Modern Vespa

I have installed the Malossi 190 kit and exhaust on my 2016 Sprint. The DB killer is installed.

The Forcemaster is set according to the installation instructions, and the scooter will often (if not always) backfire lightly when decelerating. It also smells surprisingly like my 2-stroke Lambretta. It's not smoking or using oil, so I assume it's just the exhaust emissions.

Is there an optional catalytic converter that I am missing? I was under the impression that the exhaust is homologated with the DB killer installed, and the stock exhaust does have a catalyzer, correct? I don't remember the scooter being objectionably smelly before installing the cylinder kit and exhaust (both were done simultaneously).

Just curious if there is something I can do to address both the backfiring and the odor issues. Thanks!

Running an engine rich is A LOT safer than running an engine lean. My guess is that the kit is maybe setup a bit richer on the fueling side of things.

Running rich fuel through a catalytic converter will mean the cat doesn't have as great a lifespan.

It might be worth seeing if you can find a tuner who can manually adjust the fueling in the ECU?

which exhaust part number did you buy? for the gts they sell with and without the cat and I'd assume the same for the sprint. (way more expensive with the cat).

simply having a db killer is not what makes it homologated.

yes the stock has a cat

https://www.scooterwest.com/malossi-performance-exhaust-vespa-sprint-primavera-m3216551.html

This is the exhaust that I have. No mention of a catalytic converter so you're probably right about it being a different part number.

yup, no cat according to https://www.malossistore.com/en/gb/rx-black-exhaust-system-3216551-P


it can be bought separately https://www.malossistore.com/en/gb/homologated-catalytic-converter-for-rx-black-or-maxi-wild-lion-exhaust-system-3216715b-P

The regular Malossi Performance Exhaust has a cat available, but it's about $160, so by the time you add that to the price of the Malossi Performance Exhaust, you can get a Malossi MHR Racing exhaust. It's all carbon fiber, and it's about $600. Malossi doesn't have a lot of them in inventory and I'm not sure if they are going to continue making them available after they sell through this inventory.

Here's a link to the Malossi MHR Racing exhaust. It is a thing of beauty. Not the link, the exhaust.

https://scooterpartsco.com/prima-150-exhaust-c-3637_3649_3963/malossi-mhr-racing-exhaust-for-vespa-primavera-sprint-150-p-25143.html

Thanks for the info; that exhaust is a looker for sure! Since I already have the standard Malossi exhaust however, I think I'd be inclined to just add the cat to it.

Are you able to get one? I will gladly place an order if so.

I like the way my exhaust sounds with the dB killer installed, but I wouldn't want it to be any louder because I live in a townhouse complex, and I often leave for work before the sun comes up...trying to be a decent neighbor.

My main motivation for adding the aftermarket exhaust was to avoid removing the header every time I need to change a rear tire.

Thanks for the responses everyone

the slip joint on mine seized so I take the exhaust + midpipe off each time just like I would with the stock oem exhaust. I could probably with a lot off effort break the seized joint free but can't be stuffed as it would probably seize again. and yes I used anti-seize on it (and also the clamped joint where the mid connects to the header)

I added the catalytic converter I got from Scooterpartsco this week--thanks Motovista!

https://scooterpartsco.com/01-malossi-master-part-list-c-170_180/homologated-cataytic-converter-for-exhaust-s-maxi-wild-lion-p-14669.html

It's a tight fit, but some liberal used of a heat gun and plenty of anti-seize finally got things where they needed to be. It does indeed eliminate the occasional backfiring I was experiencing, as well as the offensive odors.

Subjectively, I would say that it might have robbed some performance, but that perception may just be due to the somewhat quieter sound.

As is typical with many aftermarket parts, the documentation that came with this part was minimal, mainly consisting of proof of emissions homologation. If you decide to add the catalytic converter to your Malossi or other Arrow-built exhaust (the cat is made by Arrow), you might find this info helpful:

- There is a ring or flange that is welded to the outside of the cat. It is not centered along the length; the shorter portion of the cat pipe goes inside the header, while the longer portion goes inside the muffler.

- I found it best to fit the cat first to the muffler, and then fit the muffler to the header pipe. I used a rubber mallet to tap it into place; a small portion of the cat still protrudes from the muffler when it is all the way in.

- With the cat installed into the muffler, the cat goes inside the header pipe, while the muffler goes around the outside; effectively, the header pipe is sandwiched between the muffler and the cat. If the cat is not centered, the header will bind, but a few taps with a mallet will allow the gap to be evenly adjusted before installation.

- As is the case when changing bearings, it may be helpful to place the cat in the freezer overnight to help increase available clearance for installation. I didn't think to do this, but it would have probably made things easier.

I completely neglected to take any photos of the installation

With my Arrow i initially installed without the cat and then added it for the same reason.

I found the opposite install order was easiest: cat into header then into muffler.

I attempted to do it this way first, but couldn't quite get things aligned without resorting to the mallet...I figured it would be less strain on the header pipe to tap the cat into the muffler vs tapping the muffler onto the cat/header, if that makes sense.