Some MG tachometers have an adjusting screw on the back side of the case, I'm
not sure if your 1973 has this feature. This screw will allow you to make small
adjustments. Of course you will have to have a "known" rpm to calibrate too.
Larry
>-----Original Message-----
>I have checked the tachometer in my 73 B GT (RVC2415/00) against my
>digital car multimeter and a brand new instrument from another maker and
>my suspicions were right:
>a. it shows about 500 rpm more at idle (engine turns at 750, tacho shows
>1,300)
>b. it won't register more than 3,700 - 4,000.
>
>Having examined the electrical diagrams in my Haynes I've noticed that
>some cars have a "loop" on their tachos, not part of the diagram for my
>car though. Then again there are some errors in those diagrams (e.g. the
>distributor is numbered/called a "lighting switch" in the 73/74 diagrams
>on page 194 and there is no entry for switch #36 in the key on page
>193). Should my car have such a loop (it doesn't now) and could this be
>the cause of the problem or am I to look for a replacement tacho?
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