michaelb wrote:
Running on is pre ignition which is caused by ignition timing too advanced or compression is high and fuel is not high enough octane, 98?
First, I would get a good tune up
How can running on be caused by ignition timing being to far advanced?
The ignition is switched off when the engine runs on so does not come into play!
Running on in the Majority or cases is caused by too much Air and Fuel at Idle.
There is too much air and fuel simply because the Butterfly has to be, relatively, a long way open to allow the engine to Idle at an acceptable speed.
There for it is supplying Air and Fuel to the engine which allows it to run on.
So How do we stop the engine Dead when we turn off the ignition, Simple!!!
We have to turn off the Air and Fuel as well.
Late model Japanese cars With Carburettors ALL used this method/
They had a fuel shut off solenoid fitted to the idle circuit on the carburettor as well as a solenoid which allowed the butterfly to close completely.
I understand that some later model cars fitted with SU's used this butterfly solenoid as well to shut off the Air. With an SU no air no Fuel so kills 2 birds with one stone.
Anyway Back to the Old fashioned Mini Engine.
The reason Most Mini engines have to Idle with such wide open butterflys is simple/
It All comes back to the Lucas Distributor with its Advance Curve.
Most Mini Lucas Distributors have 15degrees of Mechanical Advance which equates to 30 degrees at the Crank,
The total Advance for the Average Mini Engine should be Around the 30 to 32 degree mark.
So with the standard mini Distributor you are stuck with an initial Timing setting of 2 degrees BTDC to give a total advance of 32 degrees.
Now, to get an Idle with only 2 degrees of initial advance requires the butterfly to be relatively a long way open. This creates a condition of excess fuel and air which causes the engine to run on when the ignition is switched off .
On the other hand if the Initial is set to 10 degrees BTDC the idle speed Speeds up Very Considerably which allows the engine to Idle Smoothly with the butterfly closed down to the almost fully closed position.
No More Running On...
But with a standard Distributor 40 degrees of total advance is way too much.
The Distributor must be modified Mechanically so it has no more than 11 degrees of mechanical Advance and then the curve has to be set up for your particular engine.
So 10 initial, and 11 in the distributor which equates to a total of 32 degrees
Obviously these figures will not suit all engines but one thing is for sure,
Run as much Initial advance as practical and Keep those Butterflys Closed................
Dave