2006 YZ450 Light Throttle Stutter



Having now got my YZ450 legal to road ride, I am experiencing a light throttle stutter. I have searched TT to find a lot of information on where to start looking, so tonight, I went for a ride and tried richening the pilot screw. This did help marginally but it also highlighted that on very light throttle, the stutter went, on light throttle (like cruise) the stutter is random, occasionally very rare to happen lower down (say 2500-3500) but mostly often stuttering getting worse at 4500-6000 rpm.


So I came home and checked the TPS. This is slightly out of spec. The closed throttle reading is 0.6 and WOT is 3.9. I removed the carb and adjusted the TPS to gain a higher reading, I only mustered 4.1 on maximum adjustment. I removed the TPS and noticed that the plastic locators on the switch were worn. I check the switches range off the carb and read 0.2 closed and 4.6 open. I'm going to order a new TPS as I think this one of worn.


Next I started removing the jets, everything is standard according the manual but the needle looks worn with obvious signs of scratching to it. I'll replace this too but having the stutter and having read what I have read regarding others experiences with this kind of hesitation, should I change the NFLR for a NFPR?


I'm not sure what to do with the rest of the jets, just leave them standard? 


The bike is pretty much standard apart from a twin air filter and a de-baffled '08 silencer (straight through). The bike also has the optional Yamaha power bomb front pipe. It seems to run ok other than the stutter, seems powerful and has little popping on deceleration although it did give a back pop on a gear change tonight but that is the only time it's done this.


Any help would be very much appreciated as it is a PITA to remove the carb on this bike lol.



Clean the stator harness

Inspect the stator pick up for ferrous debris

Replace the plug and gap at .9mm

Re-fit the plug cap to the wire, and inspect for cracked resistor solder

If you have not replaced the needle jet (emulsion tube) ever, you should. They wear out and oval causing odd jetting issues.

Also check all the ground connections in the harness(s)


All the TPS does it put you in one of three maps, if I remember correctly on the YZ ECU.

So, if you are toggling between two maps at a particular throtte position, you can change the TPS setting to move that transition to a less or more throttle open location.

I liked setting mine at .55 with the slide dropped (less than idle)

A YZ450, and particularly an '06, should not stutter on cruise at all. (mine doesn't, never did).  The TPS may be your suspect, inasmuch as the readings were incorrect.  Something to look at with them is whether the resistance readings change smoothly and in a linear manner as the TPS is moved from one end of its travel to the other, or if instead there are "holes' or "spikes" in the readings, which would indicate a faulty potentiometer in the sensor.  Since this year and model has no history of a cruise stutter as the WR did, I would start with unmodified factory settings when you replace yours.


If the needle is worn visibly, look at the hole in the top of the main nozzle.  It's likely worn as well (the hole should be round), and if so, you'll need both.  The NFPR is the correct OEM needle.  The difference between that and an NFPR is that the taper on the PR is higher on the needle by half the distance between two clip grooves.  In most cases, this is not really worth the change.  At the throttle position where your complaint occurs, it's unlikely that needle clip position plays into things very much, but it may.  If you have a lean condition between idle and 1/4 throttle with the NFLR, consider an NFLP, or NFPP, which will richen that throttle zone some. 

OK Thanks for the advice.


After Krannies post, I checked the tube the next morning and it is showing signs of where too so I will need to replace this. I rechecked the TPS and while slowly increasing the throttle position, the reading does increase with throttle position but if I stop increasing throttle position, the reading will stop and then drop back slightly, say 0.2 to 0.3 ohm. If a steady throttle position is held, once the reading drops back, it is steady. This is consistent right the way through its operation. As for the needle fitted, I got mixed up a little bit, the NFPR is the needle fitted which is as said, the correct needle for the bike. I have put the bike back together with the TPS set as best as it can be and with the needle clip in the next notch down to richen the mixture to see if that helps. I'll maybe get a chance to get out on it again Sunday so I will see if its any better like this.


With chopping the exhaust baffles out and the bike having the bomb front pipe, could this be a contributing factor to the characteristic nature of this stutter?

The exhaust shouldn't affect it, although virtually nothing actually fixes that muffler.  Several folks have cut out both cones from the muffler and never developed any such driveability complaints as a result.  Does make the pipe rather much louder, however, what with its short overall length.  I'd be surprised if it passes any kind of actual sound testing.


The .2 ohm shift could be a number of things, including minor problems with the test leads, something internal in the meter, or even your body capacitance, if you're holding your leads in place.  As long as the resistance rises and falls evenly throughout the range, I'd ignore it.


In as much as you have found wear in the main nozzle and needle, I'd wait and see until after you get the new parts in the carb. 

Thanks Grey. I'll save a few quid and try the needle and tube first. Hope I won't need a TPS :)

Oh, and the 08 silencer de coned as you say is too loud. Big mistake. I've ordered a White Bros Pro full system so hopefully it will attempt to quieten the engine bark.

Edited by Nick280

So got out on the bike tonight. Although lifting the needle and tweaking the TPS seems to have reduced the stutter as much as maybe stopped it higher up the rev range, but it is still there. So I came back home, lifted the tank and disconnected the TPS. Went back out and Gone! The stutter has gone completely. It was great. I did notice the bike behaved differently though and I'd not be happy with it running like this permanently. Its harder to start. Not hard, but harder. The bike feels lazy on light throttle, like there is something wrong (I guess like the TPS is disconnected). It pops and cackles like mad too on over run but only with a touch of throttle (sounds great). So, what does this tell me?? Do I need a TPS or does the TPS compensate for lean low rev running by richening the mixture? Should I just order the suggest needle and tube or get the TPS too?


Help please :)


Oh. This thing is mental!! I've swapped the 49T rear for a 44T and kept the 13T front and it still wheelies in 2nd like my old KTM 660 SMC did in first. I've a 14T to go on the front which I was a little hesitant to do, but I think the bike can handle 14/44 on enduro wheels and 14/38 with supermoto wheels and still be a fun bike to ride!! Cant wait to drop the oil when its run in and see what 8k+ rpm is like. 

TPS failed.  There were a few of those.  They read OK, but handling 5 volts is different than just a meter.


You can run with it disconnected.  It isn't ideal from an efficiency standpoint, but there's no danger in it.

OK, so a little update on where I have got to with this. The new TPS came along with NFPP and NFPQ needles. Fitted the NFPQ needles with the clip in position 4. The bike did have an NFLR needle fitted as standard and as per my manual, not the NFPR.


So, out on the bike the stutter has gone right up to around the 5 to 6krpm mark now and I think it is worse (or just more noticeable) now than it was. The bike feels a little less sharp low down but start brilliantly from cold and hot and ticks over smooth at 2krpm with the pilot screw 3/4 turns out as per manual. On over run it pops like I hear a little of WR's do on Youtube but cant say I've noticed many YZ's do it. Its not excessive but it did't do it before. My thinking is lift the needle up a notch (clip down). Do you think this is the correct thing to do. Over the NFLR, the needle is already half a clip richer. 


Thanks for any help.

Edited by Nick280

What year is the YZ450FW? and What year is the YZ450FV?


YZ450FZ is 2010

YZ450FX is 2008


so is YZ450FV 2006 

and YZ450FW 2007?


Just noticed in my manuals, the YZ450FW should have NFLP needle but the YZ450FV should have NFPR. I printed the manual that came with the bike (YZ450FW) but downloaded a 2006 manual too (YZ450FV) before I realised the bike came with a manual. I didn't really pay to much attention to the W & V bit until now.


I'm kinda thinking my bike is a 2007 now.........?


Would that make sense??

Read two things:


The tenth character of the VIN ("6" is an '06; "7" is an '07)


The number on the left side of the carb.  ('06 should be "2S21 00" ;  '07 would be "2S27 70" )

Fortunately the TPS's have the same part number lol

Lifted the needle up a notch and it's worse. Quickly loosing interest in this bike now. Any advice on what to do other than trade it for a KTM :D

Lifted the needle up a notch and it's worse.



That would lead me to lower it. 


Did you adjust the TPS by the manual, with the engine running?

Did did adjust the TPS but not with the engine running. That wasn't clear to me. I'll reread it.

I did think maybe dropping the needle to a position below where it was. Would it create the same miss if rich rather than just being boggy?

Bollocks. Hmm, that might help. I'm going to have to make a tool for slackening that TPS screw.

Eventually got over my 2000mile Scottish tour in 5 days on the trusty 1190 Adventure and found to time to play with the YZ again. I've adjusted the TPS to give 6.8v at idle. I chose this figure to be midway between the 5.8-7.8 stated in the manual. Had a good run out on it yesterday  and things have improved but I still have an occasional mis at 4500-6000 ish rpm. Low down this is perfect, no hesitation and no miss (occasional popping). The miss is more noticeable in say 2nd or 3rd gear then 5th. Again, anything from say 2/3rds to WOT is clean. I'm thinking lift the needle/drop the clip. Would I be thinking in the right direction? 

That's what I would do.

We were on the right track, just heading in the wrong direction. Lifting the needle a notch (richening from position 5 to 6) made the miss worse. I ended up dropping the needle 2 notches from where I started this morning (NFPQ now in position 3 from 5). It is a lot better but still has the miss which is now higher up in the rev range. Now I get a loud pop from the exhaust very occasionally on gear up shift and louder popping when decelerating.


I think the miss seams to be happening at a load transitional period, not always throttle position related. Lighter loads on the engine at set revs will provoke the miss and exhaust to pop. For example, climbing a slight incline at say 5500rpm with steady throttle and engine runs fine. Crest the hill and start going down the other side and the engine will start missing and the exhaust popping. This makes me think I maybe should have stuck with the standard NFLR needle instead of going with the richer NFPQ. The bike runs really nice at 2500 to just below 4000rpm and like a train on wider throttle openings (I think it is sharper now on wider throttle openings than when I started this morning). I've noticed a lack of the bike wanting to set off too, like opening the throttle slightly as you do when setting off slowly makes the engine actually drop in revs a tiny bit (I think its called bogging) until it clears it's throat and then it revs up. It could have done this before but now the bike is generally running better, I maybe just starting to notice this.


Any opinions on my thinking would be great thanks.


It is a fun bike. I think I have the gearing bob on for road riding with enduro wheels and I really don't mind putting it away wet and dirty which now we're having a crap weather spell here, is keeping my 1190 nice a clean and me my sanity :D In fact, we are having thunder and lightening right now. Time for a brew and to observe one of natures most spectacular shows me thinks!!

Next place i would suspect is the fuel mixture screw based on what you are describing. Richen it by turning the screw out in 1/2 turn incriments to see if things improve.

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