Hello all! I've been lurking this place since I bought my '97 GS500. It's an incredible resource. props on the huge amount of knowledge on this board.

I was hoping someone could help me out a bit with a problem I've been having. I recently bought a '97 gs500 and have been noticing a couple loud
pops from the exhaust when the engine comes down from mid to high rpms. I'm the third owner of the bike and whoever was the first owner did
some mods. There's a vance & hines slip on exhaust on the bike, so I investigated a little further and found that the first owner also put in a K&N air
filter in as well. My guess is that the owner didn't rejet the carbs after adding these mods because the guy I bought it from said the bike has always
backfired like that. Anyway, I was hoping to get an idea of where to start before I blindly went ripping into the bike. Any suggestions are appreciated!

Some backfiring is normal with a higher flow exhaust & filter. It has to do with excess gas getting sucked through before the carbs have a chance to close, then it ignites in the exhaust.

Here is more detailed info:
http://www.mikuni.com/tg_backfires_in_exhaust.html

Actually all bikes backfires a little but the stock exhaust muffles it.

thanks, that helped a lot. seems like the only fix for this is to rejet the pilot? do most people here with aftermarket exhausts just let it backfire or is there a standard way of fixing this?

I just let it pop. You can increase the pilot jet 1 size and see if it reduces.

V&H + K&N = 37 idle and 150 main, unless the 'slipon ' is different from a 'full' V&H.

I have 2 #4 stainless washers on the needles, and 3 1/4 or so turns out on the mixture screws. It warms up quickly, idles smoothly, and accelerates smoothly. Tomorrow it will all go to shaZam! for no reason now but that's normal for me.

Plug chops are the best way of finding stuff out I've found, besides just plain sniffing the exhaust and coming back with a snoot full of gas.