xr650l new carb or daves mod?

Ive recently purchased a 2007 xr650l. The mods the guy had before me were removed snorkel, removed smog, and slip on white bros exhaust. Ive read some on daves mod and how it improves performance drastically. Also a new jet kit would be required. Ive also read that its better to get a keihin fcr mx 41 and rejet it then. which solution would give better power and by how much?

You won`t gain a pile with either,look at it as a rideabilty improved throttle response with either carb mod..


rejet the CV carb 52 pilot and 152 main to start,,you might need to go 55/155 but don`t go there unless it`s still not burning well,,throwing more fuel at it does nothing except carbon the engine up.....


You will gain throttle response with the FCR MX.......it made a huge change in my bike,,doesn`t mean you gain more horsepower,,but sure feels like it,,you wack the throttle and she goes........the VC carb will always hesitate.......i also improved fuel mileage with the FCR MX..better fueling can equal better

fuel mileage..



throwing more fuel at it does nothing except carbon the engine up.....

The engine runs a bit cooler with a richer mixture.  A little more than "nothing".



When I first bought my XR650L I rejetted just to be sure what jets were in there.  I think it already had basically the same jets, but now I know for sure what's in there.


If the bike runs well right now, you might not need to do anything to it.

I am just going to reiterate what Brian said.  FCD-MX is the best most noticeable mod.  Doesn't give you any more horsepower by itself but huge HUGE difference in throttle response.  The CV carb cannot even come close

Edited by D0T-C0M

i believe that is a FCR MX....someone can correct me if i`m wrong.......there has been updates to the carb over the years though..the newer version has improved accelerator pump linkage..a cutout at the bottom of the slide,etc.i would get a newer version....just wait till you find one at a decent price.the 2007 CRF450R is what i got....you can use the CRF250R carb too at 40mm.......


either way get one with the throttle assembly if you can,less twist to wide open,,and also you need the hotstart cable so you can use the hotstart cable with the XRL choke plunger,,that way you have handlebar choke control like the OE XR650L has,no bending and trying to fish for a manual choke pull :thumbsup:



sweet,nice one,i`d get it..........


The FCR MX has 2 ports,one is a choke,the other is a hotstart port.........


i`ve never seen anyone need the actual hotstart,so,,what you do is unscrew the FCR choke pull and plunger,,screw it into the hotstart hole in the carb........


then take just the choke plunger end off the XR650L choke cable.........put it on the hotstart cable are not using from the FCR and screw it into the FCR carbs bchoke hole......


So what you end up with is the FCR hotstart cable with the XRL choke plunger end screwed into the FCR carb,the other end of that cable goes to your choke handle on the handlebars so you can operate the choke there..


the reason you want the FCR hotstart cable as a choke cable is simple,,,,,,the OE XR650L choke cable cannot be used on the FCR,,you need the FCR hotstart cable as it has a 90 degree bend..the XRL cable does not...


D0T-C0M  has a jetting recipe here for that carb.if you follow it`ll be so close on the jetting that you`ll leave it be after,,runs really good......


You`ll only need a NCVT needle and 2 jets...a 42 pilot and 158 main if i remember correctly..message   D0T-C0M   here,he knows far more than i do,,and is great at helping guys with this conversion..



Edited by brianhare

oh,,you`ll need a NOSS adapter to adapt the airbox side of the carb.....


this one  http://www.nossmachine.com/honda_quad_parts.htm  fits Honda quads,,same,same......works perfectly,,you JB WELD it in place.....making sure to not plug the ports and that`s lined up perfectly,easy stuff.....



Here`s mine with the BOYESSEN adjustable leak jet and NOSS adapter...


























Actually Brian I do use my stock choke cable with the hotstart plunger end piece connected to it.  I put stock plunger end on the hotstart actuator and screwed that in.  I never use the hotstart, not sure when someone would use it.


As far as information everyone considering this mod should read at least the first 8 pages of this thread.  This thread has everything you need to select the proper FCR-MX carb and setup your new FCR-MX carb.

would i look for a jet kit or specifically look for a NCVT needle, 158 main, 42 pilot jet? Or would those items be included in the carb i purchased http://www.ebay.com/...cd8c91e&vxp=mtr. Or possibly could i buy a dynojet jet kit and purchase a NCVT needle, or should i search for each part alone?

I just used a hotstart knob ass from the early YZ/WR 400/426 to plug off hotstart well it works you can reach down and use it I never do. And just use the stock FCR choke knob you only use choke when cold I can reach down and pull knob when needed. I can get to knobs as im using a 600 crankcase breather setup no oil seperator

would i look for a jet kit or specifically look for a NCVT needle, 158 main, 42 pilot jet? Or would those items be included in the carb i purchased http://www.ebay.com/...cd8c91e&vxp=mtr. Or possibly could i buy a dynojet jet kit and purchase a NCVT needle, or should i search for each part alone?

There is no kit that I know of that includes my jetting recommendations.  You will have to purchase separately from the dealers.  Besides any jet kit I've since is grossly overpriced.

ive aquired the carb and the noss adapter, but they dont fit, should i grind the rim of the carb to fit the adapter?

Yup,,slight grinding of the lip is required for the new NOSS to slip on..



This is the definitive thread for FCR conversion. Thanx to all contributors. I may try it down the road now that it's all so clearly defined.

Just ordered the NOSS adapter and snagged a carb off of a 2007 CRF250r on the cheap.  Im starting to think there aint going to be much stock left on my 2014! LOL  Thanks for all the great info folks!!

Ive obtained and installed my fcr mx 41mm carb and it idles nice except when i gas it, it bogs, ive moved the fuel mixture screw from 2 to 4 and it still does the same thing. Im mot sure if i positioned the needle on the right notch. I did position it 3 down but there is 7 positions so i wasnt sure from what side to do it from. i cut the hotstart cable off and tried to install the original choke but the screw was completely stripped so i reattached the old choke. everything fits nicely but i hear a constant higher pitched rubbing, but its gone down as the bikes been running. 

nathanslocum what jetting are you running? If you run my jetting at 0'-1000' elevation you should be on the 2nd clip from the top. 


I recommend


158MJ (over 90f use 155MJ)

NCVT needle 2nd clip from the top

35 LeakJet or completely soldered shut


p.s. you do not use the pilot screw to fix a bogging problem.  The pilot screw is calibrated using Eddie's Method here.   The bogging issue can be caused by several things but some questions I would have How long is your squirt duration? Is the stream hitting the slide? What year is your FCR-MX carb do you have? Older FCR-MXs require a linkage/spring mod.  Is your AP linkage setup correctly?

Edited by D0T-C0M

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