I've noticed my tach needle has started to jump now.

Truck is a stock 86 F250, 460...everything is in my signature. What could be causing this?

 

IS it running smooth?
Mine was doing this too. but it started skipping and backfiring. The cause was the one-wire Dizzy semi "Sized"

 

Runs like a champ

 

Mine ran great and started to do that then it started to do it more well then I started having other problems, Well needless to say sparkplug wire #8 was bad and was causing a slight miss on #5 7 and 8 when I finally replaced the wires. Since I did this the needle has never jumped again on me and that was I think earlier this year.

So maybe check your plug wires, Mine was running great when it would do a blip jump on my tach but no change in the engine and power braking it did not result in a misfire under load. But it was a slight miss not noticeable but the tach was able to pick it up.

Just a heads up incase it is your problem just so you don't end up racking you brain on it for months and months like I did till the wire got bad enough to actually cause a noticeable miss.