vacuum advance

[rein]

I installed an electronic ignition in my Morris. The ignition takes care of mechanical and vacuum advance. When I program the mechanical advance in the software the engine runs fine. But when I start programming the vacuum advance there is too much advance and the engine starts stalling. When I check the advance with the timing light it corresponds with the setting in the electronic ignition.(Example: 1200 rpm 18 degrease btdc total advance)
The engine is an high compression engine so I use 14 degrease maximum vacuum advance. It made me wonder if the original vacuum actuator is lineair. The data in the Morris Minor manual states that the actuator starts advancing at 6 in HG. But it doesn' tell me if, from there it is lineair.
Does anyone know if there is more information available (on the net?).

Maybe I opened Pandora's box by installing this electronic ignition?

Cheers,

Rein

[bmcecosse]

Surprised it can deal with vacuum advance - but I imagine the original will be linear because it's just a fixed diameter diaphragm pulling against a simple spring. Note that vacuum advance is intended as an economy device to pull the timing forward when the engine is running on very light load - ie throttle almost closed/high revs = high vacuum in the manifold. When the throttle is opened for full power running - the vacuum drops and the vacuum advance drops off just leaving the mechanical advance - which for most A series engines needs to be about 30 btdc at 3500 rpm upwards - this obviously needs to be optimised for your engine, which you can do with your system! The original mechanical advance mechs were at full advance by 3500 engine revs (note that is 1750 dizzy revs) - and also note the original mechanical advance inside the dizzy has to be doubled - so if it was stamped '13' then that is 26 degrees engine advance - plus 4 degrees static initial advance = 30 degrees total.

[rein]

The electronic ignition uses a sensor. I connect the vacuum hose on to this sensor which translates the pressure (vacuum) in to a voltage. Works really well. (Although I need to back it down for the moment until I find out what is happening).
Tomorrow I will drive the car over the Rimutaka's. This hill climb will tell me if the Morrie is pinking. Actually, I hope that the engine will pink so I know I am at maximum advance. The display of this electronic ignition tells me the revs, the advance in degrease and the level of vacuum. I will only use this during testing and optimizing!

[bmcecosse]

Sounds great - Mini lads who fit 'Megajolt' mappable ignition report much improved flexibility and torque. Interested to hear how it all pans out - do you still have a dizzy - or is it completely electronic.

[rein]

It uses the dizzy but not the centrifugal advance. You can use different pick-ups (reluctor, opto, points) I used a reluctor from a car at the wreckers yard. It is a mappable ignition. If it works sattisfactory I will also include the optional knock sensor PCB. I allready fixed a sensor on to the engine. I only need to put together the electronics (assemble the ready made printed cirquit board). It is a project for the electronics hobbiest. I will let you know if I notice much improvement.

[rein]

I drove the Morris over the Rimutaka hills today. I noticed an improved throttle response, but only very small. First impression is absolutely positive. Although I use low octane petrol in this high compression engine it is not pinking (which surprises me a little bit), so I could advance the ignition even more. I won't for now, because I am happy with the power of the engine. Maybe later since it is only a matter of typing in some numbers! I still need to check the economy of the engine so I know if the vacuum advance needs adjusting. I am now the proud owner of a mappable ignition

[bmcecosse]

Yes - you should adjust the advance until it's 'just not quite pinking' - or - use the knock sensor if you can get it working. But in fact - with your ability to adjust the timing you may do better to use better grade petrol and adjust the timing to get the very best from it. many report that the increased economy more than offsets the slight extra cost.

[rein]

Do I understand correctly that the economy will increase when you are able to advance the ignition even more? This is the mechanical advance I assume because there is no vacuum advance under load and the engine is only pinking under load.
By the way, I noticed something that I never realised. When I close the throttle completly there is practicly no vacuum. When I gently open the throttle, the vacuum increases to maximum and decreases when I open the throttle further again. Is there a special reason why this is designed this way? When I look at the location of the vacuum connection on the SU carburettor this is what supposed to happen.

[bmcecosse]

You must have the vacuum connection in front of the throttle plate - far better to take a connection from the manifold directly - or from a spacer plate between carb and manifold - or anywhere AFTER the throttle plate. This way you will get genuine engine vacuum - and the appropriate advance for max economy during light running. basically - the mixture is so weak and so little compressed that it burns v slowly and so the spark needs to be ultra early to get it burning by the time piston falls over TDC. Under power conditions - the timing should be as close to the 'pinking' point as possible to get max power from the charge - economy is not a consideration under these conditions ! But effectively - max power will be = max efficiency and so max economy IF the mixture strength is correct of course. So your next project should be an O2 sensor (lambda) in the exhaust - and tune the mixture with that - which is exactly what fuel injection set up does.

[rein]

Thanks. I allready have an idea how to make another connection for the vacuum hose if I use one of those aluminium spacers between the carb and manifold. The vacuum connection on the SU is practicly on top of the butterfly. So that is why completely closed it is drawing no vacuum.
I have been thinking about a Lambda sensor. The electronics for it is not complicated. I only want to find out more on this subject (placing of the sensor, difference between O2 and CO2 tuning). But one thing at a time.
Plenty interesting stuff with this Morris Minor hobby.

[bmcecosse]

Indeed there is - especially if you also understand electronics. Any time I go near electronics it all ends in flames!