I've received permission from Hondaman to post his reply with the specifics about fixing the advance springs, so here ya go.
Well, the springs have never been a part, separate from a whole spark advancer. That's the BAD news.
The GOOD news is: yours are probably usable (with some mods) as it sounds like they are softened enough that at idle they are already advancing. When this happens, the points timing (even statically set) ends up being advanced by the slack in the springs, so when the engine revs up, it doesn't advance as far. This is pretty common on the earlier 750s before Hitachi (and then TEC later) got involved with making the advancers. While that didn't completely solve it, those newer versions pointed the way toward where the trouble was coming from: the springs were getting heat-annealed and lost much of their original strength.
What needs to happen first: cut off the loop on the end of one of the springs where it fits over the little post on the advancer's backplate. Then bend the next coil outward to take it's place. You probably won't be able to introduce the little 90-degree offset from the original spring shape, but that doesn't matter (it was actually part of the spring's design that CAUSED this problem...). Just bend the next loop outward to let it pop over that post again. Then, on the other end of the spring(s) where it hooks into the weight(s), 'shrink' the loop there because that loop has grown over time to introduce the slack that has become an invisible static 'advance' of timing about 4-5 degrees. The slack here is what makes the spark advancer appear to not reach full advance, because at idle the weights are already partially advanced, due to the slack here in both springs.
What these steps do is: it removes the slack that has accumulated in the now-stretched loops of the springs at the weights, and the shortened (by 1 loop) of one of the springs will slow down the advancer rate to bring it closer to full advancer nearer 2000 RPM again. Right now, chances are it reaches full advance (as far as the springs go) at about 1500 RPM, which causes fouled sparkplugs by firing too soon. This makes the engine spit back toward the carbs, which in turn slows down the airflow thru the intake tract, which makes the carbs act like the engine is running slower: the carbs mix richer at lower air speeds.
You'll also find that if you venture further, like removing 1/2 to 1 turn of spring from the 2nd spring, the engine will idle cooler and smoother and the throttle response, especially at low speeds in gear, will greatly improve. Our modern gasolines with ethanol in them burn very slowly: so slowly that today's Midgrades burn at the same speed as 1970s Premium did. The slow-burning fuel is made to light off catalytic convertors in vehicles. I've found that running Regular grade fuel in town and commuting works best without fouling plugs now, and I use Midgrade on the freeways and interstates unless I am carrying heavy (touring) weight, then I'll use Premium. The plugs stay cleaner and the engine runs much cooler with the lower octances. In the end I cut off 1 full turn from both weights and mine reaches full advance just before 3000 RPM now. It is MUCH happier, and lots smoother in city traffic.
And this reminder of places to find more info about your favorite machines: SOHC4.com and SOHC4.net forums
I'm delayed in getting my chop up because I finally stripped out one of the valve cover bolts that's been touch and go for a decade or two. I forget what they call those dodads to fix threads, but I'm sure I have a 6 mm one left.
Happy trails, all ya'll.
waj
