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New exhaust loud back fire and dies?

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So this is an old xr500 I have, been trying different exhausts with what I have available.. at one point I had dual exhaust with little pit bike mufflers, that sounded so sweet! Like an earthquake!

Anyways where i had it last I had both header pipes coming into one pipe, that shrunk down.. if your familiar with the larger xr series, they have two smaller header pipes that conjoin into one larger pipe, after mine conjoined the pipe shrunk back down to about the size of one upper header pipe, probably about an inch inner diameter, it then got much bigger and out puts to a yoshimura exhaust off of a cbr600.

With this set up it pulled very hard, would wheelie like crazy but was running decently rich as when I would rev it I'd get a nice bit of black smoke out the back

So I pulled the constrictor pipe out and replaced it with some cheap flexible exhaust stuff from AutoZone which opened up the whole exhaust to an inch and a half inner diameter, its noticeably louder, doesn't pull as hard or wheelie as easily and backfires like someone dropped TNT on the ground behind me, but the biggest problem is if I'm coasting and snap the throttle shut, and pull in the clutch, it dies, and with such a big piston if I pop the clutch it won't start, just skids my back tire, but if fires right back up fine and idles fine.. I know for the back fire and power I can go up a couple jets but I've never had something die from leaning out, I also just changed the oil, I just don't get why it keeps dieing.. should probably go back to the smaller pipe, would rather run rich then lean

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You lost back pressure by opening up the exhaust too far. The scavenging effect is a balance between valve lift, duration and timing. The XR is a pretty forgiving beast but you went too far out of parameter which is why performance as well as function suffered.

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Ya I figured I lost to much back pressure, I know with opening the exhaust I would run leaner but did I open the pipes to much? To the point where its almost like they're not even there? And the zero back pressure is what kills it when I snap the throttle close? The exhaust is essentially a glass pack, which is straight through.. the pipe constrictor I had had quite a large lip all around the inside which had to work as a sort of baffle.

straight piped with the constrictor it wasnt Terribly loud, just taking out the 10" of smaller pipe with the lip it got way louder

So I guess either get my old pipe back on cuz I know it worked or get a baffle in there

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