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Keihin FCR37 on wr250 2005 1/3-3/4 throttle issue

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Hi Guys, 

New to the forum (I am one of the audio guys on a famous Harley forum - same forum name)

I am at a loss at this point in time... I am pretty savvy from a mechanical perspective, did my research, etc etc.

Need bike (2005 WR250F - Keihin CRF carb) running smooth for trip july 10th with bro.

So the basics:

- based in Las Vegas (~2500ft above sea level)

- carb is CLEAN, spark plug at .6mm, clean new air filter

- float set to 8-9 mm

- starts up without an issue

- got manual adjustable A/F needle - set to 2 -2.5 turns out (@ 2.5 seems to run a tad better)

- jetting: Pilot #42, Main #175, leak jet #95! (high compared to stock according documentation) - Needle I cannot find a code on it

- EDIT: needle clip in the middle on position 4.

Symptoms:

+ stationary - starts and runs fine

+ upping throttle to 1/3 RPMs increase "smoothly"

+ full throttle: hits the RPM limiter so IMO no issue

- Quick WOT > bogs (I believe that is what you call it) and dies (I can live with that, but not the next one) - I fiddled with the accelerator Pump timing at tad, keeping track of the original setting; did not seem to get rid of the WOT issue.

- 1/3 - 3/4 throttle : it ?surges?... I mean RPMs go up and down in like 2-3 times per second (this is all not loaded so in the garage; When riding bike has the same behavior)

when reading articles on the web and youtube's, it "points" to the main needle, right? or perhaps the leak jet is way too big...?

I appreciate your help/comments/suggestions... 

If need be I can shoot a video...

Edited by AAWAV
add'l info

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Put in a #45~#50 leak jet, that will fix the bog.

#42 pilot jet is too small, try a #45 with the fuel screw at 1.75 turns, that should be about right.

ALL WR250F's surge at steady throttle. It is a fault of the CDI design map. Nothing you can do about it but an aftermarket CDI (Vortex or DynaTek). The WR's were never designed to run a steady throttle, they are woods racers. Yamaha did not put the effort into a map that worked like you want to ride the bike. In normal woods riding, you are constantly working the throttle so the map issue is never a problem. Just when on fire roads at a constant speed.

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Thanks! I will get the jets. Weird that wr250 map is set up that way. It's an off road on road bike.
How about yz then if I may ask...
Same engine right? Bike I only use for off road as spare and. Ik for my brother when in the usa.
Done this as long as I got it. Crf250r I got runs totally fine.

Again appreciate you help and I know it takes a lot of time to be a moderator. I am not one but put countless hours into harley sound systems including bench testing etc.

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Digger on the internet and found some info...can I put yz cdi in and cut the grey wire? If so, do I need specific year? Would it work with current jetting?

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1 hour ago, AAWAV said:

Digger on the internet and found some info...can I put yz cdi in and cut the grey wire? If so, do I need specific year? Would it work with current jetting?

No

Yes

No

Won't work

YZ has a different crank end/stator/rectifier/wiring harness/cdi/stator

The gray wire mod will not solve a jetting and factory defective ignition system problem.

 

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understood... last question: what about the Dynojet 4125 jet kit? would this one help/improve the above?

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Nope, I'd keep the jetting I rec. DynoJet jets are unique to them and if you use them and need to replace a jet or make a change, you must only buy from them. So I am no fan of DynoJet kits (most other kits are repackaged DynoJet ones, so only get a kit if it has OEM Keihin jets in it).

Some like the Yamaha needle: 5TA-14916-YS-00 .NEEDLE (#NCYS)

Others have bought James Dean (JD Jetting) kits for his proietary needle. TRuithfully, thje NCYS is probably the best choice (clip #3) though many do not notice a difference from stock. Your needle should have a code stamped on it. No code? Is the top colored (red or blue)?

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ordered 45 pilot and 48 leak (as you mentioned 45-50; so went with the one in the middle ;)) from RMATV... should be in tomorrow (it usually is in in 1 day due to short distance)

I checked the bike and noticed the airbox mod was done as well as the grey wire mod. will check the throttle screw mod as well (got a feeling that one is done as well...)

will do the acc. pump o ring mod (got metric o rings here laying around so either a 6-10-2mm or 7-11-2mm). .

will double check the needle wearing stronger reading glasses... needle clip currently on 4 (1-7)

carb is a PITA as I need to remove it to fully access it (safely)

again - thx for all your help.

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