My new datsun (stock 74 120y sedan) runs rough and rich and needs a tune up. I've replaced points, condenser, dizzy cap and rotor.

I'm have a few issues setting dwell and timing. Probably has something to do with me not having much of a clue what im doing.

When I set the points gap to spec (.4 - .5), the dwell seems below spec like about 30

soory i didnt have time to read through every thing and try nutting thing out for you... heres a stie that may help
Setting points

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Thanks for the help guys. My meter was definitley set to 4 cylnder mode.

I wonder if anyone can answer the following question; If you change the timing does it effect dwell angle in any way?

(i really hope, and expect, the answer to be no)

i didnt know u could ajust the dwell angle any other way, other than points gap???? isnt dwell the time/angle the points are closed(coil is charging up, so to speak)??? timing is just at wat point/angle in the dizzy rotation the coil fires. i think that if u change timing it does not change dwell in any way. as u do not touch the points or cam lobe when changing timing. hope this helps mabey ur cam lobe thingy is worn????

Adjusting dwell will effect your timing. Adjusting timing will not effect your dwell.
Always adjust dwell/points gap before your timing.
I always found my 1200s ran best with advanced timing. I just advanced timing untill under driving load i could feel the engine was poor and detinating, then i simply backed of the timing untill the feel of the engine under load was good.

That advice is right.
Try to set the dwell at 49 degrees so that as the rubbing block wears, & the points open a little less, the dwell angle moves towards the other end of the permitted range [55 degrees]

The timing retards with use because the rubbing block wears over time & the distributor cam [linked to the crank remember] needs to turn a little further before it picks up the rubbing block & opens the points.
For all practical purposes, spark occurs at the moment that the points open, so if the cam needs to turn a little further to open the points, then the spark occurs later in the rotation of the crank. The timing is therefore retarded from the original setting.

I, & several others, have fitted a Pertronix electronic conversion to our 1200's & I for one am completely happy with it. The car ran better as soon as I reset the timing & as has been suggested, I too find that a few degrees more than the spec seems to be an improvement. The upside is that you never need to replace the points, adjust the dwell, or reset the timing again in normal use, ... ever.

I have now fitted a Bosch GT40R coil & I swear that it is noticeably better at highway speeds [85 to 95k in my stocker with auto] It's smoother & it needs less throttle at a given speed. Honest.
Well, at least it 'feels' that way.

also depends on how your dwell meter attaches.

If attached to a spark wire (spark lead), make sure it's on #1 and not on the coil wire. And that you are not using some fancy multi-spark system

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I'm still getting seemingly conflicting mearsurements of points gap and dwell, which makes me think (at least) one of my measurements must be wrong - I can't get my gap >0.4mm and dwell angle >49

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It seems to be running best at a large angle like 35