wr426f misses at constant speed and 1/4 throttle, help
Posted May 27, 2003 - 09:00 AM
When at constant speed (i.e. dirt road) and about 1/4 to 1/3 throttle, the bike has a miss. If I roll the throttle, it's ok. It seems to be rich just at the spot. Anyone know how I could fix this. Is it the needle setting? It seems I have to take the carb. completely out to change the needle setting, right? Any advice and help would be appreciated. PS. I think the needle is set to the stock position.
Posted May 27, 2003 - 11:01 AM
But it does sound like you are rich on clip position. Stock should be fourth from the top, given the huge main and pilot in there I don't think we can assume the needle is in the stock position or even is the stock needle. If you rotate the carb around the other way you should be able to get the needle. You need to remove two allen head bolts to remove the top cover, this exposes the slide. In the top of the slide is another allen head keeper screw, the needle is underneath that.
Hope this helps.
Posted May 27, 2003 - 01:45 PM
Posted May 27, 2003 - 02:37 PM
Posted May 27, 2003 - 03:57 PM
If I change the needle to the YZ needle, won't that mean that I have to rejet the pilot and main also? Also, if stock position of the WR needle is 4th from the top, that means I have to go fifth from the top to make it leaner, correct?
The only difference WR to YZ 426 jetting-wise is the needle and the Pilot Air Jet. Pilot, Main, and Main Air Jet are the same. The smaller PAJ on the WR (75 vs. 100 for the YZ) actually works okay with the stock 42 pilot fuel jet, but if you run a 45 you will definitely want the 100 PAJ.
Also, you have the clip position moving in the wrong direction. To go leaner you want the needle to stay down in the main, letting relatively less fuel out for any given slide postion. So you move the clip up which drops the needle down.
Hope this helps
Posted May 27, 2003 - 04:09 PM
Just changing to a YZ needle will make your situation worse.
Not necessarily. Why would you say that? The stock WR jetting works okay with the bike corked up, but once you lose the restrictions, you are for all (jetting) intents and purposes operating a YZ motor.
Check what type of needle you have in the bike and then go to a larger diameter needle. I mic mine to verify which needle to use.
A good idea, but the PN/Needle Code will tell you the diameter. Also, he states the problem occurs 1/4 to 1/3 throttle, so that would be on the taper and beyond the straight diameter. Maybe I don't have enough zeroes in there, but I'm getting a diameter of .10847 for the stock WR 426. It is 2.755 mm, somebody check my math.
The 426 is different but I would research some more before you just buy a too rich standard YZ needle. The stock needle works better with uncorked pipes.
In my experience the stock WR 426 needle most certainly does not work better with uncorked pipes. You are the first person I've heard say that.
That don't mean you ain't right and I'm wrong but I wouldn't bet on it.
Posted May 27, 2003 - 04:19 PM
This is a known problem with some 03's and you will find a ton of info regarding the new bike. Our info will be back on about page 50 for the 01's but its essentially the same issue that Yamaha never fixed. I guess that they figured that no one who notices this miss is not actually racing so it is not worth the effort to fix. Also search for Vortex ignition which will eliminate this but for $$$.
Just my 2 cents.
Posted May 27, 2003 - 07:12 PM
Posted May 27, 2003 - 08:57 PM
Just to correct my opinion. I am refering to the stock YZ needle works better with an uncorked pipe (not stock WR needle). Sorry for the confusion. The WR motor with WR cam timing will need a different needle than the WR motor with YZ cam timing. At a quarter throttle my needle diameter has a bigger effect than the taper. Taper has a bigger effect from 1/3 to 3/4 throttle openings. Just my experience with the 5 needles, WR and YZ cam timing and pipe with insert, uncorked, and aftermarket pipe as well as twin air filters. That is why I am saying to pick the right YZ needle diameter for his mods. I agree that the stock YZ needle will work for the high flow modded bikes with YZ timing.
Posted May 28, 2003 - 09:45 AM
The WR motor with WR cam timing will need a different needle than the WR motor with YZ cam timing.
I also thought the different cam timing might affect the jetting, but in my experience I just couldn't tell. Whatever the affects are, it is too minor for me to detect riding one bike after the other (uncorked WR vs uncorked and YZ timed WR, both ran equally well with the E taper needle).
I changed the cam timing on my '00 YZ with some adjustable wheels and didn't notice any difference. Of course, the changes I made weren't as drastic. If you radically changed the valve lift all bets are off, but I'm not sure if I can see how an exhaust timing change would substantially alter the way the motor breathes. Just my own thoughts on this issue. I guess it is good to see some different opinions and experiences.
Anyway, I agree with you that it is likely a jetting problem. I have heard of CDI problems leading to fouled plugs, and I know the 250Fs had CDI issues, but I haven't really heard that on this board.
Wrkaholic, your last post makes me want to agree with Indy on the cause. I'm leaning towards diameter and/or pilot circuit and not clip position (when you accelerate I'm thinking you are now on the taper, the "cruise control" comment tells me straight diameter and pilot/idle).
Mabye the first thing you should try is a leaner idle mix. Go in 1/4 turn increments, unlike a two stroke the idle mix screw governs fuel, not air, so going in (clockwise) is leaner. The idle mix is recessed in the bottom of the carb bowl.
BTW, I'm fairly certain stock main is 165, YZ I know is a 162. This makes sense when you consider the D taper needle in the WR, the E taper needle will open things up more quickly and will prefer a smaller main all else remaining equal. Both bikes come with a 42 pilot.
You said you were at 3,000 ft. I would think you are borderline 40/42 pilot, stock main should be okay, but a 162 may be better, particularly with the YZ needle. If you do get that YZ needle try fourth clip first (this is stock setting on most bikes actually), then go to the third which might be better for your altitude.
Hope this helps.
Posted May 28, 2003 - 11:52 AM
Posted May 28, 2003 - 01:31 PM
Hick and others thanks for your reply. I ride in Hungry Valley (3K' to 5K'). I talked to the previous owner and he told me the needle is a EKP in the 4th position.
That is nearly identical to a stock YZ needle, to be exact it is one half clip leaner.
I'm at 4,000 ft. in the desert, here is the jetting I ran on my '00 and '01 YZF:
200 main air jet (stock)
1.5 turns out on the idle mix
~ 85 pilot air jet (via and adjustable screw I bought from Sudco)
EKQ # 3 (this is just slightly leaner off the pilot than your EKP)
So your jetting is pretty rich relative to mine. A 170 main jet is at least a few sizes too large for you, so this may be sort of polluting other circuits. To that end I think you should put a 162 or at least a 165 in there before you do anything else. Then ride the bike, if the problem persists I would suspect the pilot jet before clip postion but who knows, relating the condition over the internet is an inexact science at best.
Hope this helps. Please let us know what happens so we can get this problem sorted out.
Posted May 28, 2003 - 08:24 PM