MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Tachometer

ALthough the engine in my '69 B is running smooth, the tachometer jumps around - (4-500) while idling and more when running at speed. Why? The speedometer does it a bit as well but not nearly as much as the tachometer. Has anyone run into the same problem? Thanks - Graham Dodd, Kamloops, BC
GA Dodd

I have the same problem with my speedo. Its fine while driving at 25mph. As soon as I put my foot on the acelerator and get up past 40mph my needle can bounch as much as 5mph, sometimes even more, so one never knows what speed I am actually doing... maybe I should wait for the cop with a speeding ticket to fnid my actual speed! :-)
GG Ginty

GA Dodd, Its most likely the guts inside the Tachometer are shot that might be why your tach is reading alittle off. It could also be the ground wire to the tachometer is lose or rusty check that wire connection. As for the speedometer Im on my third speedo and its highly possiable the inner working are shot as well. There are web sites to rebuild these gauges. I wish I could tell you how to rebuild them but Im not that advanced just yet.
James

The cable could be the speedometer problem. It may have a kink in the cable or it may need lubrication or re-routing. Go easy on the lube, too much can feed into the speedometer head.

Clifton
Clifton Gordon

im with clifton on speedo cable mine did same so replaced and it cured it
for tacho have you got electronic ignition as the pulses can cause this problem
ste
Ste Brown

I also experienced this issue with the tachometer. Check on the condition of your points in the distributor as this will affect the tacho in a big way. Good luck!
C Brennan

Problems with the points will usually affect running as well as the tach, in fact a jumping tach in conjunction with misfiring is the diagnostic for ignition LT problems rather than HT or fuel.

On a 69 the ignition feed runs via the tach, so problems here will affect running as well as the tach. From 73 the ignition was wired direct and the tach feed was a tapping off that, so problems in that tap would affect just the tach and not the running. However bad connections in the 12v (green) and ground (black) connections to the tach will affect the tach but not the running. If they are sound then the problem looks to be in the tach itself, see here http://www.classictiger.com/techtips/motach.html for the circuit and tips.
Paul Hunt 2

This thread was discussed between 09/05/2007 and 11/05/2007

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now