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MG MGB Technical - Accuspark

I have recently fit and accuspark unit to my MGB in place of the c.b. points, and I am suddenly aware that the engine is not switching of immediatly when I turn the ignition of and tends to run on for two or three seconds and then stops, This is not pre ignition as the engine is smoothly ticking over when this happens.
This Accuspark technology is based on the hall effect, the question Im asking myself is there any capcitance build up in the rev counter and is it discharging through the coil and Accuspark unit and causing the engine to run on. Your comments would muc be appricated.

Regards Patrick Tighe
P.T. Tighe

Did you set the timing with a strobe after fitting the accuspark?
Allan Reeling

Hi Patrick,

None of the different tachos have any energy storing devices that could "run" the ignition. As Alan suggests, check your timing, run on is common in Bs.

Herb Adler

Hi Herb Hi Allan,

Thanks for your input, timing set at 15 degrees 600 revs with strobe, car runs good no pinging befor this started I did note on two occasions that that when the engine was switched of it stopped instantly the rev counter droped to zero and bounced backup to 4000 revs.

Regards Patrick Tighe
P.T. Tighe


When this happens do you have the heater blower switched on by any chance?

I have a totally different engine (a Rover 3.9 fuel injected V8 with electronic ignition) in my B with exactly the same problem the engine continues to run for a second or two after switch off but only if the heater blower is on. I wonder if there is sufficient inertia in the blower motor to act as a generator?

Geoff King

Hi Geof,

Ive never noticed if I had the heater on but I will check it out.

P.T. Tighe

15 degrees is a bit too advanced on today's fuel, unless you are using octane booster. you might not notice pinking at lower speeds, but I bet you are getting high speed pinking, and that will be heating things up in the combustion chamber. If it is you will notice the temp rise a bit. Re-time to 12deg, vacuum disconnected. A few things can upset hall effect. Un-surpressed leads, non-resister plugs, cracked dizzy cap, you might also have a sticking switch contact.
Allan Reeling

Hi Allan,

I wil take your advice and give it ago, I will reset the timing to 12 deg and let you know the outcome,I always run my car on 97 octane fuel as it pinks when on 95 oct its also a high compression engine and has been bored out to 1995 cc, still I will reset the timig.

Regards Patrick
P.T. Tighe

This thread was discussed between 14/04/2012 and 16/04/2012

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