Left Hand Polini Exhaust - Small Frame Vespa
Putting on a Polini exhaust for a small frame bike is a pretty easy job but there are a few things to know. Firstly here is what is included with the pipe:
The first step is to remove your old box style exhaust which is held in place by a single 17mm nut at the swing arm and another two 10mm nuts which passes through the swing arm. The swing arm bolt is a little annoying as it will almost come out but then hits the rear tire. You can either deflate the tire or remove it to get this free - I removed it for the pictures and then installed it again right after the exhaust was removed as the Polini doesn't have the same bolt problem.
Once the swing arm bolt is removed you'll need to remove the exhaust stub bolts. Follow the exhaust tube up until where it hits the cylinder. These are a pain in the ass to reach when the motor is in the frame, but I had mine out when these pictures were taken. You may need to remove the cylinder shroud to get access to the two 10mm (arrowed in green) that connect the exhaust elbow to the barrel.
I also replaced the barrel with a Polini 130cc kit on the bike I was working on. The weird thing is that the one of the Polini bolts on the Polini barrel is too long to fit the Polini exhaust. I don't think this is the case with the standard barrel studs. I had to grind the one down on the right as well as the nut to make a shorter nut and stud. If you need to do any grinding make sure you stuff a clean rag in the exhaust port to stop any bits flying into the combustion chamber.
Fit a new exhaust gasket and then bolt the first exhaust tube in place using two nuts with lock washers to hold it in place. The shot above shows a slightly out of focus image of how I needed to grind the nut and bolt down to fit.
Get the expansion chamber part of the exhaust and carefully slip it into the exhaust tube bolted to the barrel. This is a nice tight fit so there shouldn't be any reason for exhaust tape or other sealing compounds.
Then loosely refit the exhaust swing arm bolt and pivot the expansion chamber slot so that the bolt passes through it. Once it slides all the way in, tighten the single bolt.
I found that the slip joint at the two pipes didn't slip in all the way but it did go in enough to make a good connection. I suppose you could bend the swing arm mounting bracket a bit if this bothers you. Next, fit the single spring to one side and stretch it to the other hole. A strong hardened metal hook is a great tool to help save fingers and knuckles.
Your motor should now be good to go. Polini doesn't give any insight to whether or not the standard carb jet should be changed for this pipe. The difference between the standard and the Polini exhaust is not really apparent except for the different exhaust pitch, until you open it up. It allows the engine to rev much more smoothly to what feels like a higher RPM. Overall it seems like a well priced, well finished pipe that delivers decent performance for the money.