Part #30220-300-154 The original on the left vs aftermarket one is obviously bigger. I'm assuming they are interchangeable and the advance rate, weights and springs are calculated for early 300 manufactured bikes ‘69-‘72. Says 300 on it. I got the part from 4into1 and the photo from DSS looks to be the same as the 4into1 part. Has anyone had a problems with the aftermarket ones being different size than the one on my K1?
I recommend using your old springs on these 4into1 advancers. I've worked with several of them, and their spring rates have been different on each one(!). When you install your springs, make sure, at the very least, that all the 'slack' is removed from your springs to fully pull the cam to 0 advance at idle speeds.
Most of the time, the old advancers are fine unless the springs have become too heat-softened. This happens to 100% of these units now, as they were originally intended for a 6- to 10- year lifespan (as were these bikes!). At the very least I will re-curl the outer ends of the springs to take up the 'slack' and put more tension on the points cam to stop it from 'jittering' with looseness at low speeds, which makes for a very soft idle that wanders in speed. Almost 95% of the engines I rebuild also need to have at least 1 full turn (or 1/2 turn from each) cut off the spring(s) to restore the original advancer rate. They all advance too soon now, which makes for poor idle and dark sparkplugs when ridden in town a lot. On my own 750 I have it reaching full advance now around 3500 (cold) to 3300 (hot) RPM, and it is MUCH happier with modern fuels as the result: I took off 1 full turn from both springs to get here. Usually, by now the advancers are hitting full advance before 1800 RPM, which is much too soon and makes the low-speed throttle feel 'flat'.
Any tips for checking the spring health on my advancer? I cleaned and lubed the heck out of it
The best way is to use a timing light (and maybe an assistant) to shine on the timing marks to see if they "jitter" back-and-forth (the 2-3 side is usually the worst about this). There are 2 things (3, in a way) that can make this nervous-looking spark timing appear, and it hurts performance notably. This 'jitter' often will settle down to a not-on-the-(2-3)-mark at higher RPM, making it look like the advancer can somehow advance the 1-4 points OK but not the 2-3 points - which isn't physically possible if the points cam stays straight.
The first thing is: bent spark advancer shaft. This happens when someone turns the engine with that big nut right there, especially when cold, and particularly if turned CCW, with the sparkplugs in. (Honda realized how bad this problem was by 1970, then corrected it in all the later SOHC4 bikes...). The runout on that [bare] shaft should be no more than 0.006" with 0.002" being typical (0.000" if you can get it), provided the shaft itself is smooth enough to measure it(!).
The next thing is: if the spark reaches full advance before 2000 RPM, it is [much] too soon, especially with today's slower-burning gasolines. The gas is modified to still burn while entering catalytic convertors, which is somewhere around 8" beyond our exhaust pipes' ends(!). It should not reach full advance until 2500 RPM, and later is even better: mine reaches full at about 3500 RPM (cold) or 3300 RPM (hot) and it really cleaned up the sparkplugs, idle, and off-idle throttle control in traffic.
The final thing to check is the thin shim washers behind the points cam where it rubs against the advancer's backing plate. These started out as shim steel stock, 2 on each advancer, and many have 1 (or none) today, from wear. These shims do 2 things: first they ensure the points cam won't drag on the backing plate, making it stick during a slow engine deceleration like coasting. Then, they hold the outer face of the points cam squarely against the big flat nut that holds it to the crankshaft so it stays parallel to the advancer's center post (there should be likewise 0.002"-0.006" clearance there). If one (or all) of the shims is gone, the advancer cam can tilt a little, (usually) making the timing of the 2-3 points very erratic and dependent on engine speed: mostly it makes it hang a little with a higher-than-normal idle speed when slowly letting off the throttle. You can make your own shims from thin brass or even aluminum (not tinfoil) sheet. They don't have to be perfectly round ID or OD, just close enough to stay in place on the advancer's post. And, add a
small dab of grease to the post when you have this apart to prevent rust and sticking.
