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Vespa GT 200
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Location: Loughborough
 
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Vespa GT 200
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Location: Loughborough
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Good evening Vesparistas from here in the UK.

My 2003 Vespa GT200 is lacking top end speed. It starts and runs but will only manage around 62mph. It now has 12000Km on the clock and has a genuine belt and rollers fitted to it. I have owned the bike for two years and it has always been this slow since 3000Km. Do these scooters need the ecu to be reset when a new battery is fitted as a new battery was fitted by the previous owner just before I bought the scooter? Thanking you in advance for any advice.
Kind regards Paul
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The Hornet (GT200, aka Love Bug) and 'Dimples' - a GTS 300
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@jimc avatar
The Hornet (GT200, aka Love Bug) and 'Dimples' - a GTS 300
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Yep, that's 10mph slow. It should be able to do 70-75 (GPS), 80-85 indicated (hugely over-optimistic).
@znomit avatar
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Veni, Vidi, Posti
LX190 Friday afternoon special, [s]Primavera[/s], S50, too many pushbikes
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@znomit avatar
LX190 Friday afternoon special, [s]Primavera[/s], S50, too many pushbikes
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Is that GPS verified speed?
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Veni, Vidi, Posti
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Location: Tega Cay, SC
 
Veni, Vidi, Posti
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If the carb has not been rebuilt, I would suggest you take a look at the diaphragm. Even a very small hole will keep it from working right and getting up to top speed.
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Molto Verboso
S150 '09, Beo 500ie '08
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Molto Verboso
@juan_orhea avatar
S150 '09, Beo 500ie '08
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Tierney wrote:
If the carb has not been rebuilt, I would suggest you take a look at the diaphragm. Even a very small hole will keep it from working right and getting up to top speed.
Agree - having briefly dealt with this on my 150 I can confirm that that diaphragm is easy to overlook when troubleshooting, difficult to spot when imperfectly sealed (or poked/torn), and capable of just slightly affecting performance. I fixed mine by disassembling that "opposite" side of the carb, coating both sides of the diaphragm with a very light coat of silicone grease, and very carefully reassembling it. I don't know if the grease or the careful reassembly fixed the problem but it was immediately, noticeably, fixed.
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Molto Verboso
GTS 300ie
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Location: Sunshine Coast, Australia
 
Molto Verboso
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GTS 300ie
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Maybe it's a GT125 masquerading.....
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Enthusiast
2005 Vespa GT200
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Posts: 94
Location: San clemente ca
 
Enthusiast
2005 Vespa GT200
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Location: San clemente ca
UTC quote
There is no ecu
@chachi13 avatar
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2022 Primavera 150
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@chachi13 avatar
2022 Primavera 150
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Nitro200 wrote:
There is no ecu
huh?
Forum member supplied image with no explanatory text
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Molto Verboso
Piaggio Beverly 300 ie - 2012
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Molto Verboso
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Piaggio Beverly 300 ie - 2012
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UTC quote
Sorrelite wrote:
Good evening Vesparistas from here in the UK.

My 2003 Vespa GT200 is lacking top end speed. It starts and runs but will only manage around 62mph. It now has 12000Km on the clock and has a genuine belt and rollers fitted to it. I have owned the bike for two years and it has always been this slow since 3000Km. Do these scooters need the ecu to be reset when a new battery is fitted as a new battery was fitted by the previous owner just before I bought the scooter? Thanking you in advance for any advice.
Kind regards Paul
So you have it for 2 years and back then, when you bought it, it had 3000km on the odo and also did max around 62mph.
Is that correct understanding?

You say it is fitted with a genuine belt and rollers. Did you fit or had fitted these?

I never heard of a need to reset an ECU when you fit a new battery.
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Enthusiast
2005 Vespa GT200
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Location: San clemente ca
 
Enthusiast
2005 Vespa GT200
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Location: San clemente ca
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Ecu cdi I'm sure there's a reason they r called two different things.
OP
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Member
Vespa GT 200
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Location: Loughborough
 
Member
Vespa GT 200
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Location: Loughborough
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Thank you all for your thoughts so far. The bike has always run like this since I bought it. I cleaned the carb out when I bought it as it had been off the road for a year, but all seemed well with the diaphragm. I will take it out this weekend and have another look - so thanks for that suggestion.
I do all my own servicing and repairs to all my vehicles so it was me who fitted the belt and rollers with all genuine Piaggio parts. I checked them only last week and all is well. The variator surfaces are good with no signs of grooving.
I rode another GT200 within our club and it was good for 70-75mph!! Mine accelerates just as quick but fails to reach low sixties!! I am going to adjust the valve clearances in the not to distant future but wanted to try and sort this problem out beforehand. I have checked the engine number and it is a 198cc as per the logbook. I asked you all about the ecu as the previous/only owner told me he only rode it slowly around town so, I wondered if the ecu had "learnt" a false top speed as some car ecu's have this ability apparently.
Please keep the suggestions coming and I will keep you all informed of my findings.
Thank you fellow Vesparistas
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Veni, Vidi, Posti
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Location: Tega Cay, SC
 
Veni, Vidi, Posti
Joined: UTC
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Location: Tega Cay, SC
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The diaphragm is easy enough to remove on the scoot - 4 screws to remove the top and release the tension on the spring slowly. When you check the rubber part itself, get a strong flashlight behind it and get in there with your fingers to stretch it out a bit along the crease. Check the slide for wear and small cracks. You got this, good luck.
@wleuthold avatar
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Veni, Vidi, Posti
2006 Vespa GT (Rocket): 2007 Vespa GT (Vanessa): 2009 Yamaha Zuma 125: 2018 Yamaha Xmax (Big Ugly), 2023 Vespa GTS300 (Ghost)
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2006 Vespa GT (Rocket): 2007 Vespa GT (Vanessa): 2009 Yamaha Zuma 125: 2018 Yamaha Xmax (Big Ugly), 2023 Vespa GTS300 (Ghost)
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UTC quote
Does it run smoothly at its low top speed, or is it stumbling?

If smooth running all of the time, and with it having power to accelerate, I think it might be gearing.

Roller weights come to mind, possibly too light.

Also check the washer between the plates on the variator.

That should be very thin.

A thick one will prevent the belt from getting to the top of the pulleys.

Bill
@jimc avatar
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The Hornet (GT200, aka Love Bug) and 'Dimples' - a GTS 300
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@jimc avatar
The Hornet (GT200, aka Love Bug) and 'Dimples' - a GTS 300
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Location: Pleasant Hill, CA
UTC quote
What rollers did you install? Too light and it'll hit the rev limiter well before the nominal top speed.
OP
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Member
Vespa GT 200
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Posts: 9
Location: Loughborough
 
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Vespa GT 200
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Location: Loughborough
UTC quote
Good evening from the UK.
I have fixed the low top end speed issue!! It was the diaphragm not seating in the carb body properly, thus not opening the slide fully. Thank you to Tierney and Rich O'Shea for directing me to the problem. Indeed, thank you all for taking the time to offer your thoughts. I took the GT out last night and got 80mph indicated which is probably around 72mph ish and there was still a bit left but I didn't push it any further. All round acceleration is improved also. Once again, thank you fellow Vesparistas.
@jimc avatar
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The Hornet (GT200, aka Love Bug) and 'Dimples' - a GTS 300
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Location: Pleasant Hill, CA
 
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@jimc avatar
The Hornet (GT200, aka Love Bug) and 'Dimples' - a GTS 300
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Thanks for reporting back.

Editing the thread title to include 'Solved'.
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Veni, Vidi, Posti
GTS 300ABS, Buddy 125, Buddy Kick 125
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Location: Oregon City, OR
 
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@dooglas avatar
GTS 300ABS, Buddy 125, Buddy Kick 125
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Location: Oregon City, OR
UTC quote
Nitro200 wrote:
Ecu cdi I'm sure there's a reason they r called two different things.
Technically speaking, I believe that a CDI is a type of ECU. In the case of modern Vespas, CDI is usually a term for electronic control units which control ignition timing while ECU is a more general term referring to a unit which controls both ignition timing and fuel injection. There are a lot of different ECU's in this world.
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Veni, Vidi, Posti
Joined: UTC
Posts: 7093
Location: Tega Cay, SC
 
Veni, Vidi, Posti
Joined: UTC
Posts: 7093
Location: Tega Cay, SC
UTC quote
Sorrelite wrote:
Good evening from the UK.
I have fixed the low top end speed issue!! It was the diaphragm not seating in the carb body properly, thus not opening the slide fully. Thank you to Tierney and Rich O'Shea for directing me to the problem. Indeed, thank you all for taking the time to offer your thoughts. I took the GT out last night and got 80mph indicated which is probably around 72mph ish and there was still a bit left but I didn't push it any further. All round acceleration is improved also. Once again, thank you fellow Vesparistas.
Glad you got it sorted. This is a real easy mistake to make. I usually use a bit of grease to seat the diaphragm lip in the groove at the top of the carb body before installing the cover and it seems to work.
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