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I am assuming that there are no warning lights for battery, oil. temperature or FI on the dash when this occurs. In that case the first thing to check is for a stuck waste gate on the turbo.
Here is a parts diagram for reference: http://fiche.worldofpowersports.com/wps/showmodel.asp?Type=13&make=hondapwc&a=13&b=15&c=0&d=-TURBOCHARGER-ASSY.
You will have to cut and paste the address as it is not shown as a direct link.
To the left of the #13 there is a dashpot that controls the opening and closing of the waste gate. Follow the linkage rod to the actuating lever on the waste gate. I use a stubby 17 mm open end wrench over the end of the lever to check for free movement. It should rotate about 45 degrees with no binding in either direction. Let me know if this checks ok or not.