Modern Vespa

I recently changed the muffler on my PX-150e and just want to share my experience.

There are a couple of helpful videos on YouTube that show how to do this job. And it's relatively easy with a stock replacement part of the same dimensions. Can be done with basic tools and takes around one hour.

Steps

Remove the bolt that clamps the muffler to the exhaust port.
Slightly lift the back end of the scooter with a jack or block.
Detach the rear wheel from the hub and slide wheel backward.
Remove the long bolt that attaches the muffler to the frame.
Wiggle the old muffler until it comes off.
Reverse the steps to install the new muffler.

*Make sure the new muffler is firmly seated to the exhaust port before tightening the clamp. There should be around a 3cm overlap.

Result
The new muffler worked great, but I was a bit disappointed that the motor was just as loud as before. My PX seems to be louder than most, but apparently that has little to do with the muffler.

It took me a few minutes the other day to swap one and I wasn't at full speed but I had my son leaning the scooter for me and I was using Milwaukee power tool which cut down the time. I have done many of them. Some times I literally swap a few back to back and test them for speed trials and acceleration testing.

My 2 biggest concerns are always: 1) gas 2) the nut behind the enclosed metal box on the back of the exhaust.

When you lean the bike it tends to flood even if you close the gas tap. For that reason when I swap the muffler I empty the gas tank.

As far is the nut hidden on the back of the exhaust and tucked up I always use a scribe to line it up with the bolt while I continuously rotate(tighten the 3"-3.5 bolt).

There is no "true book" that tells you how to do it. I am being sarcastic because I do have the P series manual and you might as well keep it in the drawer. What you have to worry about is mostly lining up the nut in the back of the metal box.

Another thing to do is use a rubber mullet to tap the exhaust to also slide it on the cylinder exhaust spigot.

The last time I changed my exhaust I was having a miserable time getting the bolt to go into the nut.
I got a little bit longer bolt and tapered the end on a grinder.
Went straight in, no problem.

Yes, that is correct and it can happen(will happen) to everyone. The main problem is that the nut or the square with the thread(substitute of the nut) moves around a lot inside that metal welded "cage" or "metal box".
When you think that you are screwing the bolt into the nut what is really happening is that the bolt just pushes in but the nut or square with thread is most of the time misaligned or completely lose.

The steady solution that I found that works for me every time is to just hold the nut with a scribe or with a long thin screwdriver. You just hold it in place enough for the 3.5" bolt to grab the first tread. Even after it brags the first tread you still need to hold the nut inn place as it will turn in the same direction of the bolt as you are trying to tighten it.

Just holding the nut in place with a scribe or with a screw driver is enough so that you can actually tighten the bolt. I personally learned the hardway. This use to be a PITA but no longer is for me.

The design is mediocre because the backing nut moves around and doesn't line up.