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Ok I have a 08 525 stock motor stock carb with powerbowl 2 and full fmf powerbomb system.The quad runs good and has pretty good throttle response but back fires everytime youcome off the throttle or decell. What are my be options to fix this as it seems to be a comon problem with these.
 

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More than likely your headpipe is leaking at the flange on the head. Pretty common on the RFS engine. You will need to trim about 1/8 inch off the front of the pipe. usually seals up after that.
 

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You still running the 170 main jet? Down a few on the main maybe?
 

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or ge tthe head pipe welded i did that works good also but the header is most likely leaking do that or cut it to fit in the flange almost 100 percent sure messed with jetting and it didnt do anything for me
 

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More than likely your headpipe is leaking at the flange on the head. Pretty common on the RFS engine. You will need to trim about 1/8 inch off the front of the pipe. usually seals up after that.

Even with the the aftermarket fmf header?
 

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maybe, do you have leakage (soot/carbon) at flange?
 

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mine is stock but grinded no black spot around header flange but still does it but way less than before pilot jet is a 45
 

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i got a 45 in mine and it does not back fire with my needle on third clip and like a 160 m.j but i got my header WELDED
 

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i got a 45 in mine and it does not back fire with my needle on third clip and like a 160 m.j but i got my header WELDED

Hey KTM RIDAA, im new here and just found this post. Im having problems with my 525xc backfiring. Do you(or anybody reading this) have any pics of where you had the pipe welded at? Besides looking for the carbon marks coming out..Any other ways to test for this leak???Also, I just got the JD jet kit. according to the kit it said to go to 180 main jet and 45 pilot for riding at sea level to 3000 ft. but 160 mj? isn't kinda low even if you are at 3-6000ft. ?
 

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Hey KTM RIDAA, im new here and just found this post. Im having problems with my 525xc backfiring. Do you(or anybody reading this) have any pics of where you had the pipe welded at? Besides looking for the carbon marks coming out..Any other ways to test for this leak???Also, I just got the JD jet kit. according to the kit it said to go to 180 main jet and 45 pilot for riding at sea level to 3000 ft. but 160 mj? isn't kinda low even if you are at 3-6000ft. ?

The head pipe gets welded to the flange that bolts on to the head. You can also trim about 1/8 in off the head pipe(s) to let it seat a little further on the flange.
 

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a 180 was way to rich for mine. the spark plug was coal black right around 160 the plug looked good and had better throttle response but yeah the head pipe slips over a flange that is bolted to the head of the motor you can get it welded to seal or cut the flange of like az said and you could test it with some sort of pressure tester put like allot of ktms have this problem backfiring on deccel so this is the fix goood luck
 

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thanks for the fast reply. well, ill carry extra jets with me when I go to the mountains to ride. Luckily I work for a steel fab shop. So, ill be able to weld it for free :)
 

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Hi all, I am having the same issue, back fire (pop) on decel as well as flame thrower, I just cut 1/8" off the front of the header tubes tonight and it didn't fix the problem. It's an 08 525xc with a KTM FMF slip on and the snorkle still installed on air box. I installed the JD jet kit with red needle and a 178 main (JD recommends 180???) and o-ring installed and 45 pilot. The quad feels real strong and starts easy. My complaint is pop and flame show. Any help you guys can offer would be appreciated.

Am I way off on jetting?

Note: I have detected a leak at the connection between the can and the head pipe, can this be the cause?

Elevation = 600ft
 

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Mine also leaks a bit at the head pipe/ can connection but I have still only very minor popping on decel and I've done nothing to the pipe at the head connection. I'd say to drop your Main jet size first to around 170 and see what that does. If you're throwing flames, it's because you've got too much fuel. Also, make sure to adjust your fuel screw properly. A well tuned carb can help reduce the popping on decel as I've found out. Might need a bit more fuel at idle to 1/4 throttle position.
For reference, I'm running stock exhaust with intake mods, a 162 mj, 42 pj, with fuel screw at 2.75 turns out. Elevation 1200ft- Runs far better than with the 162 than the 170 mj
Cheers!
 

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Mine also leaks a bit at the head pipe/ can connection but I have still only very minor popping on decel and I've done nothing to the pipe at the head connection. I'd say to drop your Main jet size first to around 170 and see what that does. If you're throwing flames, it's because you've got too much fuel. Also, make sure to adjust your fuel screw properly. A well tuned carb can help reduce the popping on decel as I've found out. Might need a bit more fuel at idle to 1/4 throttle position.
For reference, I'm running stock exhaust with intake mods, a 162 mj, 42 pj, with fuel screw at 2.75 turns out. Elevation 1200ft- Runs far better than with the 162 than the 170 mj
Cheers!


What exactly is the intake mod? I've heard of it before. Just not sure what you guys are modding though. I'll take the 162 jet with me when I got to the mountains just incase the JD sheet is way off.
 

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More than likely your headpipe is leaking at the flange on the head. Pretty common on the RFS engine. You will need to trim about 1/8 inch off the front of the pipe. usually seals up after that.
is it normal for the pipe to be stuck on super hard on the head of the engine?
 

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More than likely your headpipe is leaking at the flange on the head. Pretty common on the RFS engine. You will need to trim about 1/8 inch off the front of the pipe. usually seals up after that.
ive tried to take it off but its stuck on too much so im guessing that the pipe isnt the problem?
 
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