Tachometer

[Bigman]

I have a 1980 MGB. The tach reads right at low RPM but once you rev it over 2800 the reading goes to 5000 and higher. I replaced the tach with no help. Has anybody had a problem like this? Thanks

 

[Guest]

Mine is a '72 with the old points ignition. When I changed the ignition to a crane infra red pickup my tach started reading high but is not like you described. The instructions with my ignition recommended installing a capacitor to help this problem but I never did. At 55 mine reads 3600 RPM and about 3900 at 60 and 4200 at 65. I my memory serves me right, the capacitor was from the negative side of the coil to ground. Its been a long time so I'm not sure of the value.
A loose ground could possibly cause what you are talking about.
Bob

 

[Bigman]

Thanks for the reply. I tried adding a capacitor with no help. but I unhooked the alternator the tach read correct so I replaced the alternator with a new one still wrong reading now it's reading about double what it should. Thanks Curt

 

[Bigman]

I installed a ballast resistor between the positive and the power wire. I also replaced the power wires from the starter to the alternator with just one wire instead of two. Now the tachometer is reading correct. Curt

 

[Guest]

By the way, welcome to the forum since it looks like with 3 posts this is the first time you posted since signing up in Feb. Maybe you could post photos of your car in the member's rides area under links.
It would be interesting to see if the tach would read right now that the wireing is done by taking the ballast resistor back off. These were designed without a resistor and by adding it you would probably power your spark intensisty some. I'm not sure how much though.
Bob

[ 05-07-2004: Message edited by: mrbassman ]</p>