08 yz450 runs like crap at first


29 replies to this topic
  • 95kawi

Posted December 19, 2011 - 08:33 AM

#1

I have a 08 yz 450 I can get it started when cold let it warm up for about a minute then try to take off its really hard and It wants to just shut off as soon as I get going and it heats up alittle it's fine any ideas? Also this bike is bone stock what could I do to make it alittle more responsive Or (better)? Thanks in advance

  • Krannie McKranface

Posted December 19, 2011 - 08:57 AM

#2

I have a 08 yz 450 I can get it started when cold let it warm up for about a minute then try to take off its really hard and It wants to just shut off as soon as I get going and it heats up alittle it's fine any ideas? Also this bike is bone stock what could I do to make it alittle more responsive Or (better)? Thanks in advance


You need to service the carb:

- replace the pilot jet
- replace the accelerator pump diaphragm
- check the pump squirt nozzle for clogs
- clean the hot start plunger to remove any corrosion

  • 95kawi

Posted December 19, 2011 - 09:22 AM

#3

Only thing I know how to do
Is the pilot jet lol just replace it with stock size? Should I do anything with the other jets? Thanks for the reply

  • 95kawi

Posted December 19, 2011 - 09:24 AM

#4

Should I let the carb sit gas overnight?

  • Family Man

Posted December 19, 2011 - 10:49 AM

#5

probley the valves.

  • Family Man

Posted December 19, 2011 - 10:50 AM

#6

how much compression do you feel at the kickstarter?

  • 95kawi

Posted December 19, 2011 - 11:16 AM

#7

Alot of compression just like when I got it

  • 2grimjim

Posted December 19, 2011 - 11:20 AM

#8

How long are you letting the bike warm up for before you try to ride it?

Of course it's going to run like crap if you are only letting it warm up for 30 seconds to a minute before you try to ride it.

3 to 5 minutes warmup is probably the minimum time before you ride your bike. The bike should run long enough that the top tanks on the radiators are HOT before you ride. Not letting the bike warmup properly can cause majoe damage to the piston, cam journals, crank bearings, and more.

  • 2grimjim

Posted December 19, 2011 - 11:22 AM

#9

You need to service the carb:

- replace the pilot jet
- replace the accelerator pump diaphragm
- check the pump squirt nozzle for clogs
- clean the hot start plunger to remove any corrosion


No, he needs to let the bike warm up before he rides it.

  • 95kawi

Posted December 19, 2011 - 11:26 AM

#10

Yea I only let it warm
Up about a minute minute and a half I give it alittle throttle to help warm it up this is the first time it's done it to me I'm new to four strokes sorry

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  • 2grimjim

Posted December 19, 2011 - 11:31 AM

#11

Yea I only let it warm
Up about a minute minute and a half I give it alittle throttle to help warm it up this is the first time it's done it to me I'm new to four strokes sorry


Forgiven. If you have only ridden two strokes before this bike I totally understand.

Since this bike is new to you (and 4 strokes as well) take some time and learn how to do proper maintainance from this website and some of the pecularities of owning/riding a 4 stroke.

Good luck!

  • 95kawi

Posted December 19, 2011 - 11:37 AM

#12

Forgiven. If you have only ridden two strokes before this bike I totally understand.

Since this bike is new to you (and 4 strokes as well) take some time and learn how to do proper maintainance from this website and some of the pecularities of owning/riding a 4 stroke.

Good luck!


Thanks I appreciate it I'm just nervous about every little thing on this bike lol

  • grayracer513

Posted December 19, 2011 - 11:57 AM

#13

The poor running condition you describe is due to the bike running lean at idle and off idle. That may very well be a simple matter of you needing to warm it up more as stated earlier, or it might actually be running lean.

Review the process for adjusting the idle mixture (pilot circuit), then read how the results of that adjustment can be used to determine if the pilot is the right size. If it comes out indicating an undersize pilot jet, bear in mind that that can be caused by even a very thin varnish deposit within the jet. The jet itself may be the right size, but partly clogged. Low outdoor air temps will aggravate these kinds of problems, too.

http://www.thumperfa.../jetting.htm#PJ
http://www.thumperta...ad.php?t=696672
http://www.thumperta...ad.php?t=327405

http://www.thumperta...726#post8021726

  • sacfelix

Posted December 19, 2011 - 12:09 PM

#14

Where in Cali do you live 95Kawi? I live in Antelope, Ca and if your close by you can swing through and we can diagnose it with you getting the hands on. LMK!

  • Krannie McKranface

Posted December 19, 2011 - 12:57 PM

#15

Yea I only let it warm
Up about a minute minute and a half I give it alittle throttle to help warm it up this is the first time it's done it to me I'm new to four strokes sorry


Do you best to give it NO THROTTLE while warming up. Raise the idle, use the choke, what ever, but blipping the throttle on a cold engine (or worse, wringing it out) is how you wear out a motor in nothing flat.

Get it running, let it idle till you can't touch the tops of the radiators, ride slow for 1 min, then go.

Don't do what these mouth-breathers do.....



  • 95kawi

Posted December 19, 2011 - 01:01 PM

#16

Will do thanks everyone

  • 95kawi

Posted December 20, 2011 - 08:26 AM

#17

What jetting do I use for this bike with a yoshi rs2 slip on ?

  • grayracer513

Posted December 20, 2011 - 08:38 AM

#18

Look at the Jetting Sticky to see what others have used on similar set ups.

Top of the forum index.

  • 95kawi

Posted December 21, 2011 - 08:28 AM

#19

That helped thanks one last question I was reading that the 08 head pipe is to big because it was made for that restrictive muffler would it be smart to just get a slip on or spend a couple hundred more and get the whole system?

  • grayracer513

Posted December 21, 2011 - 09:08 AM

#20

That depends on what you want from it. A full system will produce better results, but the difference between a good slip-on and a well tuned system will be smaller than the change you get from getting "shorty" off the bike. The best values in full systems I know of are the DRD stainless, or the MRD systems, but do your own shopping. A used OEM setup from an '06 or '07 is a huge improvement, too.

By just changing the muffler, you'll gain a big chunk of the missing mid range, but you can actually drop 1-2% off the top. Fixing the header issue with a full pipe will usually keep the top end power intact while cranking up the middle.





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