Modern Vespa

I've been trying to figure this out for two years now. My 2005 Stella never gave me an issue. I usually rode far forward on the nose of the Stella, and of course the handlebars may be higher/lower/wider/narrower/etc than the GTS Super 250.

I'm 5" 9" but with short legs that just reach the ground on the GTS. I've tried riding forward on the "horn" of the seat, in the lowest point of the saddle, and towards the back. My left shoulder blade starts to hurt after a few minutes and just stays that way.

My latest theory is that I should be on the front part of saddle , but the "horn" is rotating my hip backward causing rounded shoulders. Sitting farther back would also cause rounded shoulders. So this would mean having Pirate or someone doing a flat front saddle, but that's a lot of money to spend on a theory.

Has anyone had this happen to them? Or any thoughts or brainstorms? Or a cheap modified GTS or even maybe a GTV saddle to try?

Once the cause is isolated a few MVers have had their scooter seats modified or 'shaved'.
Try these 'back pain' threads for size...
Good luck.
Back Pain

[SSR] bloody back pain...

Back Pain

Back pain and scooter riding

Thread on Back Pain

Some here have been happy with a Corbin seat. It helped my back but I like to slide back on my seat, so for me a GT200 seat is the most comfortable and allows shifting positions without sitting on a hump. Shop around they can often be had for under $100!

I was having back pain on my scoot too. However, mine would only occur after riding for an hour or so. I found that, like on the ground, I was slouching, partly because I am short. I now find if I use my stomach muscles to keep me sitting straight as opposed to my back muscles, I don't get the pain. It's important to relax the back and shoulders too. Good luck.

Many of us GT200 owners removed the little transverse strap from the seat coz it contacts your tailbone and was a literal pain in the butt.

If you're still interested in cutting down your seat:
Seat & seat pan mod for the vertically challenged

I never had any shoulder problems but the Corbin seat made riding 100% more comfortable.

I got the hump shaved down and a new seat cover made,it's made a huge difference,cost $100 nzd

make sure the handle-bars are on perfectly straight - 1 degree off will stuff your shoulders and back after a while !!

Cutting down and narrowing your seat and ensuring that the front part is level might help. Riding with your back too rounded (kyphotic) can cause some to have low back pain. Getting your seat such that you can sit in a more forward upright position without having to bend forward to reach the handlebars would probably help your problem.

i hav found that sitting up straight helps my back pain,my pain feel like someones stuck a pin into top of my spine,

What Benny said. Find a local upholstery shop that works on motorcycle seats and get yours shaved down. Even small changes make a world of difference.