250cc Grandvista rev-limiter, weights and belt... (solved!)

[windwheeler]

I got my 2005 Grandvista about a week ago, has now about 10,700 miles on it.  Took it for longer trips and runs good except it "could" go faster IF there wouldn't be "something" holding it back.  At 76 mph GPS (84 indicated), about 8500 rpm it starts like bogging, stumbling. Feels to me like a rev-limiter kicks in.  IS that the case?

===============================================================================


REMARK: YES  It should not rev that high.  Main issues are worn roller weights and a worn, thus narrower belt.


================================================================================

update November 29, 2012

After changing to a new OEM Kymco belt (old one was still in specs) and experimenting with different roller and slider weights the problem went away.  Dr Pulley sliders apparently push the now even a bit wider new belt higher up on the front variator, thus giving it higher gearing, rpm dropped to somewhere between 7000-8000 rpm at top speed (can't tell with that funky step tach) and the G/V performs better than ever.  My final set-up are 18g Dr. Pulley weights.  The MYTH that lighter weights just give better acceleration and take away top end speed is with that DISPROVED.  Real life results show that clearly.

FACTS:  I tried 20g Dr. Pulley weights and they were definitely worse in performance than the OEM Kymco 20g weights!  It had NO acceleration, higher top speed though.  However, decreasing the weights to Dr. Pulley 18g sliders made all the difference, the scooter accelerates now faster AND has a higher top end at lower rpm.  This is measured on "benchmark testing" in real life on the Interstate up-hill, flat out and down hill, before and after, all GPS verified.  I have never before reached 83 mph GPS measured top speed (this is slight down-hill and with a big GIVI windshield).  And even at 83 mph the 8000 rpm square on the tach just flickered on and off, the rev-limiter never kicked in.  With the smaller stock windshield that I use in summer I am sure I can top that at least 2 more mph...

[zombie]

You can go 1gr heavier on rollers to bring the rpm down by 500. That should add approx. 3 mph. If there is a limiter on the ignition there is NO way to bypass it. It would be programed in.

[ce]

It most likely still has the 102 stock main jet., and you need more fuel at WOT.

The jet in the GV is a 2mm, which is unusual for a Keihin carb, they're usually 5mm. Since I didn't have any 2mm, I swapped out the 38 pilot jet for a 40, and added a little fuel that way, since the pilot jet is a common size.

I reached the same top speed, but it didn't bog at all.

[old geezer]

http://www.jetsrus.com/a_jet_kit_scooter/kymco_250_people.htm

[ce]

Yeah, that's the ones, thanks Geezers, it's a 3.9mm, and I must have the knock off, because the genuine isn't offered in a 102.

I'll get a 105 and a 108 to try.

In my Xciting, stock was a 98, and when I put on the Leo Vince exhaust, I finally had to put in a 115, after trying a 105 and a 110, both of which were way too lean.

[old geezer]

My People S 250 came with a .104. I have a .108 to try in it. I wish I knew what the pilot jet was. I guess I will find out when I take the carb apart.

[ce]

It's fairly easy to get in there, disconnect the air box mounting bolts and the fore and aft clamps on the carb and carefully free it to open the bowl drain to evacuate the bowl, then invert the carb and remove the 3 bolts on the fuel bowl.

I didn't disconnect any vac lines, wires or even the fuel inlet line, flipped it over and switched the jet and buttoned it back up.

Now I have to do it again when my jets get here, but I think the 40 pilot is as big as I want to go so it's not too consumptive on fuel.

[old geezer]

Yeah, I know how to do it. I just wanted to take it apart once when I replace the main jet. Now I will have to find out what size pilot jet is in there and order one and take it apart a second time.

I don't enjoy taking them apart as I once did. I guess I'm getting old. (I am).

[ce]

Well, I figured you did know how to get in one, but I just wanted to let the young bucks know how to do it in case they think it's hard.

It's only hard if your bones ache, your muscles strain, and your eyes don't work, neither with glasses or without.

[old geezer]

Well, I figured you did know how to get in one, but I just wanted to let the young bucks know how to do it in case they think it's hard.

It's only hard if your bones ache, your muscles strain, and your eyes don't work, neither with glasses or without.

My eyes don't work as good as they once did. I had cataract surgery last fall and my right eye didn't come out  as well as I would have liked. the left one came out better. Getting old ain't for sissies.

[catman2130093]

Holy crap!  Am I the only person here that thinks maybe MORE than 8500 rpm might be a tad excessive?   It's not a 2 stroke-maybe a larger engined bike would be more suitable for your use.

[zombie]

Where you been Catman?  Small world guys... Catman lives right down the street from me. We were talking scoots, the forum came up, and he punched me in the eye... Go figure!

[zombie]

Re reading this drew my attention... 1gr LIGHTER will increase rpm. Heavier will decrease rpm

[windwheeler]

After changing to a new OEM Kymco belt (old one was still in specs) and experimenting with different roller and slider weights the problem went away.  Dr Pulley sliders apparently push the now even a bit wider new belt higher up on the front variator, thus giving it higher gearing, rpm dropped to somewhere between 7000-8000 rpm at top speed (can't tell with that funky step tach) and the G/V performs better than ever.  My final set-up are 18g Dr. Pulley weights.  The MYTH (that I never supported by just thinking it through as an engineer) that lighter weights give better acceleration and take away top end speed is with that DISPROVEN. 

As a matter of fact I tried 20g Dr. Pulley weights and they were definitely worse in performance than the OEM Kymco 20g weights!  It had NO acceleration, higher top speed though.  However, decreasing the weights to Dr. Pulley 18g sliders made all the difference, the scooter accelerates now faster AND has a higher top end at lower rpm.  This is measured on "benchmark testing" in real life on the Interstate up-hill, flat out and down hill, before and after, all GPS verified.  I have never before reached 83 mph GPS measured top speed (this is slight down-hill and with a big GIVI windshield).  And even at 83 mph the 8000 rpm square on the tach just flickered on and off, the rev-limiter never kicked in.  With the smaller stock windshield that I use in summer I am sure I can top that at least 2 more mph...

[windwheeler]

Update:  the G/V still performs very well 2000 miles later, after the change, and as described above.  Fuel consumption is about the same as with the OEM slider weights, a bit worse in short distance driving and slower traffic (higher rpm at lower speed with Dr. Pulley), but better on the interstate, lower rpm with Dr. Pulley to OEM.