put on dry, Ive never had a problem and tune up 200+ boats a year

Since when does the rotor control the timing of the engine? That is the job of the points, or magnetic pickup, or crank trigger, whatever type of triggering system your particular engine has. The position of the rotor determines phasing, not timing. Phasing refers to the position of the rotor in relation to the plug terminal inside the cap at the moment the coil discharges.

I replaced the stock Delco cap and rotor on my HP500EFI with parts from MSD.

Larry

62 Bel-Air 409

260 Eagle XP HP500EFI

2002 Corvette M-6 Coupe

Since the pickup trigger is attached to the rotor. If it is allowed to move in relation to the distributor shaft, the timing moves around too. See it all the time. Not on new parts but on used.

timing is described as the timming of the spark in relation to the position on the piston


the relationship or position of the rotor to the dist cap IS what controls the timing or when a particular cycliner is fired in relation to the piston position, the trigger or points control the length and when a spark is fired in essence all control timming

So following your line of thinking, how does the timing change from inital to full advance? The rotor mounts to the top of the distributor shaft, which drives off the cam, which is driven by the crank. All a mechanical link. The rotor and timing ARE independent of each other.

You can't have it both ways. Either the rotor controls timing or the trigger mechcanisim controls timing. And believe me, it aint the rotor, just sends spark to the approiate terminal, the trigger determines when. Haven't seen a distributor yet that can contol the length of a spark, an MSD box can extend the duration up to about 3000 rpm. Suggest you go to the MSD site, and read the article regarding rotor phasing, perhaps this will help you to understand what is going on inside the distributor.

Maybe you are to young to remember points in a distributor. you could adjust the length of time the points stayed open (dwell) there by adjusting the length of the spark.
If the rotor is loose on the distributor shaft, it could act just like a mechanical advance without the springs.That is why the timing would be irratic.

The rotor on a mechanical advance distributor moves with the advance trigger wheel or cam so as to not affect rotor phasing. It does not have any real effect on ignition timing. The total time for a spark to jump the gap between the rotor and the dist. cap is measured in milliseconds. having the rotor move back or forward slightly from it's indexed position will not affect timing by any more than a few milliseconds but will have a large effect on secondary firing voltage.( "firing voltage" ) Having the rotor phased too late or early can cause crossfires between cylinders but it has to be a long way out of position for that to happen.
Dwell adjustment changes the charging time of the ignition coil, not the "lenght of the spark" actually called "burn time". Too short of a dwell time will undercharge the coil and cause a low firing voltage and short burn time if any but too long of a dwell will not cause a longer burn time than the combustion pressure,fuel mixture, rotor to cap gap and spark plug gap and total secondary resistance will require to form the arc.

You have obviously never worked with a Merc T-4 ignition. The trigger and rotor are together. The box controls the advance. If the trigger moves around if relation to the dist. shaft, the timing moves around too. If you dont believe me. I have a bunch of old rotors you can put on a t-4 and watch the timing marks on the balancer jump around.