Is there a technique to easily start a 13 yz450f?

13 replies to this topic
  • colerlone

Posted April 07, 2016 - 06:31 PM


It's never real hard, but when it's cold it usually takes a few kicks if it's cold out. If i kill it, i hold the throttle wide open and slowly kick it twice then release n it usually starts right up. Any pointers? Should i kick slow or fast? I try to get it to tdc before i kick it, but i never know which stroke im on

  • grayracer513

Posted April 07, 2016 - 07:28 PM


By trying to locate actual TDC, you're both over-thinking and defeating the automatic decompression system.  TDC actually has nothing to do with it.


With the old manual decompression YZF's, the plan was to turn the engine until you hit compression; the hard spot.  Then, you'd pull the compression release and advance the crank, but only so far.  Just an inch or two, then let go the release, reset the kick starter and kick. 


Now, with the old British bikes old timers like me learned on, the idea was to use the decompressor to actually go past Top Dead Center (TDC) so that you could then jump way up off the saddle in a nice smooth arc and ram the engine through just under two full revolutions, by which time the engine would be turning fast enough for the massive crankshaft to carry it through the following compression stroke and start (probably).


Not done like that now, but that's where all the chatter about TDC came from.  That doesn't work anymore, mostly because the bikes are running higher compression, the rings seal better, and the crank doesn't weigh anything.  Using the old school technique would just result in being stopped cold by the next compression stroke.  With manual decomp on the 426, the intent was to move closer to TDC, but not past it.  That way, the compression stroke was shortened enough that normal human beings could force the engine through the rest of compression and past the ignition point and start. 


The auto decompresssion system works by delaying the closing of one exhaust valve from somewhere around 120 degrees before TDC to about 20-25 degrees BTDC, drastically shortening the compression stroke, and putting the engine in the best position to start from, same as the manual technique is supposed to do.  Any farther than that and you'll pass the ignition point and waste a kick, so push the crank until you hit compression, then stop there.  Reset the starter lever and give a smooth, forceful kick through the entire stroke.

  • Thumbster21

Posted April 07, 2016 - 07:57 PM


"Any farther than that and you'll pass the ignition point and waste a kick, so push the crank until you hit compression, then stop there. "

Stupid question of the day here.....

Is it always on the compression stroke when you start to feel the resistance? I keep reading to kick on the compression stroke which implies that there's resistance on the exhaust stroke also but I can never tell which stroke it is on.

  • grayracer513

Posted April 07, 2016 - 09:05 PM


There's no resistance on the exhaust stroke; the exhaust valves are open. 


If you push slowly through the compression stroke, you'll eventually get to TDC, where it will "pop over center".  It does that because right at the top, there are about 5 degrees of rotation that barely move the piston. At this point, you're on the power stroke, but there's no power.  There is resistance here because all the valves are closed and you're now creating a vacuum by moving the piston.  But you can't confuse the two, really.  If the crank turns freely, it's somewhere in either the exhaust or intake stroke, and the first thing it will hit is compression.  When it does that, raise the lever back up and start it right from there.

  • colerlone

Posted April 08, 2016 - 03:05 AM


Ok, I'll give it a shot today. My 08 was so easy to start, usually first slow kick even when it was warm. I wasn't sure if the efi changes anything, since it's basically turned off unless the enigine is spinning

  • mxracer384

Posted April 08, 2016 - 03:48 AM


I have a 13 and I saw somewhere that you are not supposed to give it any throttle to start it. When it's cold I give it 2 or 3 medium effort kicks and it starts. Maybe try some different fuel maps... I have heard and expierenced that the higher performance maps are harder to start(generally). I run the woods or smooth gradual maps and they start with no effort when warm and cold. Hot is a whole other beast. But I never have to kick my bike hard (partially because I am so short). But solid medium or slow kicks and my bike comes to life in one kick when it's warm.

  • cpetz24

Posted April 08, 2016 - 07:58 AM


My procedure on my 2011 is as follows for the different situations:  There's no real science behind this, it's just what I've found works the best through trial and error. 


If you stall it in a corner or at a complete stop kill the motor:

Get it in neutral, find the resistance, (TDC), reset the kick starter, and one good solid kick.   Trying to start in gear from a dead stop usually does not work, as there is too much drag on the clutch plates, unless you have a brand new clutch that is in perfect working order, then you may have some luck.  


If you stall it and are able to pull in the clutch and keep rolling: 

Keep holding in the clutch to keep the plates dis engaged and spinning, find the resistance, (TDC), reset the kick starter, and one good solid kick.


For dead engine starts to a race: 

Start the bike in neutral just before the board drops, (30-40 seconds before) put the bike in gear, keep holding the clutch in and don't let go,  let the bike come to idle, then hit the kill switch, keep holding in the clutch, then rock the bike back and forth while you're waiting for the 10 second board to keep the plates free, just before the board drops find the resistance (TDC) and when the board drops one good solid kick and go.  Do not hammer the throttle as you are kicking, you have to give it a slight delay to let the motor come up before you send the fuel to it.  That will take practice.  I usually start in 1st gear on dead engine starts as it seems to let the bike fire better.  


The worst thing I've found is to panic and go to just kicking and kicking the bike.  1. 9/10 the bike will not fire up, 2. You wear yourself out.   Just stay calm, follow the procedure and trust me you will loose much less time, and you're heart rate wont skyrocket.  

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  • colerlone

Posted April 08, 2016 - 08:16 AM


I don't race so i try to always start in neutral. I really wonder if it's because the temperature has been cold, it's been below 45

  • grayracer513

Posted April 08, 2016 - 08:51 AM


That can negatively affect hot starts because at those low ambient temperatures with no thermostat, the coolant temp often stays so low that the bike never gets out of the cold enrichment mode, and you can be running an excessively rich mix into the hot cylinder. 

  • cpetz24

Posted April 08, 2016 - 11:48 AM


Have you checked you're valves recently?  Could be tight valves also.  May be good to run a feeler gauge and check once.  Tight valves will make starting more difficult, especially once the bike gets hot.  


I ran all winter in roughly 30-50 degrees, and had no real issues with starting.  

  • colerlone

Posted April 08, 2016 - 12:08 PM


I'll check it out, it starts way easier when the engine is warm

  • colerlone

Posted April 09, 2016 - 03:51 PM


I've been holding the throttle wide open, kick it twice, release it, and it starts right up on the next kick. Is that because it has to energize the efi?

  • WouldsAssassin

Posted April 09, 2016 - 06:23 PM


When cold there is a condensor that needs to be charged and will take a couple kicks to do so. Once it is running the condensor stays charged so it doesn't need additional kicks to charge. What you're doing is the "clearing" procedure. By holding the throttle open you are telling the ECU to cut power to the injector and not squirt fuel in the engine so that all the unburned fuel can be cleared out of the combustion chamber. I've found that sometimes holding a little throttle open or rolling the throttle open MAY make hot starting easier. No guarantees though as sometimes a half assed kick will start it up and others a perfectly timed and executed kick will do nothing at all. The most tempermental and inconsistant starting bike I've ever had. I've learned to only stall it on downhills.

  • colerlone

Posted April 11, 2016 - 12:38 PM


Any idea how long it stays charged? Occssionally it will start first kick but most of the time it is 3. I take a lot of breaks

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