There should normally be 2 springs- they are usually of different "strengths" to extend the range of the ignition advance so you have probably lost one. This would probably result in too much initial ignition advance but this could be compensated by retarding the initial static setting by rotating the distributer result = poorly performing engine but with a big V8 you might not notice?
This is a good explanation from a Triumph "Dolly Sprint" article
HOW TO CORRECT POOR IGNITION TIMING.
Maybe you've just built up a brand new engine, or upgraded the cylinder head and changed the camshaft, perhaps you're simply trying to improve the running of your stock standard engine on ULP or PULP. In any of these scenarios, one area of tuning that is highly overlooked and greatly misunderstood is timing. All too often, people drop in their distributor, making a quick adjustment with their timing light, and set off thinking that all is well.
Timing is everything, and without a proper timing curve, every thing else goes out the window. Jetting changes, and other adjustments, are all useless, if first the timing is not set correctly.
There are numerous articles available, that go through the how and why information about ignition timing. What will be explained here, are some basic problems that can be encountered with mechanical distributors.
The basic mechanical distributor has 2 functions relating to ignition timing. The first function is the rate of ignition advance, (advance curve) and the second function is the amount of total ignition advance available.
The advance curve is controlled by the springs attached to the bob weights within the distributor. Most distributors have 2 springs, one light spring and another stronger spring. The relationship between these springs calibrated the speed that the bob weights move and therefore the advance curve. If the springs are too soft, the ignition advances to fast, which will cause pinging at relatively low rpm. If the springs are to hard the motor won’t perform to its optimum, due to lack of ignition advance for the given RPM.
The bob weights control the amount of maximum ignition advance that is available from any given distributor. Usually stamped on the weights will be numbers like 8,10,12, etc. This is the amount of advance that is available form this particular distributor. (Remember that 10 distributor degrees = 20 crankshaft degrees). If you have to much total ignition timing the motor will ping at high RPM, ie the distributor is a full advance, and if you do not have enough ignition advance, the motor will lack performance and usually return poor fuel economy.
The total ignition advance varies from engine to engine. You can identify what your motor is currently running at, by adding the static timing figure to the total advance taken from the bob weight. 10 static + (10 distributor x 2) = 30 total.
Most motors are at full advance by about 3000 RPM, so as stated earlier if the motor pings below full advance, more than likely the springs are soft.
The easiest fix for pinging is to retard the ignition timing. If the problem is right through the RPM range, (high RPM pinging under full load can be hard to detect), retard the distributor timing, but if it pings in the low/mid range RPM, retarding the distributor can have major effect on the performance of the motor at high RPM.
