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MG Midget and Sprite Technical - electric tach jumpy

This question applies to 1968 Sprite with electronic tachometer. it jumps wildly (full scale) until the about 4500 rpm. It is generally ok at idle. It was doing the same thing 2 years ago and we had the tachometer rebuilt and tested by Nisonger. It never quite worked right when we got it back but we did not get around to tracking the problem down. It had spells of working and then finally started jumping wildly again. Nisonger sent instructions to bypass a lot of original connections since they have seen the problem in connections before. As I recall the directions were to run a wire direct from the distributor to the tach.
Does the problem sound familiar or common?
Brett
bew wright

This condition seems to be worse in high ambient temperature situations. I recommend sending it to MOMA in Albuquerque for repair. Typically it is semi-conductor failure.
Glenn Mallory

Yes...

but i lack enough knowledge to really explain it all

it depends alot on the type of elignition system you have ... is it orginal or is it modified

the best way is to go back orginal then add in the componets and work your way in that direction

to help us...it maybe best to list all your ignition components wnd modifications and your type tach ... the coil the dissy is it points and conden or electronic and what kind of electronic... the whole 9 yards

probably the best person here to talk with is trevor jessie ... but id put several others on this short list.. but i only have 2 hours before bed....haha

post this question on the (MG experiance website also) they got a few egg heads over there as well) good luck its going to be an adventure ..

a 1098... was it pos or neg ground ?

Prop
prop

Brett, a flickering tach needle is usually an indication of a L T circuit fault and often accpanied by a misfire. So its not necessarily the tach itself, though it could be.

Check all the other components on the L T side. Coil, points gap, condenser, ignition switch. Also check your distributor shaft for wear that could be throwing the points settings out.
GuyW

My tachometer occasionally had a 'fit'. It would work correctly and then the needle with no forewarning would dart all over the gauge and then fall to zero and once seemingly rested carry on as if nothing had happened.
The fault was a bad solder connection on an in line fuse.
Alan
Alan Anstead

Mine used to do that. I thought it was a bad connection somewhere and I had the whole thing apart. However, once I swapped back to copper ignition cables from silicon ones the problem touch wood seems to have disappeared.
Matt1275

The electrical side of this 1968 sprite is rather original, Points and condenser, recent rebuilt stock distributor, all wiring everywhere is original. Car runs strong and does not having symptoms of missing or misfire. It could be a bad tach again, but remember it was recently repaired and really never operated perfectly after that. Makes me think there is a gremlin connection issue. The tach is the type that has the little induction loop on the back.
BEW Brett Wright

Sorry Bew

i read your post to mean your gauge was an aftermarket and you had a modified ignition system

along with the other above issues ... id add in a double gounding situation these wires over time get brittle and loose insultaion of start chaffing on sharp edges... eventually catch fire

what i would do is find another british car thats working fine ... spridget mgb austin mini spitfire ect ect that has a similar ignition system and hook your tack into there car for a test to make sure your tach is working as should be... or send it off to have it tested... but take that part of the equation 1st ... make sure your tack is working 1st ... once thsts varified then work the rest of the problem

as pointed out... at this point it could be anything ... from cooper wires to odd plugs to a bad soilder inside the the tach

we need to know for a fact that the tach is good 1st before all else... or its just a guessing game centered around a dart board tounament for blind people

prop
prop

This thread was discussed on 09/05/2016

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