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Ignition Timing


edwardatherton
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I have just put a 2.5 petrol into my 88" S1, and now have to set up/check the timing, fuel etc etc.

Anyway, the other day I twisted the dizzy until it was idling at it's highest, but it wouldn't rev up - it started coughing and spluttering. Nearly killing myself with the fumes in the garage I left it!

This morning I put the timing light on, and the timing was way too advanced at idle. I set it back to TDC and the revs dropped right back and it doesn't sound as happy...

I thought the idea was to get the highest revs at idle and let the dizzy do the rest?

BTW - I have still to set up the fuel (LPG then petrol) so that may be having an effect.

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timing is not set at maximum advance, it will pink and melt something, at idle with the vacuum advance disconnected is where you should set your timing, it should be something around 6 degrees before tdc. i'm not sure how many degrees but 6 is way close

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I have just put a 2.5 petrol into my 88" S1, and now have to set up/check the timing, fuel etc etc.

Anyway, the other day I twisted the dizzy until it was idling at it's highest, but it wouldn't rev up - it started coughing and spluttering. Nearly killing myself with the fumes in the garage I left it!

This morning I put the timing light on, and the timing was way too advanced at idle. I set it back to TDC and the revs dropped right back and it doesn't sound as happy...

I thought the idea was to get the highest revs at idle and let the dizzy do the rest?

BTW - I have still to set up the fuel (LPG then petrol) so that may be having an effect.

Factory static figure is TDC/0 degrees for 90 octane fuel.

Usually the engines run slightly better when between TDC and up to 6 degrees BTDC at idle with vac disconnected.

Dynamic test with strobe and vac disconnected should show

18-22 degrees BTDC @ 2000rpm

28-32 degrees BTDC @ 3000rpm

34-38 degrees BTDC @ 4000rpm

As Mark said - Don't set it up by ear.

If it is lumpy at idle on the right timing setting, then the cause is elswhere eg weak spark, poor ignition leads, weak coil, plugs gapped too wide, points not set correctly, poorly tuned carb idle mixture or leaking valves/badly adjusted.

Hope this helps,

Regards,

Diff

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Don't you have to advance the ignition a bit if you also run on gas? I think I heard somewhere that it's 3 deg.

Les.

Hi Les, you don't have to advance the ignition on gas, but it can help because LPG burns slower at low revs. The trouble is if you advance it too much, it will pink when running on petrol unless you have one of the 'dual curve' type ignition products.

Infact LPG likes a steep advance curve at low revs, but it levels off to require about the same amount of advance at high revs that petrol requires.

So, if you advance the static timing by twisting the distributor, you may well end up with too much advance at the top end.

This is noticeable with the 4 cyl landrover engines, because they have max centrifugal advance of around/near 40 degrees BTDC as standard and much higher than this will lead to engine damage at sustained high speed/load.

This is not helped by the fact that motorway work will require the engine to be revving hard.

It is interesting to note that it can be very hard to hear LPG pinking in these engines, even though pinking on petrol is readily audible.

One solution is to have the distributor 're curved' for LPG, but then it won't suit petrol operation.

A simple compromise is to keep the static timing under or up to 6 degrees, and this usually works ok on both fuels.

You can fit a programmable ignition system with two maps for best results.

Regards,

Diff

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  • 15 years later...
On 4/24/2007 at 9:11 AM, Tonk said:

timing is not set at maximum advance, it will pink and melt something, at idle with the vacuum advance disconnected is where you should set your timing, it should be something around 6 degrees before tdc. i'm not sure how many degrees but 6 is way close

Series 3 with 3 finger pointer on the engine....From the left to right as you stand  in front looking at the engine.......6 degrees before, 3 degrees before and TDC..............

set the mark on the crank pulley to the left market on the engine which is 6 degrees before TDC.

Hope this is of some help .

IMG_6482.JPG

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