Wr426 Engine Upgrades


7 replies to this topic
  • BOULMAN

Posted March 14, 2007 - 04:52 AM

#1

I have an 02 dual sported wr426. Runs great! No problems, but I am thinking about making some changes after this riding season. I want a liitle more power for the sand, but don't want to lose any reliability.

Upgrade valves?
Cams?
Big Bore kit?

Who does good engine work? Is it still a good trail bike with the bike bore kit? How reliable is it? Start easy still?
Do I need to upgrade exhuast to make all of this work right or is just my changed insert ok (Sound and spark arrestor)?
Any experience you guys have with the above would be great.

Thanks

  • Birdy426

Posted March 14, 2007 - 08:16 PM

#2

I have an 01 WR426 (also DS's and plated). When I rebuilt it, I stuck with the stock Ti valves and springs. They are bullet proof. Some folks will say KW are the way to go, but I'm not all that comfortable with the heavier valves and stiffer springs (concerns about beting up the valve seats).

My engine mods include a Luke's Racing 444cc kit, Hot Cams intake and exhaust cams (with auto-decomp), Wiseco 13.5:1 piston, Eric Gorr porting, JD jet kit, Power Now, Quickshot, and a YZF pipe with a PMB quiet insert. The power is very WR like down low (just a lot more of it), with a YZ-like midrange hit and a poop-load more overrev than either the YZFs or WRs. I went up one tooth on the countershaft sprocket, and could probably go up one more and still have more than enough bottom to pull it. As far as reliability, I've got about 1800 desert miles on the rebuild, with absolutely no problems. I change the oil and filter after every day of riding, so I expect pretty long life...

Engine work...hhhmmmm...I've had exceptionally good service from Eric Gorr's forward motion (google to find him). You have to ship your stuff, but he is good. Engine Dynamics up north also has a good rep. Obviously in SoCal, Pro Circuit will treat you right, for a price, and George at ESP is fan-frickin'-tastic and stands behind his work.

As far as starting, there are two issues...First, the high comp and increased displacement require a significantly harder kick to rotate it fast enough to light off. I have really short legs, so if I don't have a block, rock, or berm to stand on, it can be kinda tough to get enough of a kick to start it. The second issue is cold starting. It's just plain hard. I'm continuing to fart around with pilot jets, fuel screw settings, and needle positions, but I haven't found the holy grail yet.

Where in Cali are you?

  • BOULMAN

Posted March 14, 2007 - 09:38 PM

#3

Thanks for the info. I was sold on changin the valves after reading Eric's website, but maybe I will not. I am just looking for a liitle more power to pull a paddle if I decide to get one. It is great as it is for trails and desert.
It starts really easy now hot or cold. I guess harder starting is the down side to more power.
I live in central ca in the hills.

jb

  • Birdy426

Posted March 15, 2007 - 06:10 AM

#4

Before I went big bore, I was running a 13.5:1 std bore and did not have the same starting issues. Fair bump in power as well. I went big on the bore when the cylinder finally went outside of limits. It cost about the same as a new cylinder and piston kit, and, afterall there is no replacement for displacement.

I thought lng and hard about valve choice when I did the rebuild. Lots of folks really like the Kibblewhite valves, includingh Eric Gorr, but ultimately, I got about 7000 miles out of my stock Ti valves, and 4 of the 5 were still perfect at rebuild. At the time I did mine, KW was having some supply problems (the whole world was out of stock) and the DRZ guys were having some reliability issues as well, so I went with what I knew worked well.

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  • ryder

Posted March 15, 2007 - 06:22 PM

#5

Birdy426,

that is interesting that you found it hard to start after the big bore, by chance was that also the same time you put the intake cam in?

I have a wr400, that I had eric gorr turn into a 420.
I put a stock auto decompression exhaust cam and a hot cams intake cam.

Cold starting can be a pain for me also. I am thinking it is the intake cam that makes the starting difficult.

Just some thoughts

  • Birdy426

Posted March 15, 2007 - 07:28 PM

#6

Birdy426,

that is interesting that you found it hard to start after the big bore, by chance was that also the same time you put the intake cam in?

I have a wr400, that I had eric gorr turn into a 420.
I put a stock auto decompression exhaust cam and a hot cams intake cam.

Cold starting can be a pain for me also. I am thinking it is the intake cam that makes the starting difficult.

Just some thoughts


No, it wasn't when I put the cams in. I had both Hot Cams and 13.5 to 1 piston installed on the stock bore, and it started first or second kick EVERY time, hot or cold. I keep diddling with the routine (choke, no choke, give it a squirt and hold the throttle closed, no squirt and hold the throttle closed, whiskey throttle, kick it through slowly a couple of times, wave a gri-gri bag and chicken bones over it, etc), pilot jet, fuel screw, and needle jet clip position (and even switching from blue to red and back with the JD jet kit) hoping to make it better, but I really believe my short legs just don't get me enough leverage on the kicker when it's cold and hardest to start.

  • BOULMAN

Posted March 15, 2007 - 10:00 PM

#7

What about exhaust. I have stock exhaust with an aftermarket insert. I just wonder if I need to upgrade exhaust with the big bore kit.

  • Birdy426

Posted March 15, 2007 - 11:20 PM

#8

What about exhaust. I have stock exhaust with an aftermarket insert. I just wonder if I need to upgrade exhaust with the big bore kit.


I'm running a stock YZF exhaust (makes a huge improvement and saves several pounds over the stock WR exhaust...plus, it was cheap!) with a PMB end cap and quiet inster. Seems to work great.




 
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