I've got a 1964 Li150 series 3 that I bought recently. It's my first Lambretta so I'm still learning about them.
Previous owner had it newly built with this:
Stock cylinder bored out to 175cc
Jetex sh2/22 - 115 Main Jet
SIL electronic ignition
Casa Innocenti-stamped s3 exhaust (the non mushroom type)
I've got the bike tuned pretty good through the low rpm range and it pulls great, but when I hit high rpms there is just this crazy rattling noise/vibration coming from somewhere. It goes away the second I shift to the next gear, and also goes away when I pull the clutch and rpms go back down. I can also sort of hear it revving on the center stand, but I don't like to do that for terribly long.
It sounds like it's coming from within the meat of the scooter under the seat, not inside the shield or headlight housing or anything.
At first I associated it with rich 4-stroking, since the previous owner had a 115 main jet and said he jetted it rich for break in, also I'm still learning what lambrettas sound/feel like when tuning them. I've lowered the main jet to 112 and now 110, and it hasn't cleared up (yet). I might just try a 100 briefly just to rule that out.
But I'm starting to wonder if it's something else.
I know this is a ridiculous question, because sounds/rattles can come from anywhere, but I just CANNOT find it. I've leaned the bike over with the engine running and revved, and looked for things rattling, emptied my tool box, removed the side panels (of course), ensured it wasn't the center stand. I am just getting stumped here.
What else could it possibly be?? Part of me is just "ride it till it stops making noise or breaks"
Any advice would be great.
Thank you!
