Just doing some top end maintenance today ( what with all this fine weather) looked up the rear cylinder exhaust port to find one side of the RC valve has come loose and eaten into the exhaust port wall. Haven't striped it down yet to get a proper look at the damage, has anyone had this happen before, was it repairable?, or is it time for a replacement cylinder.

Normaly the only damage is caused by misadjusted RC valves. When the valve is at the closed postion the valve rests on the port wall and can sometimes wear two small holes (one on each side).

If this is the sort of damage that has been caused then normaly alittle work with some fine paper in the port can remove the sharp edges where the valve has worn the port and it will be good to go again.

Make sure when you rebuild the cylinder that with the servo in the low postion the valves are just clear of touching the port wall.
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If I have to take the carbs off once more...

Don't know if it will go again its eaten about 3mm into the wall, I will take a photo on monday when I strip her down...Bad adjustment, more like no adjustment ever, the last owner was a w@n}er.

As promised here are the photos that I mentioned.

I just want to get her running again quickly, if I get the valve parts and give her a hone do you think I could get away without further repair as i'm thinking of fitting a 300 kit in the winter and want to save my money for that?

You should get away with the exhaust port wall. Its quite thick in that area. Looks like you will be needing a new power valve shaft though and I guess a set of valves. They arnt the cheapest thing new though so best you advertise for a set to keep the cost down.
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If I have to take the carbs off once more...