Modern Vespa

I recently decided to put in a big bore kit (80cc) into my 2006 LX 50 45T/2v. It runs well, but at wide open throttle it has a frequent, but inconsistent scratching noise that I assume is spark knock, although I'm not certain.

I don't fully remember, but I think it did this with the old piston as well, although much quieter. I don't want to damage the engine, so would appreciate any insights.

Before I drop the engine and pull it all back apart again to check for piston damage, I wanted to see if anyone had other thoughts. Here is what I've tried so far:

1. I switched back to the old spark plug (had put in an Iridium
2. Double-checked the valve lash
3. Tried a higher octane fuel (US/93)
4. Tried a different jet (stock is 75, the kit came with a 79, tried up to 90 but it would backfire and didn't run well).

I had also replaced the CDI around the same time as the bike would stop running when it was hot. I had also previously put in the Malossi Multivar kit and variator slides. Everything else is more or less stock.

Thanks!

I have an '07 LX50 and installed the Malossi 78cc kit + Power Cam a few years ago. For the past year or so I get a little pinging sound at idle which abates immediately above idle. Runs good otherwise. I think my problem is piston slap from running too lean. I'm using a 36 idle jet with an 82 main, and not sure how I managed to run lean, though I am the world's worst carb tuner. I bought another Malossi 78cc kit an plan to install it soon, and just do everything I can do to not run lean in any way going forward.

The old 49cc piston I removed has scuffing on the lower part of the skirt. Did it slap too? Why the scuffs on the skirt, what happened?

I ride this scooter very hard and use it to get around almost every single day in an urban environment. I do keep up on the maintenance, which is much more intensive after the BBK. It uses roller weights up rather quickly, and the clutch just could not handle it for long so I had to upgrade that as well.

I'm thinking now, that doing these BBK upgrades are probably detrimental to engine life. Well duh. A better solution would have been an engine swap to 150cc.

So what do you mean by 'scratching' sound at WOT?