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FCR MX39 Jetting (Yes... Another)

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Hey Guys!

 

 

I know there are pleanty of threads on this topic and I have pretty much read them all! 

 

 

I have just installed the FCR along with MRD/SSW (Open), 3x3, and K&N Air Filter.  I have the Flexjet fuel screw installed on the FCR.

 

 

My Settings are:

 

 

160 main jet
200 main air jet
EMN needle
clip 3
45 pilot jet
removed pilot air jet
2 turns fuel screw
o-ring mod

 

I ride around 600-1000 ft above sea level.

 

 

The temeprature right now is around 5°C and the summer it hits 25°C

 

 

The bike just dosent feel right.  performance wise it dosent seem to be all there.  from the videos I watch onyoutube the bike dosent seem to have that same snap.

 

 

What are some indications that would tell me I'm running to rich or lean so that I can begin to dial in my set up.  Also will the changei n teperarure in th summer make a large impact on performance?

 

 

My bike seems to pop ALOT on decel and I get a hanging idle.  Checked for leaks around the carb and there is not any.  Might be the throttle cable.

 

 

 

Any advice is greatly appreciated.

 

Edited by avis
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Did changng the needle fix your problem?

haven't swap needles yet.. but as it is my only issue is the hesitation(surging?) in the 1/4 throt range, not much popping or anything and im sure there's still a little more power to be had once jetting is sorted.

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Hey Guys!

I know there are pleanty of threads on this topic and I have pretty much read them all! 

I have just installed the FCR along with MRD/SSW (Open), 3x3, and K&N Air Filter.  I have the Flexjet fuel screw installed on the FCR.

 

My Settings are:

160 main jet

200 main air jet

EMN needle

clip 3

45 pilot jet

removed pilot air jet

2 turns fuel screw

o-ring mod

I ride around 600-1000 ft above sea level.

The temeprature right now is around 5°C and the summer it hits 25°C

The bike just dosent feel right.  performance wise it dosent seem to be all there.  from the videos I watch onyoutube the bike dosent seem to have that same snap.

What are some indications that would tell me I'm running to rich or lean so that I can begin to dial in my set up.  Also will the changei n teperarure in th summer make a large impact on performance?

My bike seems to pop ALOT on decel and I get a hanging idle.  Checked for leaks around the carb and there is not any.  Might be the throttle cable.

Any advice is greatly appreciated.

 

The bike just dosent feel right.  performance wise it dosent seem to be all there. ..

.It is surging or hesitating ??..... revving out freely.?

Are you getting full throttle.?

Fine tune your fuel screw with the procedure in the FAQ's

Edited by Craigo 485sm

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try out clip 4. i dont have an fcr i have the stock paper weight buttt. i had it on clip 3 and i couldnt go through rpms without my bike surging it felt like it wanted to die no power at all it was horrible i was cruizing 4th gear going 40mph very low rpms. so i switched my needle to the 4th clip position and it patched it up as well as the heavy pop on decel i still get a little pop but i can live with that its all fine tuning man, that what performance calls for!!

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The bike just dosent feel right.  performance wise it dosent seem to be all there. ..

.It is surging or hesitating ??..... revving out freely.?

Are you getting full throttle.?

Fine tune your fuel screw with the procedure in the FAQ's

 

The bike is hard on/off the throttle.

 

Should I dial in my fuel screw before attempting to adjust the clip position?

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Mate, I don;t understand what you mean by being hard on.off the throttle.....?

Of course fuel screw adjustment is one aspect that's needs to by addressed ...http://www.thumperta...ad.php?t=327405

Im not sure how to put it into words.  like just slowly rolling on the throttle it seems like an instant "shot" of power.  I'm not sure if thats just a characteristic of the carb.

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We have pretty much the same setup except i'm at <600ft elevation.  Others have recommended setting the OCEMN needle to the 4th clip.

 

As for your throttle cable, this shouldnt even be a question, you need to open the throttle up with everything attached and watch it snap closed swiftly, double check that nothing is hanging up on the frame or inside the throttle cam by taking the cover off and watching it close. 

 

idle hover happens when your bike is running very lean.  make sure you dont have any idle jets plugged with gunk, they need to be clean and clear.  check for blockages in all of your jets while you're putting the main needle on the 4th clip.

 

also make sure your airbox cover and seat is on before dialing in the fuel screw and then setting the idle.

 

good luck, report back.

 

Edit: forgot to mention, check your AP Squirt timing and duration while the carb is off the bike.

Edited by braaapopopop

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Im not sure how to put it into words.  like just slowly rolling on the throttle it seems like an instant "shot" of power.  I'm not sure if thats just a characteristic of the carb.

 

Sounds like the accelerator pump doing it's job.  :thinking:

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After swapping out the vacuum carb for the Fcr ,,throttle response is perhaps what you are experiencing....?

The Fcr has an accelerator pump and the mikuni bsr does not....

Is it bogging under normal throttle application when riding..?

EMN needle, clip 3 is good....

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After swapping out the vacuum carb for the Fcr ,,throttle response is perhaps what you are experiencing....?

The Fcr has an accelerator pump and the mikuni bsr does not....

Is it bogging under normal throttle application when riding..?

EMN needle, clip 3 is good....

 

Nope, dosent bog under normal conditions.

 

My 06 CRF250R had an accelerator pump, I even had to mod it in a similar way by using an O-ring.  This carb just seems much more aggresive on that initial hit.

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