dancing tach & rough idle

[beachking07]

my tach seems to be jumping with the engine idle. also from idle to 2500 rpm the engine almost sounds as if its miss firing, and runs really rough. after 2500 it sounds great and smooth. are these problems related? any help would be great...specs as follows.
MSD-83606 distributer, blaster II coil, 72 chev 400 SB. merc alpha1 drive.

[SmokinLowriderSS]

Check all the ground connections, then check-em again. No paint, rust, anything between the connections. Then make sure tach wire isn't chafed on something somewhere (all coil feed wires actually).

[Squirtin Thunder]

my tach seems to be jumping with the engine idle. also from idle to 2500 rpm the engine almost sounds as if its miss firing, and runs really rough. after 2500 it sounds great and smooth. are these problems related? any help would be great...specs as follows.
MSD-83606 distributer, blaster II coil, 72 chev 400 SB. merc alpha1 drive.
First off is this old tune-up parts and new problem or new parts on an old problem ???

[sanger rat]

Make sure the distributer wires are not any where near the coil wires.

[Moneypitt]

If you feel your problem is related to the tach, disconect it. Remove the tach lead from the negitive side of the coil and see if the motor still stumbles. If it does your tach is not the problem but is showing you a problem in the ignition system. Re attach the tach lead and look elsewhere for the stumble..........MP

[progplb]

Check all the ground connections, then check-em again. No paint, rust, anything between the connections. Then make sure tach wire isn't chafed on something somewhere (all coil feed wires actually).
Yes! Boats and bad grounds seem to go hand in hand.. Make sure that you have a good ground going forward to the dash components could be Tach problem. But I doubt it would make it miss.

[beachking07]

this is a new problem on new parts. new rebuild, new ignition. I havnt checked the grounds yet. there not close to the coil leads though. i will also try taking the tach out. thanks guys...

[SmokinLowriderSS]

One of the things I do to fight ground problems (corrosion problems really) is go to a hardware/lumberyard/home center, whatever store, wander the electrical isle(s) and find a substance called "Nokorode Paste". It is intended to prevent aluminum wire from corroding in a connection to copper wire (I used to ba a maint tech in apartments). It works great on batteries and all other elec connections I have tried. I would stick with Di-electric on spark-plug wires, but I use a small tube of Nokorode on just about everything else. Is usually found in a white & red tube, small and large, greenish paste (olive drab really), and a little goes a long ways (kinda like Brylcream). :cool: