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Stupid ? About Backfire On De-acceleration

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OK folks, I'm sure this question has been asked a million times but here we go again. I put a new Big Gun exhaust system on and now the bike (05 WR 450) backfires like mad on de-acceleration. Big Gun told me no jetting changes were needed with their exhaust. I've messed with the fuel screw but the jetting I left at 168 main and a 48 pilot(?). Should I be running a bigger pilot jet, or main? :)

It ran perfect with the baffle taken outta the stock pipe and I'm running the stock needle sa it came from the factory

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OK folks, I'm sure this question has been asked a million times but here we go again. I put a new Big Gun exhaust system on and now the bike (05 WR 450) backfires like mad on de-acceleration. Big Gun told me no jetting changes were needed with their exhaust. I've messed with the fuel screw but the jetting I left at 168 main and a 48 pilot(?). Should I be running a bigger pilot jet, or main? :)

It ran perfect with the baffle taken outta the stock pipe and I'm running the stock needle sa it came from the factory

Exhaust manufacturers commonly say that rejetting is not required, but that's NOT the same as saying a rejet is not needed. All it means is that installing the pipe will not lean out the mixture enough to cause engine damage in most cases. To get maximum performance out of an exhaust change, rejetting is a must. The recommendation that it isn't necessary is more a marketing tool than a fact. When I installed the GYT-R insert and did the free mods I experienced the same problems you describe. After I rejetted the bike I not only eliminated them, but found way more power than I expected. Should I go to an aftermarket exhaust, I expect I will again have to rejet.

Does this mean I can't have your stock exhaust anymore? :) I'm going to Race Tech tomorrow and was going to swing by your house on the way home. Are you anywhere close to Corona?

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When I installed my Big Gun exhaust on my YZ250F, I changed my pilot, needle one clip, and main to a richer setting. I was getting the slight popping on deceleration as well before re-jetting. Sorry, I don't have any WR related info, as my bike is popping too on deceleration now due to the AIS. At least, I hope that is what is causing it. What altitude do you ride?

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OK folks, I'm sure this question has been asked a million times but here we go again. I put a new Big Gun exhaust system on and now the bike (05 WR 450) backfires like mad on de-acceleration. Big Gun told me no jetting changes were needed with their exhaust. I've messed with the fuel screw but the jetting I left at 168 main and a 48 pilot(?). Should I be running a bigger pilot jet, or main? :)

It ran perfect with the baffle taken outta the stock pipe and I'm running the stock needle sa it came from the factory

You have just put a pipe on to expose the backfiring. It was doing it before you just couldn't hear it. I put the E2 on mine and it backfires like mad with a rejet. A 48 pilot is ok and so is the 168 main. I currently have a 175 main(too much) and will change it back to 168 or 170. Have you taken off your AIS system yet. :) That is a big culprit to the backfiring :p

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RadRick- I don't live too far from Corona, that is, if you leave your house at the right time, hop on the 241 toll road, and haul ass back to Corona before the 91 backs up :) I've got a bunch of stuff to do after work tomorrow than I'm heading out to the Blythe area to do some riding over the holiday. I probably wouldn't be able to hook up with ya til next week. Sorry

Motodude42- My elevation varies where I ride at. At home it's about 600 feet above sea level, but the race i did last weekend(or attempted to do) is probably 3500 feet above sea level. I think the low desert area I ride in is somewhere from 1000 to 2000 feet above sea level

DesertWR- I haven't taken off the AIS just yet. I need to order one from LoweDog but keep putting it off. With the stock pipe I could hear very slight backfiring, but the Big Gun shoots flames, literally!!!!!! :) I still haven't broken the Big Gun just yet

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[DesertWR- I haven't taken off the AIS just yet. I need to order one from LoweDog but keep putting it off. With the stock pipe I could hear very slight backfiring, but the Big Gun shoots flames, literally!!!!!! :) I still haven't broken the Big Gun just yet

Thats why they call it the Big Gun :):p:D:D

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