How long can I run open pipes on stock jetting before causing damage

[Byard]

I'm very confused. Why would running open pipes damage valves? 

[mysterious_rider]

I don't know what you're talking about, the slash cut pipe is looking fine to me. 

[Manaenrc]

I'm very confused. Why would running open pipes damage valves? 

Because when you open the exhaust it leans out the mixture. A lean mixture will cause excessive heat in the combustion chamber. This heat is especially bad around the exhaust valves. the first thing you will see is your valve clearance and valve seal problems. Eventually you will burn the exhaust valves up.
How do you know if you're running too lean? Simple check your plugs, pure white is bad (too lean), white on one side (a little lean), even gray possibly with a red tint (perfect), black (too rich).



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[Kijona]

I'm very confused. Why would running open pipes damage valves? 

Because when you open the exhaust it leans out the mixture. A lean mixture will cause excessive heat in the combustion chamber. This heat is especially bad around the exhaust valves. the first thing you will see is your valve clearance and valve seal problems. Eventually you will burn the exhaust valves up.
How do you know if you're running too lean? Simple check your plugs, pure white is bad (too lean), white on one side (a little lean), even gray possibly with a red tint (perfect), black (too rich).

To expound on what you said...

The effect backpressure has on engine mixture is far less profound on 4-stroke motors versus 2-stroke but it's still there. The shorter the pipe is, the less backpressure there is. Being knocked off right there at the muffler isn't really a huge problem but it will be way, way down the line.

If the pipes are short enough, they can pull cool air back in and warp the valves (due to being constantly heated and cooled).

[termlifed]

Thanks to Kijona and everyone who offered advice and suggestions, its good to hear that I most likely haven't done any damage. Im picking up an exhaust from a gstwin member tomorrow so I wont have to fix this one. Anyone interested in a custom gs500 straight racing pipe?

I don't know what you're talking about, the slash cut pipe is looking fine to me. 

To be honest I like the slash cut look too but hate the sound, too chopper like. If it were an I4, however, I might have had to run with it for a little while longer

[Kijona]

Thanks to Kijona and everyone who offered advice and suggestions, its good to hear that I most likely haven't done any damage. Im picking up an exhaust from a gstwin member tomorrow so I wont have to fix this one. Anyone interested in a custom gs500 straight racing pipe?

I don't know what you're talking about, the slash cut pipe is looking fine to me. 

To be honest I like the slash cut look too but hate the sound, too chopper like. If it were an I4, however, I might have had to run with it for a little while longer

No problem man. You might offer it up on the FS/FT area. If it's in good shape without any rust or anything it will probably get snatched up quick - lots of people have rusty headers.