The tach on my '73 engine is acting strange. After several minutes of smooth running the tack all of a sudden will start to fluctuate between the current RMP and zero. It always seems to run fine for a couple of minutes, then goes hay-wire. It's not the gauge, the same thing happens on an old tach/dell meter. I've installed an MSD system with the tach adapter. I needed to do this when I switched chassis and the old CDI system went away with the old chassis and the CDI with the new chassis was incompatible with the '73 motor. I've swapped coils three times and still have the problem. Interestingly, there is no apparent change in engine sound or audible performance change. Any help in pointing me in the right direction would be appreciated. Thanks, Rich Lorenz

 

I know my tach used to act wonky when my points got out of adjustment. It was the first signal that i needed to adjust them. Then i went to a Pertronix unit and solved that issue.

 

I had a similar problem and I just had the points replaced
and I just picked the car up today, so far no problem.

Also you mignt want to check for fualty grounds, the can
cause all sorts of nightmares.

Regard,
Rich

 

I'll go with a bad ground. Replacing the straps is one good cure-all for 911 ailments.

 

Thanks for all the responses. I think I'll check the ground straps. This motor was just put in the car and hasn't been driven much at all. The points probably need to be checked also. The strange thing is the motor doesn't seem to be affected with regard to performance.

 

Yes, it's funny, the tach seems to get jumpy before you notice the engine...but sooner or later you will, if you let it go.