how do you set the dwell?
Points gap should be set beteen 0,3 and 0,4 mm (0.012-0.016). You can use a feeler gauge.
Or you can use a dwellmeter that registrates the degrees the crank rotates while the breaker points remain closed. So, the higher the dwellmeter reading, the smaller the point gap. The shorter the dwell, the wider the point gap. I prefer the meter. Some DMMs have this function. It's easier, more precise and you're able to check for irregularities at different rpms. On 500/550s breaker point dwell should be in between 98
0-92
0 or 49
0-46
0. This depends on what scale your meter reads. If you're lucky enough to have a dwellmeter that reads american style, it's even easier as they registrate in %. 98
0-92
0 or 49
0-46
0 translates in 54,4-51,1%.
Setting the dwell should precede the timing. Once you have set the timing correctly, you can - later on - correct the timing, if necessary, by simply bringing the contact breakers to their correct dwell again and you don't have to bother to loosen the plates anymore. Less screws to work on.
For those of you that prefer, like me, the dynamic procedure and use a dwellmeter, here is a tip.
Years ago I have attached two ‘blind’ extra wires on my coils (12V-) both with a female connector at their end. Once you have set your timing correctly, these wires allow quick diagnoses later on. Write down the dwell for future reference. Almost all changes in timing originate at the contactbreakers. When the dwell changes, so does the timing. When you suspect the timing is off, simply connect the dwellmeter to the extra lead 1&4 or 2&3 and you can verify if dwellangle is still the same or has changed. It’s important that those female connectors are well shielded to avoid groundcontact.
I have had these wires attached for years now. What I like is that I can check really quick without even to remove the ignitioncover.