ignition retard
Member
- Dec 8, 2007
- 138
- 0
My powervalve is intermittently sticking open.
I put a re plated cylinder on, and as soon as I gave it full throttle during break-in the powervalve stuck open. I disassembled the top end cleaned and checked the powervalve, everything seemed ok, so I ran the bike some more, same result, the powervalve would stick open when the rpm advanced using more than ½ throttle. I learned I could unstick it by going faster in higher gears then bring the rpm up by downshifting with the throttle off.
I took the pipe and powervalve cover off and actuated it by hand. It would stick about ¾ the way open about one out of six times I moved it through its operating range. I reached up into the exhaust port and found that by pressing the inside of the right powervalve piston side face I could get it to stick every time. If I pressed the outside it wouldn't stick. I determined that uneven exhaust gas pressure on the face of the powervalve during movement was side loading it in its bore, causing it to stick.
I disassembled the top end cleaned and closely inspected the powervalve sliders. I found that some of the material had been “pushed around” and that some sharp protrusions had formed on the piston side faces, I then performed a very light deburring procedure to remove them.
This drastically improved its operation, however, it will still sometimes stick during serious riding. If I just cruise, it doesn't stick.
These valves worked in the cylinder I took off, and they used to work just fine in the cylinder I had replated. Could the replating company have switched cylinders? Do powervalves need occasional replacement? Could the powervalve bores be worn out?
I put a re plated cylinder on, and as soon as I gave it full throttle during break-in the powervalve stuck open. I disassembled the top end cleaned and checked the powervalve, everything seemed ok, so I ran the bike some more, same result, the powervalve would stick open when the rpm advanced using more than ½ throttle. I learned I could unstick it by going faster in higher gears then bring the rpm up by downshifting with the throttle off.
I took the pipe and powervalve cover off and actuated it by hand. It would stick about ¾ the way open about one out of six times I moved it through its operating range. I reached up into the exhaust port and found that by pressing the inside of the right powervalve piston side face I could get it to stick every time. If I pressed the outside it wouldn't stick. I determined that uneven exhaust gas pressure on the face of the powervalve during movement was side loading it in its bore, causing it to stick.
I disassembled the top end cleaned and closely inspected the powervalve sliders. I found that some of the material had been “pushed around” and that some sharp protrusions had formed on the piston side faces, I then performed a very light deburring procedure to remove them.
This drastically improved its operation, however, it will still sometimes stick during serious riding. If I just cruise, it doesn't stick.
These valves worked in the cylinder I took off, and they used to work just fine in the cylinder I had replated. Could the replating company have switched cylinders? Do powervalves need occasional replacement? Could the powervalve bores be worn out?
