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2008 450 Exc decel pop

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Well I need some help. My new to me 2008 450 exc has a severe decel pop. It has been jetted, slip on pipe and emissions equip removed. Should I start with rejet?

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your mixture screw should be no more than 3 turn out, if it's out 3 turns and still pops on decel you need a bigger pilot. 48 is stock, people often put 42 in from the jd jet kit. Also if the bike sat for awhile the jet could be plugged. Start be checking how many turns out the mixture screw is.

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Which is the mixture screw? the one further into the bike on the carb?

Or the one that is on the outter most area of the carb and runs like a wire back behind the carb?

The previous owner jetted it, and no jd jet kit...

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Which is the mixture screw? the one further into the bike on the carb?

Or the one that is on the outter most area of the carb and runs like a wire back behind the carb?

The previous owner jetted it, and no jd jet kit...

The fuel screw is the one pointing down by the float bowl.

If you don't already have it, order a longer one with a knurled knob

so you can get to it easily when you change altitude/temp.

The one with the wire is the idle speed.

What was the fuel screw set at?

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The fuel screw is the one pointing down by the float bowl.

If you don't already have it, order a longer one with a knurled knob

so you can get to it easily when you change altitude/temp.

The one with the wire is the idle speed.

What was the fuel screw set at?

Ok I haven't checked it yet, I wont be home till tomorrow, I know it is an extended aftermarket 1, I will check it tomorrow, what do you recommend? I ride at 2,000 ft. to 4,000 ft. usually. Like I said it only has de-smog and a slip on pipe.

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Every bike is a little different and it depends on what the PO put in for a pilot jet.

What altitude and temp. was it popping at?

I'd start out at 3 out like a prev. poster said and see if it still does it.

Remember that it will be more likely to pop lower and colder and when it's not fully warmed up so

if you ride at 2000+ and 70F but test it at sea level and 60F,

it will pop anyway at the right setting for the higher/hotter location.

Make sure it's warmed up and in similar conditions and test it at three turns out.

If it stops popping, turn it 1/4 of a turn and test again, repeat.

When it starts popping, go back out 1/4.

I also do a response test and mine actually responds best at the first 1/4

when it starts popping so that's where I run it with a slight pop.

If it pops at 3 out, you need to go to the next larger pilot.

He prob. put a 42 in and you might need a 45.

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Every bike is a little different and it depends on what the PO put in for a pilot jet.

What altitude and temp. was it popping at?

I'd start out at 3 out like a prev. poster said and see if it still does it.

Remember that it will be more likely to pop lower and colder and when it's not fully warmed up so

if you ride at 2000+ and 70F but test it at sea level and 60F,

it will pop anyway at the right setting for the higher/hotter location.

Make sure it's warmed up and in similar conditions and test it at three turns out.

If it stops popping, turn it 1/4 of a turn and test again, repeat.

When it starts popping, go back out 1/4.

I also do a response test and mine actually responds best at the first 1/4

when it starts popping so that's where I run it with a slight pop.

If it pops at 3 out, you need to go to the next larger pilot.

He prob. put a 42 in and you might need a 45.

Hey Carver thanks a ton, I will do this tomorrow and let you know how it goes.... Thanks for posting so quick. Ill let u know, otherwise Im loving the Pumpkin... :thumbsup:

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Hey Carver thanks a ton, I will do this tomorrow and let you know how it goes.... Thanks for posting so quick. Ill let u know, otherwise Im loving the Pumpkin... :thumbsup:

You're welcome.

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Every bike is a little different and it depends on what the PO put in for a pilot jet.

What altitude and temp. was it popping at?

I'd start out at 3 out like a prev. poster said and see if it still does it.

Remember that it will be more likely to pop lower and colder and when it's not fully warmed up so

if you ride at 2000+ and 70F but test it at sea level and 60F,

it will pop anyway at the right setting for the higher/hotter location.

Make sure it's warmed up and in similar conditions and test it at three turns out.

If it stops popping, turn it 1/4 of a turn and test again, repeat.

When it starts popping, go back out 1/4.

I also do a response test and mine actually responds best at the first 1/4

when it starts popping so that's where I run it with a slight pop.

If it pops at 3 out, you need to go to the next larger pilot.

He prob. put a 42 in and you might need a 45.

Awesome post. Thank you for the information.:ride::lol:

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not sure about the new motors but with the RFS motors/exhausts i always had a burble and minor popping on closed throttle decelerations... :lol:

...that is...until i sealed the motor to header junction and header to exhaust junction w/ ultra high temp silicone(copper). :ride::thumbsup:

ur problem/solution cud be as simple as that.

cheers

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not sure about the new motors but with the RFS motors/exhausts i always had a burble and minor popping on closed throttle decelerations... :lol:

...that is...until i sealed the motor to header junction and header to exhaust junction w/ ultra high temp silicone(copper). :ride::thumbsup:

ur problem/solution cud be as simple as that.

cheers

+1. Severe decel pop is a sign of an exhaust leak

a little popping on decel does not mean you're lean on the pilot jet. a lot of decel popping means you could be lean...but you also could have an exhaust leak. A little is ok, a lot is not.

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My 06 450 exc was popping really bad when I brought it out this year. I re-sealed the exhaust and its like brand new again, not a sound. I would start with that and see what happens before taking the carb apart. If it didn't do it before I would suspect the exhaust leak. Carburators just don't fall out of adjustment periodically

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I actually installed the Lexx exhaust and it pops less, but it's still popping here. Time to see if it's too lean.

It will be even leaner with the aftermarket pipe.

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It will be even leaner with the aftermarket pipe.

Why would it be leaner with an aftermarket pipe? I thought it was determined by the carb, not the exhaust on the other side of the engine?

And the kid that I bought this from took the stock exhast and took apart the pipe and made it straight pipe.

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