Modern Vespa

What are the signs that a belt is about to go?

The last two times I've had my 2006 Piaggio Fly out for a ride, I noticed an odd "blip" at WOT. First time happened on previous ride; I have a pretty steep climb that, on my Fly, I generally max out at about 35mph by the time I get to the top. On the flats heading into the hill, I was at WOT trying to max speed, and for about half a second, it felt like I lost all power-- not an engine stall, but just a momentary power loss. I rolled off the throttle thinking I'd stalled; I hadn't, so I rolled back on the throttle and away we went. I figured maybe I'd just meet the rev limiter for the first time. (I'm a new rider btw, if that's not obvious!)

Today I had her out again, and I experienced this "blip" 3-4x today. Always at WOT, trying to gain speed on a hill. However, today when it happened, I lost power-- rolled off throttle-- rolled on throttle at lower RPMs, and it did it again, like 3x in a row, each about 1/2 - 1 second of power loss. I was maybe at 55mph indicated when it started For the rest of my ride home I kept it off WOT, and it was fine.

Might this mean I need to change the belt/rollers? The scoot only has 2,000 miles on it, I bought it used last year. I'm guessing it's the original belt, so it would be 15 years old. I'm sure it can't hurt to change the belt even though the miles are low, but might the belt be causing this odd power drop at WOT?

Sounds like you might be bumping the rev limiter.

If this is at a lower road speed than normal, could be a worn belt or malfunctioning variator not coming up all the way to "high gear".

Hard to determine whether the belt needs replacing based on performance. It is even hard to tell with the belt in your hand unless it is badly cracked or badly worn. Most of us replace the belt and rollers when due or a bit earlier. Having a belt break while riding is an experience most try to avoid. Given the age of your scooter - and of the belt - I'd probably change it now and start the clock over again. Rubber parts don't last forever.

I sort of understand the belt. What are Rollers?

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I'm not convinced it's the rev limiter... I've put about 600 miles on this scooter since I bought her last fall, have had many instances of "flooring it" up some big hill climbs around here, and the last two rides were the first times I've experienced this phenomenon.

I will probably go ahead and replace the belt regardless (it can't hurt!)... I have not had a chance to watch any videos on it yet, hopefully it's a fairly straightforward job?

At 2000 miles it due a belt and roller check. And with that age replacing the belt is arguably a good idea, regardless of milage.

I had weirdness in response on my 10-year-old belt on my S150 after I bought it with only 1700 miles. Seemed to happen at high speed after about 15 minutes or riding. I don’t know if it was glaze or stiffness from age but the issue went away after replacement.

I also replaced the rollers, which appeared to be in perfect condition except for a few spots of dirt.

I suggest that anyone with a belt that is or even might be more than 7 years old replace it BEFORE these problems or actual belt failure pop up. Of the many things to worry about while riding, a belt shouldn’t and needn’t be one of them.

Your problem has nothing to do with the belt or rollers so you would be better served by fixing the issue than doing unnecessary work like changing the belt on a 150 at 2k miles. Fix it first, then maintain it after you have a well running bike.
If you replace something that's not part of the problem, then find out the bottom end was about to grenade, you will end up with brand new parts on a blown motor. That feels dumb.
That's most likely not your problem, nor are the valves out of adjustment or something seafoam can fix.
It sounds like a fuel delivery issue. The first thing I would do is make sure the spark plug or spark plug cap aren't broken and are properly connected. Check to see how much of an air cleaner you have left. If it looks fairly new, that means someone has likely been into the engine before, probably more than once to clean the carb on a 15 year old bike with 2k miles.
Then, check, or more likely replace the vacuum lines and make sure there aren't air leaks in the intake tract. I think that's where your problem lies. If that doesn't solve this, it's likely to mean a carb or fuel pump issue.