Help me diagnose my scooter problem

February 2, 2015 5:28 AM

I have a piaggio FLY 125cc scooter (automatic transmission) that started having problems the other day. I'm keen on trying to fix it myself but not sure where to start. More inside

The problems started after a recent trip to the airport. My drive to the airport is 20 minutes where i'm going full throttle the entire way. My scooter normally does about 100km tops (60mph). Normally, I don't get the scooter to top speed for such long periods of time. When I came back from my trip, the first thing i noticed was that before i turned the ignition, it was much more difficult to move the scooter backwards to back out of the space I was in, as if the back tire was engaged in gear. It started fine and I took off so I didn't give it much thought. Then, as soon as I stopped at a traffic light, I noticed that with my hand completely off the throttle, if I let go of the brake, the scooter wanted to move forward. It wasn't slightly, it was noticeable. Without doing anything it would move forward about 5mph. This never happened before. If I applied the brake, the engine would sputter and stall. It's as if the throttle was still engaged. That was the other day. This morning when I went to start it, it was cold out, maybe 4ºC and it took various attempts to start the engine. Even when its cold out this isn't usual. Especially since I have a new battery with plenty of cold cranking amps avail. I could also hear the engine sounding differently.. hard to describe but didn't have a normal purring but rather starting to sound like what old vespa LXs sound like. For the first 15 minutes of my ride, the scooter would not top 30kmph. Once it got warmed up, it went fast again and accelerated properly but with the same issue with the throttle and stalling i mentioned above.

So.. those are the symptoms. From what I read online the first thing i'm going to try is to change the spark plug since that seems to be a common ingredient in many problems. I also suspected that perhaps the throttle cable is out of whack but it would make more sense for that to result in a reduced top speed rather than it not disengaging at its loosest position.

Any ideas?

many thanks in advance

posted by postergeist to Travel & Transportation (9 answers total)

Is it still under warranty? That sounds like a transmission problem, not an engine problem, and possibly expensive to fix. I'd check the fluid level and condition, and maybe top it off/change it because that would be relatively cheap and easy. But I'd also be thinking about how much it's worth spending on this, so I'd know when to say when.
posted by jon1270 at 6:29 AM on February 2, 2015

Okay, further research suggests the transmission isn't anything like a car's automatic tranny, so forget what I said about the fluids. This might be the service manual for your bike. I'd focus on the sections relating to the clutch, because the problem seems to be that the engine isn't fully disconnecting from the wheel when it's supposed to.
posted by jon1270 at 6:51 AM on February 2, 2015

Response by poster: That may be something to look at yes. I know the abrasive clutch pads are housed inside a bell-like structure that has weights distributed such that when the disc starts spinning the clutch engages and spins the wheel. If the springs are caught or its not disengaging, that potentially could be a reason the wheel keeps spinning even when the throttle is let go. But again, i'm no expert. I am handy though so its one of those things I'm eager to fix myself, even at the expense of doing it wrong and having to take it to the shop anyway.
posted by postergeist at 7:00 AM on February 2, 2015

It looks like a basic centrifugal clutch, which I'm familiar with because I work on chainsaws as a hobby. The bell/drum is connected to the drive wheel, and the moving weights are connected to the engine, with springs pulling the weights inward. At higher RPM's the centrifugal forces on the weights overwhelm the springs, the weights move outward and grab the inside of the drum, causing the wheel to move. At lower RPMs the springs are supposed to pull the weights back in, away from the drum, so the wheel can stop moving while the engine idles. I'd say that either one or more of your clutch springs has failed, or some other fault is preventing one or more of the weights from returning to their idle position.
posted by jon1270 at 7:10 AM on February 2, 2015 [1 favorite]

My scooter (People 50, 2005 model) would do the same thing, and it was all spark plug related. You can take a metal file and file off the gunk and re-gap the plug, although plugs aren't that expensive so you can just switch it out, too. Make sure the gap is correct -- if mine was off even a little it would cause all sorts of wacky problems.
posted by danielle the bee at 7:11 AM on February 2, 2015

There's no way a spark plug problem would make it hard to walk the bike backwards with the engine switched off.
posted by jon1270 at 7:12 AM on February 2, 2015 [2 favorites]

The Piaggio Fly 125 has a CVT, which is a belt driven transmission. The fact that the bike wants to move forward at idle and was difficult to move backward could indicate that the belt is not able to disengage from the pully. This could be due to a broken clutch spring or a stuck roller weight. Take a look at http://modernvespa.com/forum/wiki-cvt-principles-how-it-works-how-to-improve-it-

The difficulty starting is most likely an old spark plug.
posted by Gungho at 7:21 AM on February 2, 2015 [1 favorite]

Agreed that the clutch (or CVT) is not disengaging properly. The difficulty starting is likely also related as the extra drag of turning the transmission against a slight drag slows the cranking speed, which makes starting harder. The symptoms are all consistent with a dragging clutch.

The top speed limitation is likely a result of the same thing. Everything points towards the clutch (or equivalent) dragging to me.
posted by Brockles at 7:42 AM on February 2, 2015 [1 favorite]

Response by poster: Thanks everyone. I think general agreement around the clutch sprint assembly. Fortunately I've seen this taken apart and done many times so i'm confident I can give it a go. Now all I need is that special tool to take the flywheel off. :(
posted by postergeist at 8:02 AM on February 2, 2015