426 Running HOT! Any Advise.

16 replies to this topic
  • hazey123

Posted August 18, 2008 - 08:25 AM


My 2002 WR426 runs hot. I'm not sure if this is normal but I don't think so. I can't ride a slow trail in 1st for too long or it will boil over after a few minutes (80'F air temp. for 5 min). With higher speed riding it will stay around 190-210'F.
I recently replaced coolant with Engine Ice and I don't see a noticable difference.
My left radiator is tweaked a bit with maybe 3 or 4 rows of fins squished out of 12 total but no leaks. Would this have a large enough impact?

  • Bladerunner426

Posted August 21, 2008 - 01:11 PM


A little radiator tweak that size wont hurt you. You should check your Radiator cap and make sure it is sealing. If it isn’t then the water will boil over a lot sooner. Also check your carb and be sure that it isn’t dirty or running lean. Check air fuel mixture screw and jets.

  • Fullbore4

Posted August 21, 2008 - 10:12 PM


yah perhaps a new cap would be a good thing if its boiling below 265-275 deg F which is approaching max for a pressurized system that has a good cap, before boiling out coolant. What are you using to monitor the temp? I have a Vapor and they claim it is accurate. On a hot day (90+), mine runs 175-200 going 25-40 mph but heats up quick doing 1st gear for over a minute or two. I hit 240 last time out doing 10 mph technical stuff, so I shut it off for 15 minutes and let it cool down. However I have a 3.2 gallon IMS tank on it so that doesn't allow as good of cooling behind the radiator. These buggers sure need air flow through the rads!

  • Dee Perry

Posted August 22, 2008 - 05:00 PM


My 2002 ran hot at low speeds also. I rejetted it and have had no problems since. I typically ride in 90+ temps, and follow my wife around in first crawling around on the trails.

  • hazey123

Posted August 22, 2008 - 06:53 PM


I wouldn't last more than a few minutes crawling around in first. What did you end up going with when you rejetted.

  • byggd

Posted August 23, 2008 - 03:59 AM


You could run Evans coolant and some two2cool and I’m sure it would help. Start with the basics and check you radiator cap. If the cap is not the problem then your jetting might be off. What jets are you running now and at what altitude do you ride?

  • hazey123

Posted August 23, 2008 - 10:29 AM


The previous owner put in 170 main, the needle clip at 3, and a 42 pilot. I think, only because I found his notes in the manual. I also just found that the pilot screw is MISSING! I ride at 2000 ft with mild temps 70-80'F. THanks for any advise.

  • byggd

Posted August 24, 2008 - 05:04 AM


pilot screw is MISSING

I think you found the problem :thumbsup: Pick up one of these. You will also need the little washer and o-ring that go on the tip.


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  • hazey123

Posted August 24, 2008 - 04:28 PM


Would the missing pilot screw cause the high temp issues? Would it cause a lean condition?

  • byggd

Posted August 25, 2008 - 04:07 AM


The pilot screw is a fuel screw (meaning the farther out it is the richer the mixture) so I'm not 100% sure what would happen if it was missing but i would think it would suck air and cause a lean condition. I guess there is a chance it could cause a rich condition too and this too can make a bike run hot. Have you taken it on a good run and pulled the plug to read it?

  • Mosow

Posted August 25, 2008 - 05:34 AM


Also check your header pipe and make sure it is not touching the radiator.

  • hazey123

Posted August 26, 2008 - 10:05 AM


I haven't pulled the plug to do a color check. I should it's just a pain from what I can tell with the Clark aftermarket tank hanging in the way.
The header pipe isn't in contact with the rad but it is in close proximatey by design.

  • drtbk4ever

Posted August 26, 2008 - 01:30 PM


Would the missing pilot screw cause the high temp issues? Would it cause a lean condition?

This should be a major "Doh" moment. There is no way to properly diagnose your issues until you get a new fuel screw.

So get on it.

  • hazey123

Posted August 26, 2008 - 05:58 PM


Working on it. It'll be here tomorrow.

  • byggd

Posted August 27, 2008 - 01:49 PM


I should it's just a pain from what I can tell with the Clark aftermarket tank hanging in the way.

It's a pain with a stock tank. :worthy: Both seat and tank must be removed and then you need just the right tool set up.

Let us know how it turns out! :thumbsup:

  • hazey123

Posted September 01, 2008 - 05:17 AM


I got the new pilot fuel screw, Moose Zypty Screw complete set with oring, spring and washer. I installed it on Saturday and rode 70+ miles of trails yesterday. MUCH MUCH better. I didn't over heat once even on the tight technical stuff. It does still run a bit hot but nothing like before.
I'm thinking it must have been suckin air by the missing screw causing a lean/hot condition.
Thanks everyone for your awesome feedback.

  • byggd

Posted September 01, 2008 - 06:33 AM


It does still run a bit hot but nothing like before.

That's normal. These big thumpers put out a lot of heat! Glad to hear you're back on the trails! :thumbsup:


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