Yz426f being a female dog


103 replies to this topic
  • Arizo

Posted November 17, 2013 - 08:37 AM

#21

I will post, so ppl know what was the issue, after putting my cleaned carb back on. It starts after 5-6 kicks

  • RoosterJ

Posted November 17, 2013 - 07:33 PM

#22

I will post, so ppl know what was the issue, after putting my cleaned carb back on. It starts after 5-6 kicks

Thats great, after spending a few days on mine that i thought was a 450, i am yet to get it to fire up, pilots like to plug from setting up with the fuel of today, i checked my valve clearance and shimmed, the intakes were not off far, if i had known this was a 426 i might have scrapped it ! Dead give away was compression release ! I was trying to time like 450 ? Duh ! Been all a round on pilot and start jet, maybe if i retime and figure out the " Starting drill " this thing might kick start. One could always carry a quad to pull start it when ready to ride ???? 


Edited by RoosterJ, November 17, 2013 - 07:38 PM.


  • yellow ketchup

Posted November 17, 2013 - 07:44 PM

#23

426's definitely need a secret handshake to start. .. choke on. ..pull compression release lever, slowly depress the kick starter until you reach top-dead-center. . Release compression release lever... kick with all your grit. .. if it doesn't fire on that kick, repeat the process

  • Arizo

Posted November 18, 2013 - 12:42 AM

#24

Yes use the drill that Yellow Ketchup explained, but you need to bring the kick start lever about an inch past TDC then bring it up without compression lever.

Why you wanna scrap a 426? There awesome bikes, and if you really have a hard time getting it started you can buy an autodecompression exhaust cam.

You want to retime it? Get it to TDC on compression stroke and look if the marks on the cams line up.

If you din't get it started once and you know the drill.

start in the begin.
spark?
Fuel?
Air?
Timing?
Valve clearance?
Etc

Hopefully my information is a bit usefull

  • grayracer513

Posted November 18, 2013 - 07:35 AM

#25

Yes use the drill that Yellow Ketchup explained, but you need to bring the kick start lever about an inch past TDC then bring it up without compression lever.

 

HELLO... It's NOT TDC.  It's the start of the compression stroke, which is a good 110 degrees before TDC at least.  Turn the engine until you get to the "hard spot" (start of compression), then pull the release and advance the kick starter about one inch farther.  The release the decompression lever, reset the starter, and kick.

 

http://www.yamaha-mo...troke_vid_a.mpg

 

http://www.yamaha-mo...troke_vid_b.mpg



  • Arizo

Posted November 18, 2013 - 09:10 AM

#26

I thought the hard spot was TDC. My mistake

  • grayracer513

Posted November 18, 2013 - 10:10 AM

#27

No, it's not, and you're not the only one who misuses the term in this way.  But the instruction to locate and pass TDC seriously confuses people who actually know what top dead center (TDC) means, which leads them to use the wrong technique, and then of course, the bike is difficult, if not impossible, to start.



  • Arizo

Posted November 19, 2013 - 05:41 AM

#28

I should have known, if you turn the crank to TDC for checking the valves its not the hard spot.

My bike still won't start like it should, but runs good and has tons of power. But it won't idle if i put choke off after 2min riding.

Main jet:172
pilot jet:48
Jet needle: obdqr 4th clip
mixture screw: 2 turns out
Idle screw: 1,5-2 turns
Air filter: twin air
Exhaust: leovinci x3

Any idea?


  • grayracer513

Posted November 19, 2013 - 07:33 AM

#29

 it won't idle if i put choke off after 2min riding.

 

That indicates that there is an internal problem with the pilot circuit.  The pilot jet can appear open, and you can even see carb spray pass through it, but if it has as much as a .02 mm film of dry varnish in the orifice, your #48 jet will act as if it were about a #40 instead.  Varnish can also build in the passageway that runs up into the throat of the carb from the jet and the fuel screw.

 

http://www.thumperta...o/#entry6879695

 

The older FCR carbs as used on the 426 were also notorious for developing internal leaks between the upper and lower body sections.  If this occurs, you are somewhat out of luck, and the best fix is to grab a used YZ450 carb in good shape and swap it out.



  • Arizo

Posted November 19, 2013 - 07:54 AM

#30

Is there any good methode to see if its an internal leak?

I will try to clean it again.

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  • grayracer513

Posted November 19, 2013 - 09:25 AM

#31

I don't know of one.



  • RoosterJ

Posted November 20, 2013 - 08:33 PM

#32

My problem seem to get worse as time passed, i have had this 426 for several years, always a bear to start. Recently i decided to figure out why so difficult! Acts like stopped up pilot but for grins i checked valves as stated before, timed it all over the place looking at pics of 450 ( thinking i had a 450 ) cam placement i got it close, 450 has two punches, 426 three, i even tryed timing the exhaust to open after intake thus placing cams lobes to each other, what we cannot figure is why the exhaust opens before the intake or near the same time , Most four strokes in diagrams the exhuast comes into play last stroke, i have it on yz timing now no advance on intake or extra retard on exhaust. i have three carbs like this one pilot in one was blocked soild, a 42 came out of bike and was open some, had a 48 and took it a little bigger and it makes real promissing sounds,kicking the kick starter. pulled the carb apart and cleaned the pilot curcuit all the way to throat of carb, closed the start jet and opened larger, every thing in spectrum, seems i had slide plate completely closed so opened to slightly different heights close to factory spec, Its not liking the choke either. checked the coil, changed to another, have not tryed new plug have two and both are firing , wondering about putting the latter model one on with coil in spark plug cap ? anyone know if that will work, maybe a little hotter fire is answer, maybe it needs auto decompression cams that might help, compression is killer, i dont quite understand the trick of setting the manuel release where you let off after loading, will try thou, have a 03 450 with top end off, want to try putting it back together and useing the majic button to start it and see what it says with my carb set up. 426 will start and runs strong if i pull start it, didnt think this would end up being so evasive to cure, maybe i have missed something small ( Could be me ). note :got some c12 thinking poor fuel quality, as high as compression is on these bikes means high octane ? Really wondered about the octane thou ? Would be nice to be able to check this ? maybe the real good stuff might help lighting the fire ( the oxygenated fuel).

  • Arizo

Posted November 21, 2013 - 06:17 AM

#33

i got the mixture screw out, the order it came out was: spring,washer and nothing, no o-ring, it is not in there.

Could this be the problem for hard starting and no idle without choke?



  • grayracer513

Posted November 21, 2013 - 07:45 AM

#34

 what we cannot figure is why the exhaust opens before the intake or near the same time , Most four strokes in diagrams the exhuast comes into play last stroke, i have it on yz timing now no advance on intake or extra retard on exhaust.

 

The exhaust stroke ends the four-stroke cycle, but then what comes next?

 

The next intake stroke, of course, meaning that the intake valve starts to open as the exhaust valve is finishing up closing.  So the exhaust isn't opening before the intake, the whole cycle is just starting over.

 

The YZ426 does not need any more than the 91 octane rating posted on US gas pumps for premium.  The thing with the release lever is easier to understand if you understand the operation of the engine a bit better.  As the piston travels downward on the intake stroke, it fills the cylinder with a fuel/air charge.  Then on the way back up, it compresses the charge, and just before it goes over the top ( TDC ) the plug fires and the power stroke happens.

 

As the piston passes bottom dead center at the end of the intake stroke, the intake valve starts to close, and the piston heads back toward the top.  At about 120 degrees before the piston reaches the top, the valve closes completely, and things come to a halt if you're turning it through with the kick starter.  This is the start of the compression stroke.  From here, the piston has a nearly 4" diameter "stack" of air about 2" high that you have to squeeze down to less than a 1/4" in order to get past TDC.  This is too hard to do, so the rider opens the compression release, which lifts an exhaust valve off its seat.  He can then easily move the kick starter, and he uses that to advance the crank closer to, but not past, TDC.  Now he has a stack of air only an inch high, instead of two inches, to compress in order to kick past the ignition point, and can more easily do so.  What he has done, in effect, is to shorten the compression stroke.

 

Watch:

http://www.yamaha-mo...troke_vid_a.mpg

 

http://www.yamaha-mo...troke_vid_b.mpg



  • grayracer513

Posted November 21, 2013 - 07:47 AM

#35

i got the mixture screw out, the order it came out was: spring,washer and nothing, no o-ring, it is not in there.

Could this be the problem for hard starting and no idle without choke?

 

They very commonly get stuck up inside the bore where the screw lives.  You may need to pull the carb or get a mirror to verify that it's either stuck or actually gone.  But, yes, without the O-ring, you have an air leak, and any number of lean mixture symptoms will occur.



  • Arizo

Posted November 21, 2013 - 08:24 AM

#36

Well i looked again very closely, and the o ring is gone (i think the previous guy din't put it in because the spring and washer where in the wrong order also).

I'm gonna buy an adjustable screw.

 

Other then that, is it normal when i hold my carb upright, that the "M" on the slide is upside down?

i am starting to think i bought this bike from a fool...


Edited by Arizo, November 21, 2013 - 08:26 AM.


  • grayracer513

Posted November 21, 2013 - 08:30 AM

#37

The slide itself can't be assembled upside down.  The vacuum release plate that rides on the engine side of the slide can, however, and to most people, it actually looks like it should.  But the "round" edge goes up, and the "square" edge with the small hole in it goes down.  Be sure the plate isn't cracked or missing a corner, too. 



  • Arizo

Posted November 21, 2013 - 02:59 PM

#38

Ok, well the vacum release plate in the carb at the side of the engine, has a round edge down, the little hole is up, and the M is upside down.

Now i just need to remove the slide and turn the plate i guess? Anything i need to look out for when i do that?

As far as i can see the plate is in good condition.



  • grayracer513

Posted November 21, 2013 - 10:32 PM

#39

The rollers (you'll see them) can drop off the sides of the slide if you aren't careful.  Otherwise, I think you may have found the problem.



  • Arizo

Posted November 25, 2013 - 03:23 AM

#40

Yes i see it, but this screw that i need to remove got messed up. why would the previous owner be so dumb to do this

I am thinking how to remove it, since its in a little axle. Can it take some drilling?

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