Impending problem?

[wubie317]

My '77 Spider is actually running quite well lately. Over the last few days, though, I've noticed some 'missing' at steady RPMs so I think a tune-up is in my future. But what's more worrying is that at highway speeds, the tach has started jumping around. The needle falls a few hundred RPM without any noticeable surging of the engine...I don't feel any loss of power when it moves.

I'll soon do the points, plugs, etc. and I'll be sending a backup carb I acquired out to get rebuilt so I can hopefully get the choke working right (perhaps I've some plugged jets). I may have a head gasket leak, but compression has been good across all cylinders.

Any thoughts on whether there's something big going on?

[baltobernie]

Next time the tach starts jumping around, wiggle the ignition key and see if it fixes the problem.

[wubie317]

Next time the tach starts jumping around, wiggle the ignition key and see if it fixes the problem.

In which case, I may have a dying ignition switch?

[bradartigue]

open the distributor and spray it all out with electrical cleaner. if your points are old and nasty they just might have accumulated enough dust to trick the tach. Then, regardless of outcome, I'd do the tune-up and then worry about the tach.