YZ426 mods for offroad


14 replies to this topic
  • Punisher660

Posted June 21, 2006 - 09:46 AM

#1

I recently purchased a YZ426 for my son for a great price. We mostly ride desert/single track. I know the 426 is a track bike, but for the price paid, it was too good to pass up. Here are a few questions:

1. He is only 130 lbs so needless to say he has a hard time putting enough weight behind the kick start and the starting routine seems to be difficult for him. What cam is needed for the auto decompression to work? I have a spare stock cam from a 04 WR450....will this work?

2. The bike seems to be very difficult to start after warming up. Last week, the only way to get it started after a 1hr ride was to bump start it. Any ideas as to the cause of this?

3. The bike seems to overheat easily when doing slow technical offroading.....does anyone make a catch bottle for the antifreeze like on the WR? Will a catch bottle for the WR426 fit it? Did thos even have one?

4. Does anyone have any other mods they recommend for making the YZ426 a more offroad oriented machine?

Thanks in advance.

  • elcamino76

Posted June 21, 2006 - 10:15 AM

#2

not sure if the 04 wr cam will work but i know that everyone puts in a 03 yz cam for the auto decomp. usually the 4 strokes are harder to start when warm, usually with the 426's, once you get down the "drill" for starting you should be alright. not sure about the catch bottle, but the bike probably needs to be geared down for the trails so you are not overheating as much. what are you runnig now??

  • Punisher660

Posted June 21, 2006 - 01:24 PM

#3

The guy we bought it from had it geared pretty low....down 1 tooth in the front and up 2 in the rear.

  • SRT426

Posted June 23, 2006 - 03:02 AM

#4

As far as the starting - make sure you use the hot start when the bike is warm. Depending on how your jetted sometimes you need it and sometimes you don't. With my setup I need it at sea-level but up at about 4000' where I usually ride it starts no problem.

As for off road mods, maybe go up a tooth in the rear to help with a little more grunt on the singltrack. I'm currently running 48 tooth which is great for desert 49 is stock), but it really needs a 50 for the trails i usually ride. It's all personnal preference.

Edit - Just re-read the post and saw your geared pretty low already, maybe since he weighs so little gearing it up a bit may help on the trails so the power is more manageable - Maybe run the 14-48 setup like I have right now.

  • Punisher660

Posted June 23, 2006 - 07:13 AM

#5

Were not really having any power issues, it seems more "trail-ability" issues. We went up the same riding area (2 of us on WR450's) and my son on the YZF -

I will tear into it this weekend to check valve clearances (could be why its hard to start when warm), but the bigger issue we had was overheating.

We pulled a long, slow up-hill, and the WR's were fine, the YZF on the otherhand was spewing coolant all over the place.

I know the 426 was not designed as a "trail" machine, but I have tackled this same hill on a number of 2-stroke MX bikes and a CRF 450 without any problems at all. What could be causing this?

A catch bottle would be great as to not waste all of the fluid, but we were prepared this time and had packed extra fluid with us.....my biggest concern is why its overheating so easily to begin with?

  • kid on a 426

Posted June 23, 2006 - 10:19 AM

#6

I recently purchased a YZ426 for my son for a great price. We mostly ride desert/single track. I know the 426 is a track bike, but for the price paid, it was too good to pass up. Here are a few questions:

1. He is only 130 lbs so needless to say he has a hard time putting enough weight behind the kick start and the starting routine seems to be difficult for him. What cam is needed for the auto decompression to work? I have a spare stock cam from a 04 WR450....will this work?

2. The bike seems to be very difficult to start after warming up. Last week, the only way to get it started after a 1hr ride was to bump start it. Any ideas as to the cause of this?

3. The bike seems to overheat easily when doing slow technical offroading.....does anyone make a catch bottle for the antifreeze like on the WR? Will a catch bottle for the WR426 fit it? Did thos even have one?

4. Does anyone have any other mods they recommend for making the YZ426 a more offroad oriented machine?

Thanks in advance.

1. I think it should but if you want to know for sure ask grayracer.

2. Try the hot start lever or it could be jetted wrong or fuel screw, sparkplug or valve clearances.

3. Well the overheating problem could be a result of lean jetting. But the wr426's did come with a catch tank and it will fit with slight modification to the side panel.

4. Skid plate, Rad guards, geared way low, possibly a trials rear tire(Friend has one on a rm250 and swears by it), suspension, hand guards, maybe a rekluse, and a good set of bars that won't get all bent up.

  • mankind810

Posted June 24, 2006 - 04:55 AM

#7

Check the radiator cap to see if it is sealing properly, if it is not it may be giving you a false indication of over heating.

And check out this guys mods for easier starting and other helpful advice.
http://motoman393.thumpertalk.com/

Hope this helps :excuseme:

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • Fastest1

Posted June 24, 2006 - 07:08 AM

#8

First of all which year 426 is it? The few mods I think will help in order of importance are (1) JD Jetting kit once you install it you will know exactly why I recommend it. Follow his instructions to the letter and you cant go wrong.(2) Power Now, I catch hell in the belief that this product works but it does help immensely on instant/initial throttle, great for low end with no noticeable effect in the upper end, seems to help starting too. (3) the exhaust cam from an 03 YZ, a WR cam will mellow the hit so that might even be better for you. The addition of the auto decomp cam whether from a YZ or WR will help the starting for anyone who rides the bike period. (4) REKLUSE AUTO CLUTCH, for a woods machine it is the killer! You will not be able to stall this bike. Set up is easy, customer service is beyond anything you will experience in this day and age, and he is a TT member first and foremost. I promise should you do these things and you will be amazed at the change. Water wetter will help the heating issues to some extent as would WR radiators or Fluidyne rads, A Boyesen(sp?) water pump cover and impeller couldnt hurt either.

BTW after trying all kinds of jetting, needle and carb mods and tricks, I recently installed the JD Jetting kit just as he instructed and all I can say is WOW. Crisp and precise and barks with authority, I thought it ran great before but I was mistaken. I was already running the 170 main and the 42 pilot but the needle he makes must be the difference and the Oring trick. I ran the BK/GB mod for years and it is a great price mod with good results but nothing like I got with that jetting kit. I turned the BK/GB mod screw out so it doesnt interfere with JD's settings. Sorry to be so long winded but in my pursuit of perfection with the 426, the only thing I desire is lighter weight and a lower CG power is a non issue, there is plenty especially if I was 140, i weight 255.

  • bnio

Posted June 25, 2006 - 08:58 PM

#9

If your son is 130 pounder do the 03 cam swap for auto decomp. Actually if you have the budget it should be done anyway no matter who you are unless you are sadistic and love to punish yourself then leave the manual decomp on. Your choice, I went with the 03 cam and I am glad I did.

  • crashyz426

Posted June 26, 2006 - 02:56 PM

#10

I left the decomp lever on mine and I love it. It just takes an extra second to push it and let up on the kickstarter and kick it. It almost always starts on the first kick hot or cold. I see the guys on TV crash and kick and kick and kick their bikes trying to get them started again. If I crash mine, pull the hot start, starts on the first kick. I tried riding my buddys crf 250 and kicked and kicked before it got started, I know its only a 250 but it just felt like it didnt have any compression... Anyway, after seeing the guys on TV and the announcers saying how hard it is to get them cranked after a fall or crash, Ill keep mine just the way it is.

  • ONLY4STROKES

Posted June 26, 2006 - 03:50 PM

#11

1. If the spare cam from the WR450 is the exhaust one, then yes it will work. If it's the intake cam...don't waste your time because the auto-decomp. feature is only on the exhaust camshaft.

2. Are you using the hot start (sorry, I had to ask)? It could be a few different things. Check the idle as it could have been unknowingly adjusted during the ride. With the recent weather change into summer the jetting may be a bit off, try playing with the fuel screw as well.

3. Yes, the WR426F has a catch tank. I do not know however if it will rig up to the motocross model. I think it can be done though...so after doing that I would reccomend getting a very good coolant and aftermarket water pump. I use ZipTy waterless race coolant and a Boyesen water pump. Although my bike never overheats, I dont want to risk it when I'm racing in 110 degree summer heat.

4. Sure, there are many things. The first mods I make to a motocross bike to make it more friendly off-road is 1) Protection. Definitely make sure you get yourself a good skid plate, or glide plate with case guards, along with a billet shark fin and a tough chain guide. 2) Handguards. You cant really go wrong with bark busters or MX-style shields. 3) Desert tank. I personally like IMS better than Clarke because they put more thought into the design to carry the fuel lower and keeping the handling similar to stock. 4). Steering stabilizer. This mod isn't completely neccesary...but if you live in a rocky area or where there are lots of sand washes...it will become your best friend. 5) Lastly, make sure to get your suspension revalved for off-road and your skill level. It will make you faster than any other mod.

Doug

  • Zique

Posted June 26, 2006 - 09:59 PM

#12

I would agree with everyone that it sounds like your jetting may be off. It is good that you are going to be checking your valve clearances in the near future as well.

As for the mods:

1) Guys here swear by the rekluse. I am not strictly a trailrider, so I have not purchased one, but from what I understand, that is what you want.
2) Get the suspension set up for him
3) BK mod and it sounds like you are already working on the auto-decomp.

I think this is all a good start. Take it piece by piece and he'll have the ultimate trail weapon in no time! :excuseme:

  • srhines67

Posted July 06, 2006 - 08:38 PM

#13

I just put the auto decomp on my 02 426 and it is awesome. Its like riding a totally different bike in the woods. It kicks like a 2 stroke and starts right up.

If I ride really slow I can get my 426 hot and it is jetted fine. I tend to keep moving so this is rarely a problem. I have only had to stop one time and check coolant and I has just lost an ounce or so. I also have my bike geared way down and the suspension set up like Dwight Rudder suggests in the off road forum. That really helps offroad.

  • Punisher660

Posted July 07, 2006 - 08:09 AM

#14

Well I followed all the advice you guys gave me and most of it was spot on. The jetting helped the overheating, the valves were out of spec, after shimming them, it is starting easier now. Unfortunately I think the bike is gone after this season.

We test rode the bike before buying, and it ran well, but after pulling the head to adjust the valves, it looks like the head was installed with a hammer! There were nicks and dings on the inside, and I don't dare install the WR cam. If it were to touch one of the dinged parts, kiss the motor goodbye.

For now my boy can learn to kick a bike like a man.....using the manual decomop will make him really appreaciate a newer machine I guess. I will be on the lookout for a head for a 426 as well, but I appreciate all the responces, your input was valuable.

  • drdanny

Posted August 18, 2006 - 12:40 AM

#15

i ride a 03 yz450f. i also have an 06 400 ktm, before i had a 98 yz400f. on every one i used the catch bottle off of a 1990 kdx 200. fits right under the panel opposite the exhaust and works great.





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