Mine used to do the same thing,then one day it stopped working.I called a few places that specializes in car restorations,they gave me an idea what the problem was,but they couldn`t be sure until they tested it,and I was told depending on the problem it would be cheaper for me to buy a new one.After talking with these guys and getting some ball park figures and paying for shipping I think I`ll buy a new one,at least most places have a warranty with the new one.If you spent a lot of money in your old one and it coughs,then you are out that money and still have to buy one.NPD sells hood tachs for $259.00-269.00,part# C-9750-223B fits 69 Bird 8 cyl.5100 RPM redline.