2007 yz450 hard cold start

7 replies to this topic
  • motorcross242

Posted May 15, 2012 - 08:16 AM


I have been having a hard time starting my bike. My jetting is stock and I'm at about 800 ft above sea level. I've replaced main jet, pilot jet. I've tried the whole, twist the throttle a few times then kick.

What seems to work the best and easiest is to pull in the hot start lever. Usually the bike will kick right over. I notice very little difference whether the choke is on or off.

What could be causing this? It would seem the hot start is leaning out the mixture? The fuel screw is 1-1/2 turns out.

  • 559stan

Posted May 15, 2012 - 04:04 PM


I have the same year yz and it takes 7 or so kicks when cold and makes me wish for a ktm. Hey i'm old

  • grayracer513

Posted May 15, 2012 - 06:00 PM


With my '06, any time the temperature is below 80, it wants a good healthy prime to cold start. I turn the gas on, wait for the bowl to fill, twist 2-3 times, then push it through to the next compression stroke (the "hard spot"). Then I twist it 2-4 more times and kick it with no throttle. If it doesn't start, I give it another couple of twists and try again. Normally, that does the job. If it hasn't started in 3 tries, I'll either push the hot start or crack the throttle just over an idle to get it going before priming again.

Out of curiosity, what size pilot are you running?

  • motorcross242

Posted May 15, 2012 - 06:32 PM


Pilot Jet is the stock #45. Replaced with new OEM recently. Starter/Leak jet have never been replaced.

Mr. Grayracer,

Just to clarify -

1. Turn gas on wait 'til the bowl is filled.
2. Twist throttle 2-3 times, find compression stroke
3. Twist throttle 2-4 times and then kick with no throttle
4. If it doesn't start twist 2-4 more times, kick again with no throttle
5. If it still doesn't start twist 2-4 more times, kick with no throttle
6a. If it still doesn't start you'll pull/push hot start while kicking? Letting go, once bike starts and rev's - This is what makes my bike fire first kick
6b. You'll crack the throttle slightly while kicking? - Just clarifying, because I've done this and the bike will fire up.
7. If it still doesn't start, you start the process all over again?

I understand this is pretty redundant that I'm confirming this information, but I just want to make sure what I'm doing is safe.

Edited by motorcross242, May 15, 2012 - 06:33 PM.

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  • grayracer513

Posted May 16, 2012 - 06:51 AM


Yes, that's how mine works.

You say yours will cold start with the hot start first or second try most of the time? And you are saying that the choke doesn't seem to matter? What happens when you pull the choke while the engine is running?

Does the bike pop at all on decel?

  • motorcross242

Posted May 16, 2012 - 07:07 AM


Yes, my bike will cold start within the first few kicks with the hot start pulled in. The choke does not seem to change the RPM's very much, it's a slight difference, as I have a tach/hour meter on the bike.

I have never purposely pulled the choke out while the bike was warmed up, I will report the rpm difference tonight after work.

At the track this last weekend, the bike does pop a little on decel now that my fuel screw is 1-1/2 turns out, it had no popping on decel at around 2 turns out.

Being that the starter jet is used when the choke is pulled out, is it a good idea to replace that? Can it be accessed through the drain plug on the bottom of the carb?

  • grayracer513

Posted May 16, 2012 - 10:13 AM


The starter jet is not so easy to extract from the bottom plug unless you have the carb off the bike (don't tell me, I know that's a PITA) because you have to angle over to it some. I don't generally find a reason to replace most jets. I usually clean them either by picking the orifice clean with fine brass wire, or by passing a correctly sized number drill through them. The original '07 starter jet is a #72, which is .72mm or .0283". A #70 drill is .71mm (.028") and will clean that jet nicely.

Number drill chart

  • td400F

Posted May 16, 2014 - 04:47 PM


my 98 400f revs up on idle when i pull hot start and is a BEAR to start cold im in oak creek WI 

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