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Evaporation System: canister replacement
This article covers the replacement of an evap canister on a GTS 250. Other scooter models should work similarly.

US versions of Vespa scooters come with an evaporative system. The purpose of it is to prevent escaping of overflowing fuel from the tank or fuel fumes from the tank into the atmosphere. Such fumes are considered to be carcinogenic.

The core element of an evap system is the evap canister, a black flat box filled with charcoal, which can soak up overflown fuel or condensed fuel from fumes. It will later release this fuel back into the engine when the engine breathes in air flowing through the canister.

With time, the canister will reach a point where its charcoal can no longer hold the fuel and fumes will "leak" from it into the atmosphere. That is when it needs to be replaced by a new one. My canister had reached that point somewhere around 28,000 miles and shown its end-of-life condition by the fact that my garage started smelling like fuel after parking my (hot) GTS in it after a ride.


Removal sequence


Take pictures of how elements are mounted before removing them. This will help to install them correctly later.

1. Remove the left side cowl panel for easier access to the air filter.
Undo one 10mm nut at the rear end and one black screw at the front end and then fold it out forward to remove it. Notice how the front comes out to make installment easier later.

2. Remove the black underseat cover around the gas tank filler neck.
Undo the gas cap, remove the plastic gasket around the filler neck,
undo the four bolts with a 5mm hex key. After removing the cover, replace the gas cap.

3. While you have the underseat cover off, check the two black Philips head screws for tightness (they hold the seat lock in place).

4. Remove the air filter cover to make room for taking out the evap system later. Undo six philips head screws from the side and two thumb screws at the upper edge.

5. Loosen the hose clamp at the filler neck overflow with a small screw driver, squeezing it into the omega loop to widen it.

Pull the overflow hose off the stem, remove the clamp (keep)

and feed the hose out of its two retainers.

6a. Free the hose off the brass elbow on the throttle body, on top of the engine.
That hose will run to the left and through the steel side wall. Just pry it off the stem for now and cut the zip tie near the brass elbow.

6b. Alternatively, if this looks easier for you to do, remove the other end of that hose from the evap canister while that is still mounted. You will identify it by its clear hose going into the canister bottom. View and operate from the underside of the cowl.


7. Remove the evap system.
7a. On some scooter models, it may be easier to open the rubber strap that holds the canister to its bracket. Can be done from the underside of the cowl. You will also see a big, round, white valve (the roll-over valve), which is attached to the bracket. This will need to be removed as well. If your scooter offers enough room down there to get these two items out, or if you can remove the other (black) hose from the evap canister and then only remove the canister box, then this will save you a bit of work. For me, this did not work and I had to go with 7b.

7b. To remove the bracket holding the canister and the roll-over valve, remove two 10mm nuts from the inside of the engine bay.
One nut is clearly visible, the other is hidden under the bracket that holds a fuse box and the relay switch. That bracket can be removed with an 8mm (top) and a 10mm (bottom) wrench.
Once removed, you have access to the lower 10mm nut for the evap bracket. Push in both threaded bolts of the evap bracket and remove it from the underside, carefully pulling out any hoses that you still have attached.



8. Remove any attached hoses from the canister and replace it with a new one (around $50). Reattach the hoses. If they are too tight, loosen the clamps with the small screw driver and later squeeze them tight again with a side cutter (careful not to cut the omega loop) or replace them with a worm gear clamp. I managed to reuse all the OEM hose clamps and still have firm hose connections. A small amount of soapy water over the hose stems will help with reattaching hoses.

9. Reinstall all parts in reverse order.

Photography: courtesy Salima Draghetta
Last Updated Mon, 19 Nov 2012 05:16:17 +0000

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