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Discussion Starter · #1 ·
I have a 2002 Raptor 660, with a Yoshi Pipe, and Header. Intake is an UM Racing aluminum airbox no lid with a K&N Airfilter with an outerware(prefilter), nothing has been done to the motor.

I'm at 4300 feet above sea level.
GYTR Neddles 3rd clip
Pilots 25
Mains 155/160
Fuel Screws 3L/3R

Problem. Backfires like crazy on decel, But also way to rich from idle to 1/4 throttle. ?????? how can it be to rich, and still backfire like crazy on decel? When in netural and reving it up, I see a puff of black smoke here and there, Wide open still fills like I need to go up 1 size on the Jets to 160/165.

It runs like a champ from 1/4 to 3/4.
Any Idea.
 

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I run the vitos kit, I am at 3200'. Same mains, CT Pipe, open airbox, foam filter. I run the 25 pilots, and my screws are out around 2.25. Any more than that and it starts getting too rich.

I know it backfires on decel, but just try setting your screws in some and see if that helps or makes it worse.
 

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I have a 2002 Raptor 660, with a Yoshi Pipe, and Header. Intake is an UM Racing aluminum airbox no lid with a K&N Airfilter with an outerware(prefilter), nothing has been done to the motor.

I'm at 4300 feet above sea level.
GYTR Neddles 3rd clip
Pilots 25
Mains 155/160
Fuel Screws 3L/3R

Problem. Backfires like crazy on decel, But also way to rich from idle to 1/4 throttle. ?????? how can it be to rich, and still backfire like crazy on decel? When in netural and reving it up, I see a puff of black smoke here and there, Wide open still fills like I need to go up 1 size on the Jets to 160/165.

It runs like a champ from 1/4 to 3/4.
Any Idea.
Revving the motor in neutral proves nothing...........
Try turning the fuel screw in some...........
 

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Discussion Starter · #4 · (Edited)
I'll try turning in the fuel screws a bit. Just wondering wont that make it backfire more on decel? Would I be beter off going to a 27.5 Pilot, and only turing the fuel screws out 1 1/2 turns? I hate that nasty poping when rolling all the way down a steep Sand Dune.
 

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I'll try turning in the fuel screws a bit. Just wondering wont that make it backfire more on decel? Would I be beter off going to a 27.5 Pilot, and only turing the fuel screws out 1 1/2 turns? I hate that nasty poping when rolling all the way down a steep Sand Dune.
Backfiring on decel can be caused by a leaking exhaust also. Check for leaks, even small ones. Aftermarket exhausts backfire easier then a stock exhaust, especially if the packing is burned out and if they have slip fits that are loose.........

Going to a 27.5 when you are already have running issues with a 25 at 3 turns out will cause your problems to intensify.

The fuel screw works in relation to the size of the jet, you cant really compensate by opening the fuel screw extra or less instead of changing the pilot jet size, since the range over laps in the jet size compared to the fuel screw setting.

From Experience, what I have seen is if you are at 1 turn or below slightly or at 3 turns or above slightly, it is better to change the jet accordingly, this gives you a better fuel ratio since you then can work with a better performing jet in its range rather then compensating for a pilot jet that is either to small or to large and at the end of its operating range............
 

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I'll try turning in the fuel screws a bit. Just wondering wont that make it backfire more on decel? Would I be beter off going to a 27.5 Pilot, and only turing the fuel screws out 1 1/2 turns? I hate that nasty poping when rolling all the way down a steep Sand Dune.
If you are at 4300 feet you won't need the 27.5. I ran that size pilot in stock carbs at 500 feet with fuel screws around 1 1/2. what does the spark plug look like after you rev out the bike in 5th gear and then shut it off. I agree with willy, I would set the fuel screws at about 2 turns and check for air leaks in the system. Also check the float height and make sure you're at 14mm.
good luck,
 

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Discussion Starter · #8 ·
Still haven't had a chance to work on it yet. I will check the floats first by doing the clear tube method. Do you guys think for my mods, and elevation at 4300 that the jets at 155 and 160 on GYRT jet kit are correct? 3rd clip(middle).
 

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Discussion Starter · #9 · (Edited)
Thanks for all the help guys, your suggestions worked great. I found the Problem, the left carb float was off, it was about 6mm higher then it should have been doing the clear tube method. The right carb was spot on. I got the left carb float right at 3mm above the split in the carb, and turned the piliot screw 1/2 turn in on the left carb, so now I'm at 2 1/2 left, and 3 right, and ground out all the extra material on the intake tubes between the carbs, and head. I haven't got a chance to ride it yet, but running in in the garage it sure sounds much better. Now when I hit the throttle I no longer see puff's of black smoke. Throttle is crisp:):)

What do you guys think on my main jets? is a 155 and 160 GYRT needles, and mukini jets right for my altitude at 4300 feet? I may just have to put a new plug in and ride it.
 

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Thanks for all the help guys, your suggestions worked great. I found the Problem, the left carb float was off, it was about 6mm higher then it should have been doing the clear tube method. The right carb was spot on. I got the left carb float right at 3mm above the split in the carb, and turned the piliot screw 1/2 turn in on the left carb, so now I'm at 2 1/2 left, and 3 right, and ground out all the extra material on the intake tubes between the carbs, and head. I haven't got a chance to ride it yet, but running in in the garage it sure sounds much better. Now when I hit the throttle I no longer see puff's of black smoke. Throttle is crisp:):)

What do you guys think on my main jets? is a 155 and 160 GYRT needles, and mukini jets right for my altitude at 4300 feet? I may just have to put a new plug in and ride it.
Sounds like you're on the right track, always good to check the floats and set them right. I can't say if your main jets are right, you'll have to ride the bike, listen to the motor and check the plug. I've only ridden at that elevation a few times back in the mid 1990s and I had to jet down 2 numbers on my carbs each time. Good luck
 
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