Can you explain why/where to look when a Xingyue Xy260T-4 loses top speed?

by RCW
(Platte City, MO, USA)

I have a 2008 Xingyue XY260T-4 with 4300 miles. It ran 70 mph when new, then one day dropped top speed to 55 mph @5200rpm and 40-45 mph top speed going uphill. Variator roller weights showed flat spots, so I replaced them first with 13 grams, then 15 grams, but changed back to 10 grams as they worked best.

I also have changed the spark plug, new vacuum & fuel lines, new fuel pump, cleaned carb., checked for intake leaks, valve adjustment, checked timing, checked full open throttle of carb.,
checked choke, checked CDI, checked exhaust system. Cannot find anything that should cause power loss.

Engine starts good, runs smooth. Excellent running at 55 mph on flat, but won't run over
40-45 uphill. Need the speed back to drive on highway. Can you recommend any place else to look
to recover the power loss?

Comments for Can you explain why/where to look when a Xingyue Xy260T-4 loses top speed?

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Oct 12, 2010
Xingyue Xy260T-4 loses top speed...FIXED!
by: RCW

Got it FIXED! "Nails" posted his problem for losing top speed. It was the "diaphram" in the carb.....the plastic that snaps together in the center of the diaphram loosens in time and allows air to flow to top of diaphram and not raise the needle as high as it should. Inserted Ultra Blue Silcone gasket seal around top outside edge of the plastic center piece. Top speed is back....climbs hills as it should once again. Now is running 7000rpm under load. I don't run top end but hubby said he had it up to 75mph! Thank you, Nails!!!!!

Oct 11, 2010
Xingyue Xy260T-4 comment back to Jim
by: RCW

Yes, fuel pump replaced. Checked the spark plug again. It checks out perfectly in color. We went to the Scooterdoc.proboard as you suggested and found a manual with specifications listed. Thank you. The spark plug cap resistance is high according to specs. Will try to find a replacement. Still unable to pin point the problem. Getting ready to check the diaphram starts right up and doesn't miss a beat up to the 5400rmp @ 50-55mph. Keep suggestions coming......thanks!

Oct 04, 2010
by: Jim Zeiser

Go to and ask there. JRRyan has extensive experience with the Linhai Yamaha 250 and can help you with your troubles. Did you replace the fuel pump? It still sounds like some kind of vacuum/fuel delivery problem to me.

Oct 03, 2010
Intake manifold
by: Jim Zeiser

I would start looking at vacuum lines and for cracks in the intake manifold. Also check and see if the carburetor diaphragm is all right. A simple (or not) plug check will tell you a lot.

Take the scooter out on a flat road, run wide open for a minute then hit the kill switch and pull over. Check and see what color the spark plug is. If it's white it's running too lean, if black or some dark color, too rich.

Sep 28, 2010
by: RCW

In response to Jim, that was one of the first things we tried. New belt, like all the other guesses, did not make any difference. Clutch & rear pulley doesn't slip and comes on up to high gear.

The original roller weighs were 12grams. The "beast" will turn out 8500 rpm on the maintenance stand but only 5200 rpm under load. Clutch doesn't slip. Speed is no different with two or one persons. Any other suggestions? Thanks!


Sep 27, 2010
by: JIm Zeiser

You didn't say how heavy your original rollers were but I'm guessing they were heavier than 15 grams. Also I would get a new belt and see if that helps. When you put it on rough up the face of the variator with a mild sand paper to make sure it doesn't slip.

Then before you put the outer cover on, start the scooter on the center stand and make sure the belt goes up to the top of your variator so you know that you're getting full gearing and top speed.

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