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MG Midget and Sprite Technical - 1500 dynamic timing vacuum on or off

checking timing do you do it as per mg manual with vacuum advance connected or as per hayens with it dissconnected ?
mark 1500 Lights on at the end of the tunnel

Hi Mark,
I would do it with the vacuum disconnected but I have a 1275 (and 123 tune which was set up by Peter Burgess on his rolling road). That way you are not getting the vacuum bit of the timing giving you incorrect figures.
In fact I would recommend a 123 tune and rolling road setup. Peter is just down the road from you, give him a call...

Dave

PS I have no connection with Peter apart from satisfied customer.
Dave Brown

I've always understood that timing is checked with the vacuum disconnected but sealed off at the carb end. That way, as Dave says, you are just checking the mechanical setting.
One issue that I realise has given me problems is over the use of electronic ignition. With Simonbbc (and others?) the static timing light across the points doesn't work so "static" needs to be set with the engine running and use of a strobe. Be aware that your mechanical advance may be intended to come in very early so if your tickover is a little too fast, you may not be getting a true static setting because the mechanical weights have added some advance!
Graeme W

did it both ways and not much difference so must depend on how fast tickover you have set mine about 850rpm.
mark 1500 Lights on at the end of the tunnel

Or maybe your vac advance isn't working.
Dave O'Neill 2

Mark - was that both ways meaning "with static light" and with strobe
- or with and without vacuum?
Graeme W

Have a look at this:
http://mgaguru.com/mgtech/ignition/pdf/lucas_distributor_specs.pdf

My first reaction when I saw this a while back was "bl**dy hell, HOW MANY distributors are there!"

Your dizzy might be 41646. Look how early the mechanical advance comes in! At 750 rpm you have an additional 3 deg over the static.
Graeme W


with and without vacuum slight difference seems to advance ok when revved but slight miss when running on road seemed to get better after a while
mark 1500 Lights on at the end of the tunnel

Quick queery regarding ignition timing as my dizzy is a 45d4 41449 and timing according to manual should be 10 degree btdc at 680rpm, i assume that takes into account that at 700rpm mech advace is 4 degrees and at 500 mech advance is 2 degree, so if i am setting timing at around 950 to 1000 rpm and mech advance is 5 degrees, should i add an extra 1 to 2 degree so around 12 btdc dose this sound about right , and could this be why i have a sligt miss fire.
mark 1500 Lights on at the end of the tunnel

This thread was discussed between 05/06/2014 and 07/06/2014

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