Modern Vespa

I have a question about my new GT200. From the information I've received on Modern Vespa as well as things I've read elsewhere, including Vespa's web site, I expected my scoot to acheive at least an indicated 75 mph, which would be roughly 68 actual mph. My personal experience, however, does not bear this out.

When doing a top speed run on a flat surface, my scoot tops out at 60 mph indicated, which is probably around 54-55 mph actual, far short of my expectation. I should note that I live at 5300 ft altitude, so I know that the engine makes 20% less hp than it would at sea level, but the thinner air is also easier to push through, so I wasn't expecting the hp deficiency to have such a drastic affect on the top speed. While a differnt animal, my experience with automobiles at 5300 ft is that the acceleration rate suffers as a result of the higher altitude, but the top speed does not.

I should also note that I did my top speed run in the standard sitting position -- I made no effort to tuck down in an effort to streamline myself. Perhaps the advertised and discussed top speed on these scoots is a function of a rider in a tucked position.

The only other thing I can think of is that the scoot is running too rich as it has not been rejetted for my altitude. While a rich condition can rob power, I did not anticipate such a pronounced effect -- particularly since the scoot seems to run perfectly otherwise.

So, am I expecting too much out of this scoot, or is something else going on? Any thoughts?

Thanks.

-Dave

Wow, that doesn't sound good. My stock GT200, with a 220 lb rider, top case and medium windscreen has held me at 74 MPH GPS (something around 80 indicated) on a flat highway (app 1000 ft altitude)

If you've read this forum even a small windscreen can help top speed.

Does it 'sound' like it's struggling up at max speed at all?

Thanks lomuchi. The answer is no, the scooter doesn't sound like it's struggling at all at top speed. It just won't go any faster. 60 indicated is pretty much it.

-Dave

That doesn't sound good. here is what I got on my way to work this morning. no wind screen, no tuck just me and my gt200 in the fast lane! my top speed is in the lower left hand corner. 75.6 mph

I think it's the 5300 foot altitude. Tiny carbureted motor at that height? Yeah, that's it.

Hi.
I also live here in the Denver area (near Chatfield reservoir, which would put me at around 5500' elevation). I have a Derbi Blvd 150, and a Vespa LX 150 (both have the same engine). On level ground with the Derbi, I top out at an indicated 62 mph (don't know what the "real" mph is). With the Vespa, it's approximately 57 mph. The Vespa has had performance issues from day one, so this number may be meaningless. Also, I just had it worked on again (some issues were identified that could definitely affect performance), but I haven't had a chance to test it yet since the work was done.
I would expect your scooter to do better than it has, assuming it's completely broken in. If it's not, you could possibly see an improvement up to about 3000 miles.
Hope this helps.

You were right on target.

You need to rejet for altitude and yes, that does make a big difference in performance.

^^^ Ditto ^^^

You need to retune the carb to compensate for the elevation. Less air means less power and a richer mixture. The vacuuum carbs (like the CV carb on your GT) can adjust to an extent, but not anywhere near as well as fuel injection can.
Some things you can do:

Screw in the idle air screws and/or; Lower the needle position and/or; Reduce the size of the main jet.

Bottom line is you are not going to produce the same power at 5300 feet that you would at 1000 feet, er go, your bike will not go nearly as fast as it otherwise would at a lower elevation.

I beg to differ with the comments about rejetting (not with the theory, of course, but with the results you can expect).
I have never rejetted the Derbi, and we do ALL of our riding between 5500' and 11000' elevation (our rides average about 7700'). But I did have the Vespa rejetted in the hopes of correcting the performance issues (from a 92 to an 87 jet, IIRC - not really sure of this), as recommended by the dealer. Results were that the performance improved slightly at our normal riding altitude (still never as good as the un-rejetted Derbi, which also happens to be 50 pound heavier than the Vespa), but there was no noticeable difference in performance at 5500'.
My take on these results is that the scooters, as delivered (supposedly jetted for near sea level at the factory) are capable of better performance than you're seeing, even at 5000+'. I suspect that the Vespa's performance issues are not related to the jetting. My dealer (Erico Motor Sports in Denver, where I presume you purchased your scooter) has been more than cooperative in helping me resolve this issue, and I have high hopes that this latest service has corrected the problem (let you know after hitting the high country this weekend, weather permitting).
Keep in mind that my experience has been with the 150 engine. I don't know how (or if) this translates to your engine.

If you've read this forum even a small windscreen can help top speed.

Where can I get these magic windscreens that boost speed by 20mph?

I live in the Boulder area, have a gt 200 with roughly 2,000 miles in it, have not had it jetted and no windscreen and defenetly get it to the 75 mph indicated line. And no not only when im going down hill. so i would say its more of a mechanical issue than jetting issue, even though jetting might help, erico motorsports im sure can help you but its going to cost you. I wish i new how much it cost to get the carb jetting maybe then i would consider it, or try to do it myself if i knew what it entailed

You don't say how old or how many clicks you have on your Scoot.
My GT is 2003 and regularly serviced. if it was performing as poorly as yours I would be straight to the (Vespa) Doctor for a checkup.

The scoot is brand new with only 50 miles on the odometer. I know it isn't broken in yet, but given what I read in the owner's manual, 60 indicated should be just fine for a new scoot (75-80% of top speed during break-in).

I assume that the scoot will loosen up with mileage, but I wouldn't expect it to gain an additional 20 mph.

Thanks to everyone who has replied. Also, it's great to hear from some local scooter owners as it gives me a solid reference point.

One last thing I should note that the scoot absolutely jumps up to 45-50 mph indicated -- after that it creeps up to just barely 60 indicated. At lower speeds it seems like the thing should do an indicated 75 based on how it seems to pull.

xuno_g -- perhaps we could meetup sometime and you can ride my scoot -- see how it compares to yours on the bottom end -- that way I'll know if the problem is simply on the top end or if the problem is systemic.

-Dave

Specs for your bike show 74 mph top speed. Assuming that that's a real top speed, and the speedo has a 5% optimistic reading, you should be able to reach an indicated 78 mph (at sea level, I would presume). So a 75 mph indicated speed seems pretty good (more than I would have expected) at this altitude.

Three points:
1. You WILL get better speed after it's broken in (but I'm guessing probably not 15 mph better). Which brings up my second point:
2. It's under warranty. Talk to the guys at Erico. They may recommend riding it until the first service is due (600 miles?) before you mess with it. If it still seems slow, pursue the issue while it's still under warranty.
3. Probably not a good idea to keep testing the top speed until you get a few more miles on it.

hey, yea I would be willing to help you out, ride you scoot to see how it feels compared to mine and maybe you can ride mine to see how it feels compared to yours. I do agree with not trying the top speed to much durring the break in period even though according to Piaggio vespas dont really need a break in period but yea im willing to try it out and see what i think when it comes to feel and performance

Thanks Les. I agree that I should break the scoot in before testing the top speed, but according to the manual, 60 indicated is within reasonable specs during the break-in period -- given everythign I've read about the the top speed of the GT.

In any case, I'll put a few more miles on the scoot before trying again. If things don't improve I'll talk to Erico and see what they say.

-Dave