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needle jet??

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So here is what I have.

02 crf405r fully rebuild, crank, piston, valves.

everthing is stock except for a Fmf exhaust.

whenever i'm at a constant throttle fom 1/4 to 1/2 throttle, it surges (lean). when i ride it hard it responds very well and strong, its just at constant throttle. Previous owner re-jetted bc of the exhaust. The problem I'm having is i'll use the moose needle at its leanest setting clip 1 and it will bogg (way rich) then i'll swap it with the stock needle at its richest setting clip 7 and it will surge (lean)

It idles fine, starts right up WITHOUT choke. sometimes i actually use the hot start even when its cold, which indicates its slighly rich. thats why it odd its so lean at 1/4 throttle

how do I find a happy medium?


Stock pilot jet, screw 1.5 out

obekr needle

forget the main jet but it runs strong @full throttle

sea level 80F degrees

good gas, decent plug, vents are clear and float height is set, clean not over oiled filter :banana:

thanks for any help

Edited by DB 450r
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OBEKR is 1-degree taper, 78.25mm of taper, 2.755mm diameter (fat end), 1.2mm (thin end)

Going richer, try:

2 clips:

EKP (1/78.25/2.735) clip 5, or EKM (1/78.25/2.715) clip 3

4 clips:

EKP clip 7, EKM clip 5, EKK (1/78.25/2.695) clip 3

6 clips:

EKM clip 7, EKK clip 5, EKH (1/78.25/2.675) clip3

If the MJ hasn't been sized properly, none if this will help. "Runs strong" doesn't say that the MJ is the correct one for the weather/altitude. Have you tried disconnecting the TPS? That sometimes helps with constant-throttle riding.

Edited by davidl9999
had "going leaner" instead of "going richer" D'oh!
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You need to start at the beginnning and resolve each circuit. Not needing a choke talls me you are rich on the pilot. But, there is a simple method to check it.

Fuel Screw/Pilot Jet

Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.

Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.

*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***

Turn the screw in until the idle becomes rough or the bike stalls.

if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.

If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.

Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.

If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.

If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.

If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.

Next, you want to ensure the steady state operation between just off idle to about 1/4 throttle is good. This is the straight part of the needle (What the last letter of EKP -richer, EKM-Leaner EKR-Richer still, that David mentions). Then you can deal with needle length, taper and clip position.

After that is done, if you have any bog, that is dealt with by setting up the AP.

I have to ask, this bike is eight years old. Has the jetting always been messed up or is this some sort of new occurence?

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thanks for the info guys.

William1, good advice. I did what you said and already found an issue. I CAN turn the fuel screw in all the way without it stalling or even changing pitch. That would solve my running rich at closed throttle. I'm going to take it apart and see what size pilot is in there.

I bought the bike not running so I dont know its history. I fully rebuilt it, and I'm pretty much starting fresh. This is the last step for my rebuild is tuning it.

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Well I checked the pilot jet and its the stock 45. The manual recomeds the 45 jet at my conditions, I checked everything else. Any ideas on why the pilot ciruit is out of wack?

The stock needle is in good shape, and so is the fuel screw.

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When checking the fuel screw, you have to have the idle speed reduced as much as possible. A fast idle will have the bike partially running on the needle jet and confuse things. If.... the idle is as slow as possible and it does what you say, a new needle jet emulsion tube is called for. If you only change the pilot to compensate, you'll then have a rich issue off idle that you'll have to compensate for with a lean diameter needle, a lot of bother.

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  • 3 weeks later...


I did what you guys sugested and replaced the needle jet and emulsion tube. Once that didnt work, very fustrated, I reasearched it a again and you guys sugested disconnecting the tp sensor. Well I should have done that from the begining. I disconnected it and problem was gone!!!

I checked the sensor and according to the manual it was out of spec. I set it correctly, and that didnt help.

The sensor is within all the specs of the manual, and functions smoothly. I'm replacing it regaurdless, but my question is what is the chance that the CDI is bad?

Being that it ran GREAT without the sensor, I'm doubting its the CDI, just wondering what you guys think...

So glad to be making progress!


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You can try to (re)calibrate the TPS; the procedure is in the CRF manual (I don't know the setpoint values for your bike). Some folks just leave the TPS disconnected and don't bother with it, but it's not that bad to adjust and if it works, all the better. That said, there really isn't a downside to leaving the TPS disconnected imo as it only adds some advance to the CDI map at lower throttle positions; I don't imagine that you'd notice any power difference. But, you never know...

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I did recalibrate the sensor acording to the manual, and it didnt help. It seems that a lot of people do disconnect it. My theory if engineers took the time, money, and resources to use it in the design, that it should't just be disconnectd and forgotten.

I'm goin to spend the $50 and see if that does it. I'll let you guys know!

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I just bough a OBEKQ, its 1 size richer than stock. I'd figure i'd get that because i do have an aftermarket exhaust. I also have a needle that came from a moose jet kit. Surprisingly it seems to run VERY rich on that, so I don't use it. Once i get the new sensor I'll retune everything

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