1000 owner. This is my first car and i love to be able to lift up the bonnet and know what is going on - anyway onto my problem. I have had the head replaced so that the car can run on unleaded petrol. Unfortunatly i cannot get the timing quite right now. Does anyone know the correct timing adjustment for an unleaded conversion. I am using standard 95ron unleaded petrol.

Post by **Willie** » Mon Mar 13, 2006 6:08 pm

When you say you cannot get the timing right what causes you to say that?
On all Minors you should set the timing so that you just get pinking (a light
metallic tinkling sound) if you try to accelerate up a SLIGHT slope with the
engine at normal temperature in top gear. Once you reach this condition then
retard the timing slightly. Six clicks on the A/R adjustment wheel on the dizzy should do it.

Post by **bmcecosse** » Mon Mar 13, 2006 8:34 pm

That's it - advance till it pinks - then back off very slightly. The actual static timing matters very little - as long as it doesn't 'kick' against the starter. Worth while checking that the vacuum advance still works (suck the pipe and watch the base plate in the dizzy move) and that the centrifugal advance is still working - twist the rotor arm against the springs and make sure it comes back ok.

Post by **pentane66** » Tue Mar 14, 2006 8:29 am

Vacuum advance works well (recently replaced as the old one had a lovely hole in it) I will try your recomendations.

Cheers

Nick

Post by **bmcecosse** » Tue Mar 14, 2006 10:02 am

Well done - they don't last much beyond ten years. Not inexpensive to replace!

Post by **KirstMin** » Tue Mar 14, 2006 12:06 pm

bmcecosse wrote:Not inexpensive to replace!

Or ditch it and seal the SU where it come in. Saves replacing it.

Post by **Onne** » Tue Mar 14, 2006 4:29 pm

ditch the vacuum advance?

Post by **pentane66** » Tue Mar 14, 2006 5:03 pm

KirstMin wrote: Or ditch it and seal the SU where it come in. Saves replacing it.

I was not aware this was possible, Surely this must affect performance when driving.

Post by **Cam** » Tue Mar 14, 2006 5:35 pm

No, but it affects economy. The vacuum advance only comes in at partial throttle. When you floor it there is no advance from the vacuum unit as there is no vacuum.

Post by **bigginger** » Tue Mar 14, 2006 5:35 pm

bmcecosse wrote:Well done - they don't last much beyond ten years. Not inexpensive to replace!

Not inexpensive? So 'expensive' then?

Post by **bmcecosse** » Tue Mar 14, 2006 7:12 pm

Not cheap either ! It is an economy device - and these days we need all the economy we can get. I find it also makes the engine a little 'sharper' - when I put foot down the advance is still there for a second or so (until the vacuum collapses) - I hear a slight tinkle just for that second and the car seems to accelerate away rather better. All this compared to the older dizzy which had a knackered vacuum unit. I think new vacuum units are about £ 30 - sometimes see them on ebay for much less. Have to wonder how much longer they will be available since not used on any modern cars.

Post by **bigginger** » Tue Mar 14, 2006 7:20 pm

Fair enough - a genuine question, BTW

Post by **KirstMin** » Wed Mar 15, 2006 6:46 pm

bmcecosse wrote:I find it also makes the engine a little 'sharper' - when I put foot down the advance is still there for a second or so (until the vacuum collapses)

erm... you'll get better power output without the advance unit. Thats why they take them off and plug em up when race tuning. I dont find any lack of sharpness without one. I don't s'pose many of the mini men do either, it's a pretty common thing to do.

I think the stats are approx 1/2 - 1 mpg increase in efficiency with a vacume advance on. Not a lot but to BMC, that's might be enough

Post by **minor_hickup** » Wed Mar 15, 2006 7:37 pm

I thought when tuning on a rolling road or dyno they altered the advance curve to suit the engine?

Post by **bmcecosse** » Wed Mar 15, 2006 7:46 pm

Very few people do without the vacuum unit these days Kirst! It was taken off the Cooper S dizzy to prevent over-advance - but it can no way 'increase' the power to NOT have a vacuum advance unit. It only takes effect when there is substantial vacuum in the inlet system - ie when the throttle(s) are closed/only slightly open. I relate my own findings with my vac unit - others may of course have different views. Much discussed on minifinity - general view there now is to convert to completely electronic systems (megajolt) which have no dizzy - but do still take a signal from the vacuum in the inlet manifold. If i could afford it - i would do it. The timing can be mapped up with a lap-top to give precisely correct timing under all engine conditions.

Post by **KirstMin** » Thu Mar 16, 2006 3:19 pm

Aye, point taken (about power gain) but it appears particularly effective when you drive with a heavy foot. I was told there are plenty of non electronic set-ups without vacume advance. At least that's what they said when mine was removed at the rolling road!

With regards to minor_hickup's point; I was under the impression that you could only map the advance curve with the electronic set-up (as described above) and most of us dont have these!

Post by **rayofleamington** » Thu Mar 16, 2006 3:32 pm

Having driven Wilberforce with the Vac advance plugged and then reconnected (new pipe) I have to say I couldn't tell the difference, but i'm (for once) in agreement with bmcecosse - every drop of petrol counts at todays prices!
At only 1mpg difference, a £30 vaccum advance unit would pay for itself in ~10,000 miles.

Post by **KirstMin** » Thu Mar 16, 2006 3:59 pm

rayofleamington wrote:but i'm (for once) in agreement with bmcecosse

Don't agree with him. He'll get a big swolen head and then god knows what will happen

.

Tell you what though, the amount of miles I do i wouldn't make me money back in 5 years!

Post by **minor_hickup** » Thu Mar 16, 2006 7:41 pm

KirstMin, i believe its done by drawing the necassary advance curve and modifying the distributor's weights and spring tensions to try and match it.

Post by **bmcecosse** » Thu Mar 16, 2006 8:11 pm

Arghhh - head swelling by the minute! TBH - I couldn't care less if you agree with me or not - I KNOW I'm right!!!

Do you like that ??

The mechanical dizzy can be 'mapped' by adjusting the bob weights and the springs - and sawing the end off the little stop to give more total advance - but how on earth to get the best results without a rolling road? The megajolt allows mapping from a lap-top, so I gather the method is to drive along at different speeds and loads (mainly up hills!) and a friendly computer expert in the passenger seat adjusts the 'mapping' to get the best (ie not quite pinking) settings under various conditions - and the saves the settings into the unit. However - as far as I know it doesn't have a 'knock' sensor, as modern engines do - and so it just works with the settings you give it and cannot compensate for different petrol grades etc. Peeps who use it (on Minis) say it is excellent.

BTW - just kidding about the swelling head.