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