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MG Midget and Sprite Technical - Odd Tacho fault

1275 running an alternator conversion and Accuspark distributor...

Has been fine till today but firstly, the tacho needle started swinging wildly while accelerating. Now, when I turn on the ignition but before I start the engine the needle jumps to the 4000 mark. When I start the engine it stays up there and swings between 4 and 6000 regardless of the actual engine speed.

Thought it might have been a fault in the Accuspark so I disconnected that but the tacho still shows a reading of 4000 when I turn on the ignition.

The ignition light behaves normally i.e. comes on when I switch on then goes out when the car is running.

It's a very hot day. Nothing else has changed on the car.

Any thoughts?
graeme jackson

Have a look at Paul Hunt's site mgb-stuff for information or in the MGB threads as I think this subject has been covered there recently and with Paul contributing, if my memory serves correctly.

http://www.mgb-stuff.org.uk/hammertext.htm
Nigel Atkins

Well, after looking through some of the archives on here I moved the power to the accuspark from the coil to the fusebox (white connector) and the tacho started functioning perfectly, no wavering at all.
Took the car for quite a long trip today and she was running perfectly until I got to about 3 miles from home when the engine just cut out. Doesn't sound as if there's any attempt to fire so I suspect I've fallen foul of the well documented 'Accuspark distributors are crap' problem.
Looks like I'll be going back to the old points distributor until I can find a reliable replacement.
graeme jackson

Sounds odd Graeme, if you are running 1275 non-ballasted ignition there should be no need to run a wire to the fuse box. I can't find a 1275 wiring diagram but +ve coil should be +12v and therefore be OK.

Ballasted coils you need to run the wire to the fuse box for 12v, as the coil +ve is only 9v.

Are you actually suffering some sort of continuity problem to the coil?

In conclusion... actually, I don't know. And doubt the above helps! ha ha! Good luck with the fix. I have an accuspark in, but not had it long enough to talk about reliability, but hope it is good! :-S

Malcolm.
M Le Chevalier

I found the exact same symptoms in this thread...
http://www2.mg-cars.org.uk/cgi-bin/gen5?runprog=mgbbs&access=&mode=archiveth&subject=97&subjectar=97&thread=2009013014364025804

I'll take the accuspark to bits tomorrow night to see if anything has come loose.
graeme jackson

Quick update. Swapped the dizzy for the old points one and she fired up straightaway (thank the lord for making me mark the timing!). So, a simonbbc powerspark is now on order and I'll be carrying the old dizzy as a spare.
graeme jackson

This thread was discussed between 25/07/2014 and 28/07/2014

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