Question about 2004 Yamaha YZ 450 F

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My 2003 yamaha yz 450 is impossible to start cold. I've been kicking it for 20 minutes. Finally got it started, rode it down the street and back ion the garage, and now it won't start again. When it's hot it is great, but the initial startup is a pain. Help

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  • jason_pollia Sep 17, 2010

    cool. Thank you

  • Anonymous Mar 20, 2014

    I lived at the coast and moved up to about 4500ft. same problem



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Have you had your valves adjusted?

Posted on Sep 16, 2010

  • 1 more comment 
  • jason_pollia Sep 16, 2010

    they are exactly on spec as per the book. The bike has always had a problem cold starting. Thought maybe I was just going through the process wrong or something

  • cheap repair Sep 17, 2010

    if compression is good, and spark is good ( does it have a good plug, properly gapped?) then I would think the carb is clogged up.

  • cheap repair Sep 17, 2010



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Hi, i just got a 2003 yz450f and theres a black "trigger" right next to the clutch on the handle bars. Is it the choke? because i've held it down and tried to start the bike but it backfired...


Jul 13, 2011 | 2003 Yamaha YZ 450 F

1 Answer

My 2003 yamaha yz450f will not start when it is hot. Why? What is the compression supossed to be? Could jetting cause the problem. It will start and idle when cold, but once it gets warm/hot it will not...

OK a cold starting YZ
yes you have nailed one cause but is unlikely if runs well until you switch off then cant restart but if you don't even get to ride for a while then I would not necesarily be re jeting but cleaning the jets and or replacing same size jets would be great place to start
the most common issue or maintenance is valve clearances and although they should not need to be adjusted to often they give you awefull starting problems if they are out of spec
and being the age of the bike I would consider getting leak down test done to varify the vales are in good shape and sealing well
Compression test of any use on your bike would be impossible as the auto decompression would hinder any results but if you could get past that issue then anything over 200 psi is good and will run fine on less but we all want the best so aim high I say

Nov 23, 2010 | 2003 Yamaha YZ 450 F

1 Answer

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1. First thing is when was the last time you had your valves adjusted
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My YZ 450 dirt bike seems almost impossible to crank. What is the problem??

In my experience, 90% of the time, just regular hard starting is an indication of needing your valves shimmed. Those bikes can be very hard to start and flood easily, very frustrating. Valves are supposed to be shimmed every 15 hours. If you are just having problems kicking it over in the first place you quickly need to have your cams checked. Your exhaust cam has an auto-decompression spring and weight on it to help ease in kicking it over. Having that come apart can be catastrophic if not checked in a hurry...

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YZ 125 kick starter doesn't spring back

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Sep 03, 2009 | 2003 Yamaha YZ 250 F

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'03 450 always seems cold-

Do a compression check. It should be 120lbs or above. Check the compression release. Is it closing fully? Burned valves may be at play here also. Bad piston rings or seize scars on the cylinder wall? If you need a service manual you can download a free PDF from the site below.

Please rate this answer. Thanks ellismd79!

Apr 20, 2009 | 2003 Yamaha YZ 450 F

1 Answer

Engine dies, starts right back up then dies, now won't start

Springtime start ups after sitting up for awhile can be a problem. You have nothing to loose, spray some starting fluid into the air cleaner. That may be just what is needed for an easier spring start.

Apr 05, 2009 | 2003 Yamaha YZ 250

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Very hard to start after the engine is hot

I had this problem before. Here a quick glimpse of what could have been the problem:

Fuel is is filled into the carburetor by the float switch. Starting from cold, its just normal that the carburetor is up and ready for a start. As you cruise along, the carburator is filled up with fuel coming from the fuel tank and is regulated by the float switch. Now, if the engine consumes more fuel than the rate of flow by the float switch, then it will drain the carburetor fuel reservoir empty. What could be the cause? You guessed it right... dirty jets or clogged fuel jet on the float switch. Solution: Open up the carb, clean every hole with wire brush. Blow compressed air on the needles and every hole you could see.. Take not of the ball bearings inside make sure there isnt anything loose when blowing with compresssed air.

Assemble the carb back and cruise for 20 minutes.

Other cases: dirty spark plugs, missfiring plugs, or worse case, CDI ..

Let me know if this helps.

Mar 17, 2009 | 2003 Yamaha YZ 450 F

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