Rotor arm question - timing etc

I am troubleshooting some rough running on my Pop and I think I know what it is but I need it confirmed.

On my rotor arm there is no up or down play nor side to side but it is loose to twist through about 15 degrees before the springs provide any resistance and it doesn't return to the fully retarded position by itself. It doesn't have vacuum advance.

Am I right in thinking the springs should pull the rotor arm all the way back and hold it there? I think the rough running is because it's bouncing back and forth where there's nothing holding it back.

 

Sounds like a reasonable diagnosis--likely cure/tune is to start gathering small springs from later junkyard distributors, MrGasket and Moroso advance tuning kits or English equivaletnts, and go to work. Any spring that keeps curve under tension should cure the bad behavior if this is the problem, then you have to start hacking to get the curve fast enough for best acceleration.
I found that Moroso or such Ford and Mopar springs were about right size for Model B...
You can mark off total cetrif advance on rim of distributor, moving assembly by hand, then measure that with protractor. Then go to work with timing light and see if the thing is reaching full advance at reasonably low RPM, and experiment on road. At least a hatful of tiny springs is cheap speed equipment...
Check also on your rotor phasing, make sure rotor movement from zero to full advance keeps it reasonably near the terminal and not hunting between two of them...

 

Thanks Bruce, once again you've been a wealth of information!

I just stripped the dizzy on my lunch break and had a closer look. The two springs are closing the weights up just fine but it's the whole shaft turning about 5-10 degrees. That means it's either a bit of play in the two dog joints on the shaft or the gear is worn. I'm suspecting a bit of both so that's something I can't fix unfortunately. The only thing I can do is have a closer look when I fit the twin carbs because I'll get access to take the side cover off. I have a spare drive gear so lets hope it's a bit tighter...