Saturday, January 23, 2010

Sito and the extra ten

After speaking with another VBB owner I decided I would spend a little time and money to improve the performance of my Vespa. As I didn't want to invest too much money I bought a second hand (but unused) Sito PX exhaust off ebay. The original VBB exhaust was a very simple affair and didn't really add to the performance of the scooter. Sito built larger bore exhausts that improved the gas flow through the engine. While this doesn't substantially increase performance in the same way as a racing exhaust would, it does offer an improvement without requiring changes to the carburettor or jets.
The new Sito exhaust is in front, the old VBB exhaust is at rear
Replacing the original exhaust is a very simple affair and the steps are described in detail here so I won't repeat the instructions:

What I will say however is that it was a revealing exercise into the dodgy world of Asian scooter restorations. The exhaust itself came off quite easily but the bolt securing the exhaust to the frame was very difficult to remove. The restorers obviously did not have the correct size bolts to hand and so used a roofing bolt that was overlength and a little too thin. To make it fit they'd used about six washers of different sizes with bolts in front and behind the connection to keep it tight. They'd obviously installed the exhaust before the engine and swing arm were in the frame as they'd threaded it from front to back. This meant I couldn't extract without removing the whole engine as the bolt was butted up against the frame. Instead I chose the dodgy mechanic's method and just cut the through the bolt.
It is much easier to get at the securing bolts with the rear wheel off.

There were signs of poorly welded repairs around the bolt hole. Obviously someone had smashed the bolt (and exhaust) out of the swing arm and then re-welded the damaged hole so that a new bolt could be re-threaded. Nice.
Dodgy bodges. A roofing bolt, the wrong size, threaded through from the front through a hole that has obviously been hacked about and re-welded.

The Sito exhaust slipped on easily but I suddenly found that it was missing the securing bolt. This led to two trips to the hardware shop for new bolts as I made the mistake of assuming the new securing bolt would need to be approximately the same size as the old one. That was a wrong assumption as it turned it. The end result though is that the new securing bolt is much thicker and sturdier than the old one.
All in all, if it wasn't for the problems caused by the dodgy repairs, the whole job could have been completed in 15 minutes.

So, did it work? The first thing you notice is the Sito gives off a deeper tone than the tinny old exhaust. It did not really improve take off speed but as I worked up through the gears I found the old girl was able push on through past the 40, 50 and finally 60 kph barriers much easier than ever before. For a few minutes the needle even waivered towards an unheard of 70 kph so from my perspective this has been a very significant improvement.


  1. Sounds good Paul, I wonder if this would work on my VNB???

    John D.

  2. Hiya John. I'd say yes that would work. The Sito plus exhaust was originally built for the PX but just happened to fit any large frame Vespa. As there really isn't any difference between the VBB and VNB engines it should easily fit.
    I was originally going to buy this one but one came up on ebay closer to me so I bought that one instead.