Modern Vespa

Hi All
My Sport City 250 is developing a vibration under load. I do have some clutch shudder on pull away and at low speeds, but this vibration is when you open the throttle at 40+ mph? If I open the throttle fully at say 40mph I feel a vibration come through the whole bike. If i back the throttle off it goes. It does seem to lessen in severity at 60+mph? Any ideas on what the cause of this could be?

Bike has covered 19k miles and I fitted a new belt and Dr pulley sliders at 17k miles.

Wheels need balancing and/or your steering bearings need to be adjusted.

Wouldn't the wheel balance be there regardless of throttle load though?

Depends if it's the front or rear that's off - and most imbalances can be 'ridden through'. Depending on circumstances (including rim size), this can be anywhere in the 40-90mph range - and the vibration usually only exists in a 20mph band.

There could be other things setting up in resonance, but wheel balance is a good and cheap thing to check, especially if you take the wheels off yourself and take them in.

I started a thread about this same thing last week, then noticed someone else had the problem on yet another thread calling it shudder instead of vibration. I'm not at all sure this has been addressed. People have suggested the cause might be the belt, rollers, dust, humidity, causing it. I can tell you mine is getting much better. What I did was ride my bike hard...80 mph on the interstate with some fast acceleration. Problem solved. I don't know what that did, but it reduced the shuddering, lugging, vibration, whatever you want to call it. Maybe mine wasn't broke in yet. It just has 635 miles on it now. Your problem sounds a little different though since mine was only at slow speeds under load, just taking off. The steering head problem is very common and that does sound more like your problem. Several YouTube videos on how to check for that.

Thanks Guys, this gives me something to hunt around for over the weekend.

I took the bike for its MOT (UK annual inspection) yesterday. The MOT tester noted there is slight play in a round engine mount on the right hand side. That might be causing the vibration, or at least contributing to it? Looking at the parts fiche on Suttons website I cant find it? Has anyone replace done of these? Hopefully its a frailly straightforward job, or is it a PITA?

I found it its called a "Silent block" and is an anti vibration damper. So it obviously could well be my problem.