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Discussion Starter · #1 ·
Just bought an 09 525 xc. Bought it from a dealer that the original owner traded in. Quads super clean. I didnt get to test drive it cause were getting hammered with rain here but it started and idled fine. I went to go riding yesterday and it started and idles perfect like it did at the dealer. I went to give it some gas to stsrt riding and it started spitting, sputtering and then backfiring. I revved it up into the high rpm and it clears up but pops and backfires on decel. I took the carb apart and cleaned everything. It wasn't very dirty to begin with but I figured I'd check. Put it back together and it still does it. Any clues?? Its got a fmf slip on. Jetting was 178 main, 62 pilot and 85 leak. Dealer said he rode it the day the previous owner traded it in and it ran great. I dont really believe dealers but im out of ideas. A lot easier to work on my banshee lol. Any advice would be great. Thanks!
 

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That is a really big pilot. Should be a 42 stock if I remember correctly. A 45 pilot will help mask some decel popping these were famous for, but isn't really needed with a proper fitting exhaust and some carb tuning. Check the fit between the pipe sections and apply some high temp RTV if loose. Also slide the head pipe forward and see if the pipe is hitting the welds on the flange that is bolted to the head. This was common and wouldn't let the pipe seal up to the flange on the inside like it's supposed to. Then they suck air right at the head and pop on decel. Fix for this is grind 1/8" or so off the front of the head pipes (not the flange) so the pipes don't hit the welds. Might have to pull the rear shock off to get the head pipe out for this.

If it has a leak jet in the float bowl it has been modified as KTMs were never tapped for a jet, just had a bleed hole. This is a popular mod though. I would go back to a 42 or 45 pilot and a 55 leak. That big 62 pilot is going to over fuel on the bottom when it starts to rev and bog. The big 85 leak is not going to send enough fuel through the accelerator pump circuit right when you stab the throttle. So you're going to go from not enough fuel to too much right off idle. Whoever setup the jetting was probably trying to mask one problem with another.

If that's all in order check the boot between the head and carb for cracks. These were notorious for cracking as they got some age on them. They crack from the inside out and the clamps can hide it so you almost have to take them off the quad and inspect from the inside.
 

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Discussion Starter · #3 ·
That is a really big pilot. Should be a 42 stock if I remember correctly. A 45 pilot will help mask some decel popping these were famous for, but isn't really needed with a proper fitting exhaust and some carb tuning. Check the fit between the pipe sections and apply some high temp RTV if loose. Also slide the head pipe forward and see if the pipe is hitting the welds on the flange that is bolted to the head. This was common and wouldn't let the pipe seal up to the flange on the inside like it's supposed to. Then they suck air right at the head and pop on decel. Fix for this is grind 1/8" or so off the front of the head pipes (not the flange) so the pipes don't hit the welds. Might have to pull the rear shock off to get the head pipe out for this.

If it has a leak jet in the float bowl it has been modified as KTMs were never tapped for a jet, just had a bleed hole. This is a popular mod though. I would go back to a 42 or 45 pilot and a 55 leak. That big 62 pilot is going to over fuel on the bottom when it starts to rev and bog. The big 85 leak is not going to send enough fuel through the accelerator pump circuit right when you stab the throttle. So you're going to go from not enough fuel to too much right off idle. Whoever setup the jetting was probably trying to mask one problem with another.

If that's all in order check the boot between the head and carb for cracks. These were notorious for cracking as they got some age on them. They crack from the inside out and the clamps can hide it so you almost have to take them off the quad and inspect from the inside.
Sorry I should have proofread the post lol. It does has a 42 pilot and 55 leak. Thats a typo. But I spent a little more time riding it yesterday. Cleaned carb again and flushed tank and filled with fresh gas. The hesitation isn't as bad as it was before. Still starts right up and idles perfect. Runs fine full throttle. But mid range has a little hesitation and backfire on decel. I checked the flange at the head pipe and its sealed tight. I sprayed starting fluid all around the I take boot while it was running and no change in rpm. If thats the stock pilot jet you think im gonna need to go up a size since it has a fmf slip on? I've always jet up for mods but this came the way it is already. Also I pulled the choke out while it was running and it doesn't really effect idle or wide open but masks the hesitation more. Thinking im gonna take it to a shop and have them go through it and jet accordingly since I have no time with work.
 

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I'm running a pipe and other mods and I think I'm running the 42 pilot, but it's been a while since I've been in there. The FCR carbs are pretty sensitive to the needle setting. If the choke helped in the mid range I'd pick the needle up one spot and try it (move the needle clip down 1 slot).
 

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Discussion Starter · #5 ·
I'm running a pipe and other mods and I think I'm running the 42 pilot, but it's been a while since I've been in there. The FCR carbs are pretty sensitive to the needle setting. If the choke helped in the mid range I'd pick the needle up one spot and try it (move the needle clip down 1 slot).
Ok ill give that a shot. Im unsure of what needles in it I didnt check. Ill tear it apart next week after work.
 
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