advance and retard
Discussion
You disconnect the vacuum when setting the timing otherwise the engine will be adding advance due to the vacuum created and there's no way of knowing exactly how much this would be, so its far more repeatable for the manufacturers to quote ignition advance at idle with no vacuum.
As mentioned check the TDC mark by fishing out no.1 plug and having a feel with a wire probe while your glamourous assistant turns the engine by hand.
Also well worth doing anything you can to reduce the heat picked up by the intake; wrap manifolds, insulation around inlet pipe, isolator plate, smaller no. plate , de-cat etc etc
Hot air encourages pre-ignition
Matt
As mentioned check the TDC mark by fishing out no.1 plug and having a feel with a wire probe while your glamourous assistant turns the engine by hand.
Also well worth doing anything you can to reduce the heat picked up by the intake; wrap manifolds, insulation around inlet pipe, isolator plate, smaller no. plate , de-cat etc etc
Hot air encourages pre-ignition
Matt
just been set up by a well known company they made the car run alot better, but just curious about why it was disconected .the other problem is the car guzzles petrol.i would say about ten to a gallon .went from mapperley from where i live to just past bingham to a local tvr car meet .twenty quid had been used up .can`t aford to drive this car any more thanks
just been on the net and found some cams advance the ignition on tick over and part throttle causing the pinking , may be this is why my car had the vacume advance disconected but as a result the car as lost that bite from the start and uses alot more fuel ,may be the timming as been set a little advaced to allow for the vacume not being connected .
Getting the vacuum advance right is more difficult, the standard vacuum units have no scope for adjustment although after-market units are available with it. The vacuum advance is intended to compensate for varying load and throttle openings which will affect the density of the mixture and does the job reasonably well, but cannot correct itself for camshafts which alter the vacuum at idle and low speed and small throttle openings. It does nothing when the throttle is more than about a 3rd open on most engines and can apply adjustments of up to around 8 degrees usually. Since most performance and large engines still end up spending most of their time at idle and very low rpm with small amounts of throttle, this is a sensitive area and can effect tractability and economy quite noticeably.
It's impossible to get the ideal timing with the distributor even using a rolling road, but careful experimentation can achieve reasonable results. Short of using a fully mapped electronic system like GEMS or MOTEC there isn't really much that can be done although there are programmable systems available from MSD and Mallory which can replace the inertial advance mechanism for racing use. For LPG there are ignition amplifiers available from Iwema, RPI and others which can advance or retard the timing by a set amount to compensate for the slower flame propagation of LPG. These can be particularly useful on high compression engines where LPG can run substantially more advance than petrol.
It's impossible to get the ideal timing with the distributor even using a rolling road, but careful experimentation can achieve reasonable results. Short of using a fully mapped electronic system like GEMS or MOTEC there isn't really much that can be done although there are programmable systems available from MSD and Mallory which can replace the inertial advance mechanism for racing use. For LPG there are ignition amplifiers available from Iwema, RPI and others which can advance or retard the timing by a set amount to compensate for the slower flame propagation of LPG. These can be particularly useful on high compression engines where LPG can run substantially more advance than petrol.
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