Yz 426 2001

nikki

Moto Junkie
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#2
Red (my fiancé) has had his since January - races/rides nearly every weekend... and hasn't had any problems with it. Of course he routinely changes the oil/oil filter. It's all still stock too.
 
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#5
Problem...

This bike is brand new (i've put 3 hrs. on it trail only). After it warms up, it is running rough at 1/4 to 3/4 throttle. It also frequently fouling plugs. The main jet has been changed from a 162(stock) to a 150. The dealer also suggested changing the accelerator pump from a 8mm stroke (stock) to a 7mm, which I did. I fouled a plug just recently and am seeking any suggestions....
HELP!!!!
 
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#6
Could be jetting, could be the CDI, if you have any buds that own 426's swap the CDI and see if that's the fix and if it makes their's run bad/foul plugs. Also, check out Thumpertalk.com, there is a yz/wr forum w/loads of info, do a search for the "bk mod" it makes for further adjustment of the ac pump, lots of knowledge on that board. Good luck.
 
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#7
How is it fouling plugs? Obviously not oil-fouling. Is it fouling due to excess gas? Are you sure the plug is fouled or is the bike flooded, etc. and you are having to put in a new plug to get it fired?

You problem sounds very unusual. I've had 2 YZF's (98 and 00) and have never had any problems - once I finally learned the starting bugaboos.

If you're convinced that the problem is real (vs. a deficiency with your starting methods, etc.), you need to get the dealer to provide more help. From my experience and reading over the last 3 years, the stock jetting and accelerator pump should be very good (versus a 2-stroke that almost always requires fiddling). Although many others may refine their YZF settings, one should be able to get good, reliable performance from stock.

If you're not convinced that your starting method is not at fault, I would suggest the following:

1. Look for a early 2001 Dirt Bike article (s/b on their website) on 4-stroke starting that listed the methods employed by Hawkins, Watts, Kiedrowski, Summers, etc. on their various thumpers. The methods and comments helped me understand the YZF starting drill rather than simply memorize it. For example, Summers made a comment that made me realize that both of my bikes had a slightly lean pilot setting (stock) that caused difficult starting in cooler weather. With that setting, I have to twist the throttle 3-4 times prior to kicking versus the recommended 1-2 times. Before I realized that fact, I was often unable to start a cold bike in cooler weather. I would eventually flood the bike and have to put in a fresh plug to get it to fire.

2. Not sure what you mean by "rough". Make sure you're not referring to a slight stumble which may result if you whack the throttle open too quickly (vs. roll on). This is a common attribute of this bike although they apparently tried to minimize it with the 01 model.

3. Make sure you have not tried to start the bike immediately after oiling the air filter. Not sure why not. I just know that it will fire, cough, die and not restart until I replace the plug.

Sorry for the long post especially if you already know this stuff. However, the stock YZF setup is pretty good. Either you're doing something wrong or it is defective. You should not have to make jetting / pump changes just to get it to run correctly.
 
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#8
Originally posted by drewblue
After it warms up, it is running rough at 1/4 to 3/4 throttle. It also frequently fouling plugs. The main jet has been changed from a 162(stock) to a 150. The dealer also suggested changing the accelerator pump from a 8mm stroke (stock) to a 7mm, which I did.
As mentioned already it could simply be your jetting, you ride in much thinner air at your altitude than most folks for whom stock jetting works fine. If you are fouling plugs due to rich jetting changing the main jet is not the solution.

As for the rough running at ¼ to 3/4, it sounds like you are rich on the clip position, not on your main jet. Try dropping your needle 1 clip (raising the clip). You may also try a 40 pilot (stock is 42), this should make it easier to start and an overly rich pilot is normally associated (in addition to accelerator pump abuse) with fouling plugs due to rich jetting.

I’m curious as to how exactly you shortened the accelerator pump stroke, and where are you making the 8mm measurement?
 
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#9
slowmo:
Thanks for the detailed information. You may be right, I suspect I need to refine my starting technique. I do have a couple of questions. Are you supposed to let the bike idle for any period of time prior to riding (I usually let it idle for about 2 mins)? Also, is it bad to slightly rev the bike after starting it (would this cause plug fouling)? Are you supposed to roll the throttle as compared to snapping?

I really appreciate the input,

Drew
 
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#10
Hick

Hick,
The accelerator pump measurement is simplt the factory measured stroke of a new accelerator pump. This was a replacement part.
 
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#11
Originally posted by drewblue
Hick,
The accelerator pump measurement is simplt the factory measured stroke of a new accelerator pump. This was a replacement part.
Measured where? Did you buy a new pump diaphragm? Which one? Did this help things? I tried to order a few optional diaphragms several months ago and they were not available.

The pump stroke, stock, of my ’01 is nowhere near 7 mm, more like 3 mm, measured at the actuating rod.

Again, at your altitude I would think a leaner needle clip setting is in order to cure the “running rough at 1/4 to 3/4 throttle.”

It is a good idea to let your bike warm up a bit before you ride it. Blipping the throttle can result in a fouled plug especially on a cold bike.
 
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#12
Hick

The measurement is the FULL diameter of the diaphram from one side to the other, not from the accuating rod to one side...
If you can't locate the accelerator pumps at your local dealer, try some nationwide outfits. I had to special order the 7mm and 5mm diaphrams, and they took a little while to arrive. I appreciate your help on the warm up tip.
Good Luck...

By the way, I tried the 5mm pump, it caused a major bog. The 7mm was just installed, and I will test it on Friday....

Drew
 
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#13
Listen to Hick-

Be sure to move the needle clip leaner to #3 position.

The advice to use a 150 main was incorrect, something more like a 158-160.

Try to adjust the pilot screw on the bottom of the float bowl. Turning it out is richer and in is leaner.

What supplier provided the diaphrams with different diameters?? The Sudco catalog only shows one available. :eek:
 
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#14
James Dean

J.D.
Apparently Yamaha has just started offering the new Accel pumps. I had to special order the ones I wanted (5mm and 7mm). As for the 150 main jet, I'll let you know how it works (toady I ride). I have to run a much leaner jet due to the altitude (8,000 - 10,000 ft.). Thanks for the tips.

Rock on!!!
 
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#15
What are the new pump part numbers?

I would like to see these new enhancements for the FCR carb. Sudco didn't know about them. The local Yamaha shop found no references to them. You are my only source! :eek:

Both 5mm & 7mm part numbers please? ;)

Suggest you go with #40 pilot, EJP(stock) needle clip #3 (or #2 if sputtering persists at 1/4 throttle), #152 main. Work to adjust the pilot screw carefully in 1/4 turn increments to get a clean running idle. Again, out is richer and expect to be in the range of 1-2 turns. During a cold startup try to adjust this to feel a slight lag (lean) until warm, at which point the lag/delay goes away.

Thanks,

James