For those of you who are interested in getting a little more top end on your Honda PA-50s, here's a fairly easy modification you can make to your variator. I have personally performed this modification on my PA-50 and it added about 10-15km/h (6-9 mph) to my top speed without noticeably impacting my acceleration.
Although the photos and instructions presented here are mine, I cannot take credit for this idea. I got the idea from a guy named Gangly Jeff. His website is here: http://www.geocities.com/MotorCity/Factory/1935/
HOW THE MOD WORKS:
Variators are an interesting way of keeping an engine within its power band at varying speeds (hence the name). On Hondas this works by using two cone shaped pulley sheaves that are pushed together or pulled apart to change their diameter with respect to a belt that runs between them. A second spring-loaded pulley in the rear (picture 1) takes up the slack in the belt as the diameter changes up front. This system works exactly the same way (from a physics point of view) as gearing in a traditional transmission, except there are an infinite number of graduations between "low" gear and "high" gear.
To see how this works, take the cover off the side of the moped and start it on the stand. Rev the engine a few times and watch the variator. Pretty nifty, isn't it?
In order to keep the top speed of Honda PA-50s down, Honda engineered the variator to "stop" at a certain point. The modification described below will allow the variator to continue working a little further than stock allowing you more power at the top end.
The mechanism that forces the pulley sheaves to open or close are simple weights that run on a curved track (picture 4, round thing on right side). As the pulley turns faster they push against the sheave via centrifigal force and force the pulley to close. If they are allowed to travel further along the track, the "gearing" can be pushed a little further.
1. Consulting the first photo. The variator is the pulley contraption at the front of the bike. Take it off the bike. If you can't figure out how to do this, you shouldn't be modifying your moped's transmission.
2. Pictures 2 and 3 are illustrations of what the modified variator will look like. Cut notches just like the ones you see into the outside sheave. You want to make them big enough so that the roller weights (see image 5) can roll a little further into the gap, WITHOUT falling out. Don't even think of trying to do this without power tools! I used a Dremel with a cutting disk to make the notches.
3. Disassemble the variator (see picture 4). Remove the retaining clips. You don't need them, and they'll prevent this mod from working. Clean everything very well. Get all the dirt out of the variator. The variator in this picture is unmodified and obviously needs to be cleaned --so don't use it as an example of "clean".
5. Take the roller weights out and fill them with lead (either solder or pound lead fishing weights into them). You want to make them a bit heavier, but not too heavy or you'll lose a lot of your acceleration.
6. LIGHTLY grease the roller weights and curved tracks inside of the variator before you put it together. Use very little grease or you'll wind up with a ruined pair of pants when you start your ped. Do not put the retaining clips back into the variator.
7. The rear spring loaded pulley (picture 1) should be lubricated at its center. Clean the sheave faces with solvent to remove any oil from them (you only want to lubricate the inner mechanism).
8. Reassemble everything. You might want to fiddle around with your belt tension.
If you try this mod, let me know how it works for you.