250 Grandvista top speed issue

[tonyode]

Hello all. New scooter own here. Bought a used 2009 Grandvista 250. It needed a lil work. But it started right up. To date, I have replaced the belt as well as new rollers and plate. I did this as I could only get my top speed to about 45-50. The scooter accelerates to 40-45 just fine. But doesn't seem to want to go much further. Even after replacing the belt and rollers. I have ran carb clean and can of seafoam through it as well. The engine seems to idle and run smooth. Just am not getting much top end speed out. I have read where it should do at least 70-75.
Any other tips I should try? Any advice would be appreciated!
Thanks!

[scuba1065]

check engine compression. Lot's of opinions on this forum. enjoy the feedback. It's good to have toys.

[windwheeler]

Seem like something seriously wrong.  A good running Grand Vista should zip up to 90 mph indicated (80 mph true GPS), and 45-50 mph indicated  is just a bit past idle throttle position  ;- )

OK: let's start with two basics:
-- yes, check compression; the previous owner may have run it with low oil level and scared the cylinder   
-- On the center stand testing, full throttle (be careful with this test NOT to touch the ground with the rear wheel), can you get 8000-9000 rpm until the rev-limiter kicks in?  Even with bad compression this should be possible; if not your ignition/rev limiter may be faulty, or your carburetor may have issues

Let us know.

[mrbios]

Hello all. New scooter own here. Bought a used 2009 Grandvista 250.....

I routinely do 77 mph (82 indicated) on my 2005 GV250.  How many miles does this scoot have on it?  What did the previous owner tell you?  Did you download the service manual yet? 

If this is a drive line issue (belt/clutch slipping) I would expect discolored metal and a burning smell.  I supose the variator might not be reaching the gear ratio to go over 50mph but I suspect the carb is still the issue or a vacuum leak.  If the carb is not delivering fuel when you use full throttle you should feel the motor cutting out.

How many seconds from standstill does it take to reach 50mph? 

Can you reach 50mph easily?

Does the throttle open all the way?  Maybe the throttle cable is not opening the carb all the way. 

A compression test is a good idea but I doubt the motor is worn out.  Anyone done this on a GV250 or other kymco 250cc motor for him to compare numbers against?

[richard1958]

I'm new to this forum but not to working on my own bikes.  Remember, when you check the compression to have the throttle full on.  Also the grandvista 250 manual gives a spec:  Compression: 15±2kg/cm_.  Unfortunately I don't off hand know how to convert this spec to say pounds per square inch.  If the reading is low, then squirt oil into the cylinder through the spark plug hole and try again.  If the compression goes up then it's probably the rings or cylinder wall.  If not then it might be a bad valve.

In addition maybe someone knows this offhand but I'll have to run an experiment and see what my RPM's are at 45 mph.  THis might tell us if the transmission is not providing a high enough gear ratio.  It used to bug me when I was a kid that my Harley Topper which was a scooter with a similar belt transmission to the present day "twist and go" scooters, that I could only go 45 mph probably because the gear ratio wasn't higher.  My friends on vespas and lambrettas would finally pass me by as they could do 50 plus.

Hope this helps.

[windwheeler]

FYI mrbios:  Forgetting to check the oil level (as soo many people do nowadays, because they think oil consumption is a thing of the past, will be resulting in scaring the cylinder walls and a low compression, thus low power and top speed.  Now with only 50 mph Mr. tonyode needs to get back with us and give us a bit more feedback, as there can be many other things wrong.

I routinely do 77 mph (82 indicated) on my 2005 GV250.  How many miles does this scoot have on it?  What did the previous owner tell you?  Did you download the service manual yet? 

If this is a drive line issue (belt/clutch slipping) I would expect discolored metal and a burning smell.  I supose the variator might not be reaching the gear ratio to go over 50mph but I suspect the carb is still the issue or a vacuum leak.  If the carb is not delivering fuel when you use full throttle you should feel the motor cutting out.

How many seconds from standstill does it take to reach 50mph? 

Can you reach 50mph easily?

Does the throttle open all the way?  Maybe the throttle cable is not opening the carb all the way. 

A compression test is a good idea but I doubt the motor is worn out.  Anyone done this on a GV250 or other kymco 250cc motor for him to compare numbers against?

[tonyode]

Ok, let me start with that I bought this scooter at an auction so I didn't get to talk to previous owner. The scooter only has 3000K miles on it. It accelerates pretty good, pops up to 40-45 pretty quick. But struggles to hit 50-55mph on my digital speedometer.
On stand, with rear wheel up air, the most RPM I can get is 5-6K.
Things I have done:
1. Replace drive belt
2. new rollers(standard) and variator plate (rollers sit in)
3. Sprayed carb with seafoam.
4. Ran seafoam through gas with new gas.
5. New spark plug.

As I said, it seems to run smooth, no sputtering, cutting out or rough running at all. I am somewhat mechanically inclined and I can't believe there is compression issue based on how it is running. I don't believe oil was low when I got it home.

When I bought it, it was pretty sitting for a pretty good time period. But since then I have ran it pretty good, at least couple tanks of gas thru.

Thoughts?
Carb?
Valves?

[windwheeler]

Let me through a few things out:

Running out of power without big sputter is usually a lean condition.  5-6000 rpm on center stand is showing some sorf of restriction.  However a few thoughts in all directions:

- main jet* carburetor clogged (*comes in at 3-4000 rpm, then responsible for top rpm)
- major vacuum leak intake
- intake/air filter clogged (mouse nest; I just had that on a motorcyle; did also not want to run on top)

I still would recommend the compression check.  Just that it had enough oil in the engine edoesn't mean ANYTHING. Anybody can add oil to sell.  Facts talk on the compression check, if it is good, you can 100% move on to other and have peace of mind.

[jackgermain]

ADJUST THE VALVES !!

[windwheeler]

I would rather say "check valves" and bet there is no way it could be that far off to cause the loss of top speed.  I think he said  this G/V has only 3-4000 miles, can't be that bad out of spec, unless somebody did an "early bad job".

[richard1958]

I ran my grandvista 250 which is a 2009 model at 45 on a level road and it held at 4000 rpm.  I did the same at 50 and it was up to 5000 rpm.  Of course the granularity is 1000 rpm, but that should give you an idea of what to expect at those two speeds.

[ophelia]

I think you have some very good tips. Clean the main jet and make sure you can see through it with a flashlight.

Pump the tires up too. I like 28/28 psi cold, but follow the manual.

[tonyode]

Ok gentleman, thanks for all the input. I think I have narrowed it down to a possible vacuum issue. I cleaned the carb thoroughly. It doesn't start or run as smooth as it did. Not sure what I did. I didn't take the carb apart, just sprayed the hell out of it with seafoam.

Then I noticed a hose that looks like it had been cut off that comes off the side of the carb, off top. I have posted a pic. When I would plug hoses, I could get the engine to rev up to 8-9K. Much higher RPM than previously.

I also noticed a hose that comes out of what I think is some kind of diaphragm possibly. The hose looks to have been cut off as well. Is there an area I can go to get some kind of schematic for the vacuum hoses?
Here at two pics. Any help would be greatly appreciated.

[tonyode]

Oops, here is pic 1.

[tonyode]

Pic of house out of carb.

BTW, I put screws in each end of hose so to be able to identify.