426 overheating


14 replies to this topic
  • kjwarren

Posted October 26, 2009 - 02:24 PM

#1

Took my 426 to the dunes. About half way through the day it started idling high and overheating. Any ideas?

  • grayracer513

Posted October 26, 2009 - 02:38 PM

#2

How does it run now?

  • kjwarren

Posted October 26, 2009 - 03:01 PM

#3

Seems to be running fine I havent riddin it since but I started it in the garage and seemed to be running fine.

  • buzzgrizz

Posted October 26, 2009 - 03:35 PM

#4

Not sure what the problem is but when my 426 was giving me overheating issues I installed a Boyesen water pump no overheating issues since. :bonk:

  • phart2005

Posted October 26, 2009 - 03:42 PM

#5

High idle and overheat are symptoms of a vacuum leak. Start it up and spray carb cleaner around the flanges and carb and anywhere else that would be exposed to vacuum. When the engine starts to sputter, you found the leak.

Of course use care with the fire hazards involved with spraying carb cleaner.

  • kjwarren

Posted October 26, 2009 - 03:50 PM

#6

what else can be exposed to vacuum

  • phart2005

Posted October 26, 2009 - 04:15 PM

#7

Take the Black 'Kehin' cover off the carb where the cables go in. Odd are its full of dirt there and need to be cleaned anyhow. Spray it. It can leak right there where the shaft for the throttle valve linkage is.

Where the airbox attaches, there is a plastic flange, that has an o-ring to seal that flange to the carb body. Spray around there.

Hot start knob could be leaking around its seals also.

Thats about all I can come up with right now.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • phart2005

Posted October 26, 2009 - 04:18 PM

#8

Also, pull the carb off if you are confident in doing so. Take the cover off the top. If its full of dirt, its leaking air at the shaft seal.

  • kjwarren

Posted October 26, 2009 - 04:43 PM

#9

Ok thanks. Another thing when I adjust the the fuel mixture screw it takes a while for it to adjust

  • phart2005

Posted October 26, 2009 - 04:47 PM

#10

When idling, can you bilp the throttle, and does it hang a bit when slowing down? Would you say that the idle is erratic?

If so on either of these, it is vacuum leak for sure.

  • kjwarren

Posted October 26, 2009 - 05:01 PM

#11

the idle isnt erratic its just a little high when it was over heating it seems fine now ill try what you said tho just to see if it makes any difference.

  • grayracer513

Posted October 26, 2009 - 06:26 PM

#12

the idle isnt erratic its just a little high when it was over heating it seems fine now ill try what you said tho just to see if it makes any difference.

What where the symptoms of it over heating? The circumstances?

  • kjwarren

Posted October 26, 2009 - 07:26 PM

#13

A lot of coolant started shooting out of the overflow and the idle was high, and motor was really hot. It was about 100deg that day and we were going pretty slow through the dunes so there wasnt getting much air through the radiator so I figured it was overheating. Just did a full motor rebulid on and this was pretty much the first ride after break in. I did flip the bike forward while going down a dune could have something to do with it?

  • grayracer513

Posted October 26, 2009 - 08:12 PM

#14

I doubt it. More probably just an heat issue. The only thing you can do about it now is to check it over to make sure it's OK, and check the valve clearances to be sure they don't have anything to do with the hanging idle.

  • kjwarren

Posted October 27, 2009 - 10:10 AM

#15

valves were checked before the dune ride and they were good should i do them again?





Related Content

Forums
Photo

2016 YZ450 by CaptainKnobby


Dirt Bike   Dirt Bike Technical Forums   Suspension
  • Hot  59 replies
Reviews

Yamaha YZ450F 2017 by Chris.GVS


Yamaha YZ450F 2017
  • - - - - -
  • 0 reviews
Forums
Photo

Megabomb Fitment by 288yz450


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 1 reply
Forums
Photo

YZ450F 03 Sparks driving me crazy by SirAttard


Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 5 replies
Wiki
WR Camshaft Swap Info - last post by jamesm113

WR Camshaft Swap Info


Articles
  • 0 replies
 
x

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.