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Old 01-30-2015, 08:05 AM   #1
pma4x4 OP
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Joined: Oct 2014
Oddometer: 26
Preparing FCR-MX39 carb for XR650L

I had acquired a FCR-MX39 carb for $80 and verified its numbers with Sudco and it is from a 2007 WR450F. I plan on tearing it down and cleaning it, as it looks like it needs it. After a lot of reading and research it looks like I will go with DOT-COMs jetting recipe.


My bike specs:
2008 Honda XR650L
stock engine
desnorkeld airbox with Unifilter
Desmogged
FMF Powerbomb header
FMF Q4 muffler

Pretty much identical to DOT-COM which is why I was going to go this route. For those that don't know DOT-COM actually installed a wide band o2 sensor and tuned his FCR-MX40 to perfection. a few others that have a similar setup like his have used his recipe with great results essentially making it a plug n play setup! My bike is setup identical to his so this is the setup I am going with.

I am just wanting to verify the components since the last bike carb I worked on was 20 some years ago.


the jets currently in my FCR is as follows:
MAIN JET - 162
PILOT JET- 45
STARTER JET- 65
LEAK JET - 60
PILOT AIR JET - 70
MAIN AIR JET - EMPTY (the picture of the air jets is of my carb)

This is what DOT-COM (over on Thumpertalk) is using and I want to make sure I have his abbreviations correct

MJ158 (MAIN JET)
PJ42 2turns out (PILOT JET)(TURNED OUT???)
PAJ100 (PILOT AIR JET)
NCVT needle 2nd clip
R&D leak jet just cracked open 1/4 turn, if you don't have an adjustable leak jet then use the smallest (35) or completely block it off. (LEAK JET)

Change just these ones and leave all other jets alone? Should I have a MAIN AIR JET?






pma4x4 screwed with this post 01-30-2015 at 08:57 AM
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Old 01-30-2015, 10:49 AM   #2
sandwash
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Location: Flagstaff Az
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This the set up for dr650,this after alot of A/R dyno testing.Unless someone has done it before it going to need some A/R testing to get it right.
Jet list (sea level)
    • 155 main
    • EMP-4.5 needle (4th clip down + .5mm shim)
    • 40 pilot
    • 100 pilot air (Yamaha P/N 5TA-14943-27-00)
    • 200 main air (fixed size on OEM carbs)
    • 35 leak
    • Slide cut-away mod (increase arc by .5mm)
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Old 01-30-2015, 11:22 AM   #3
pma4x4 OP
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Thats what DOT-COM over on TT did was use a wideband o2 sensor and figured it all out. with my bike being pretty much idetnical to his I should be able to use his recipe and call it a day.
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Old 02-25-2015, 06:30 AM   #4
D0T-C0M
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Quote:
Originally Posted by sandwash View Post
This the set up for dr650,this after alot of A/R dyno testing.Unless someone has done it before it going to need some A/R testing to get it right.
Jet list (sea level)
    • 155 main
    • EMP-4.5 needle (4th clip down + .5mm shim)
    • 40 pilot
    • 100 pilot air (Yamaha P/N 5TA-14943-27-00)
    • 200 main air (fixed size on OEM carbs)
    • 35 leak
    • Slide cut-away mod (increase arc by .5mm)
I have found that at partial throttle the EMx needles exhibit a lean condition at 0-3/8 throttle. I found the NCVx needles, which are dual tamper needles, to correct the AFR to perfection. The EMx and NCVx needles are identical from 3/8 throttle to WOT. Maybe cutting the slide slightly like you did addressed this same lean affect as I observed.

D0T-C0M screwed with this post 02-25-2015 at 06:38 AM
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Old 02-26-2015, 09:10 PM   #5
jesusgatos
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Location: on the road
Oddometer: 2,393
Thanks for posting this info. Will be helpful when I get these bikes running.
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