Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
The tach itself bouncing will have no effect on your ignition timing at all. From the sound of it, the problem is most likely gonna be the tach itself. If you have a reversable drill, you could spin the tach cable with it, and see if the noise is still there, and the needle still jumps. If it does, then your issue is with the tach. If it does not, you prolly need to remove the tach driven gear from the distributor and have a look-see. The fitting on the dist where the cable connects is screwed in, and can be removed. IF the gear there is damaged, chances are high that the dist shaft itself is also damaged...
____________________________________ Joel Adams C3VR Lifetime Member #56 My Link
Vette(s): 1978 Silver Anniversary L82
Previously: 1965 300hp Coupe in 1967.
1967 435hp Coupe in 1968-70.
1969 350hp T-top w/ac and all power options.
I had the same prb in my 69 350, only 15K miles on it and the tach dropped to 0. Replaced the stripped tach gear and it started working, but jumping and then it quit again. It turned out to be the distributor shaft having a broken tooth, so rather than replace the dist I added an electronic tach on the steering column. Then you can set your own redline!
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