yz426 starting issue



16 replies to this topic
  • yamahakid426

Posted February 26, 2015 - 03:26 PM

#1

Ive recently done alot of work to my bike, rebuilt the carb, adjusted the timingchain, put in a new airfilter. When i was going to try and start it it was having a hard time running more than likely because of the carb adjustments needing to be made but it started firing so i keep kicking it over, then it started to be able to kick over without the decompression lever being pulled in which isnt right, so i was wondering if anybody knew why this could be happening?. If it is a valve clearence issue or if its just the shear cold holding it up.

  • yamahakid426

Posted February 27, 2015 - 06:14 AM

#2

No it doesnt start now because the its letting all of the compression out i kick it and it doesnt do anything it just hisses a little



  • yamahakid426

Posted February 27, 2015 - 06:40 AM

#3

Yeah it is, i just redid the mechanism before i worked on the bike and it ran fine. It had compression and everything was fine and after i rebuilt the carb and put a new airfilter on and tried starting it it was firing and idleing a little but of course needed tuning and would stall after a couple seconds then randomly when i kicked it again it went through the whole cycle without stopping at tdc and when i kick it over i can hear a hissing from the engine so im not sure if a vavle is bad or it needs shimmed i might just take it to the shop



  • grayracer513

Posted February 27, 2015 - 07:04 AM

#4

Pull the cam cover and check the timing and valve clearance. 



  • yamahakid426

Posted February 27, 2015 - 08:04 AM

#5

I just redid the timing and its on point right now but ill have to check valve clearance



  • Cbogle7

Posted March 02, 2015 - 06:45 AM

#6

I have the same problem it kicks thought and had like a little bit of compression

  • Cbogle7

Posted March 02, 2015 - 06:48 AM

#7

Idk what todo I have replaced rings piston gaskets and set the timeing about ten different times to make sure it's on So I did realize something I have full compression with my cams out of the head but when I put my cams in I loose it all can someone help me I have hhe sed of the titanium valve being wore out but I took my valves out and did a valve job on them but it still doesn't have compression like it should can someone enlighten me please

  • Pooley

Posted March 18, 2015 - 11:34 AM

#8

Idk what todo I have replaced rings piston gaskets and set the timeing about ten different times to make sure it's on So I did realize something I have full compression with my cams out of the head but when I put my cams in I loose it all can someone help me I have hhe sed of the titanium valve being wore out but I took my valves out and did a valve job on them but it still doesn't have compression like it should can someone enlighten me please

Proper punctuation and spelling help us out a ton...

 

Correct me if I have interpreted your post incorrectly.  

 

Without the cams in, you have good compression, meaning that the valves are seating properly and they are sealing fine.  With the cams in, you do not have compression, meaning that they are not seating properly and they are not sealing.  

 

The valve clearances, or timing is not correct.  



Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • grayracer513

Posted March 18, 2015 - 12:55 PM

#9

If you've had the lifters out, check to see if all the shims are completely seated in their pockets.  If one is tilted up, that will cause it.

 

Also, check the veracity of the timing marks.  If the flywheel sheared a key. or wasn't indexed correctly, the ignition will fire at the wrong time, and you'll set the cam timing wrong.  Probe for true Top Dead Center through the spark plug hole with a Phillips screwdriver or the like.  See if the piston is actually at TDC when the marks on the rotor are lined up.

 

Another possibility is that one or the other of your cam sprockets may have slipped, so that while your cams appear to be timed right according to the marks, they aren't, actually.  With the marks lined up correctly, the lobes should look like this:

 

lobes_zpsfs9tdgrj.png



  • Cbogle7

Posted March 19, 2015 - 05:52 AM

#10

I apologize for GRAMMER I was driving lol but anyways what you said is correct about my compression with cams out and cams in and I made sure my shims were all the way down what happens when shims go bad do they expand and get smaller im havey head shimmed today by local shop for under 50 bucks thought it was a great deal and I'll check TDC while I have the head off the bike make sure it's at TDC and that the lines are lined up im really hoping it just my shims because my intake came is tight to turn when it's in the head

  • grayracer513

Posted March 19, 2015 - 06:36 AM

#11

"Grammar", and I still don't see any punctuation.  It's harder to read that way, and as such it's discourteous to those who you expect to read it to deliberately choose not to present it better than that, but apparently you aren't worried about how difficult it is for someone to understand your problem and help you with it as long as you get what you want. 

 

lol

 

Once again, you are going to have to recheck the valve clearance once you torque the head down on the engine, and you may very well find that you need to change one or a couple of them, so IMO, you're wasting your money at the shop. 

 

Shims don't go bad, and they don't have enough mass to expand or contract with heat to a significant degree.  The observation regarding the intake cam is pretty normal sounding.  It isn't unusual for the cam not to spin quite freely in a cold head.  If you are concerned, break out the manual and check the clearance with Plasti-Gage as shown. 



  • Cbogle7

Posted March 19, 2015 - 07:48 AM

#12

Ok thankyou, and the shop has called me and they told me that I need knew intake valves, where can I find the cheapest titanium valves for my bike they are talking 90 a piece for them is there a place to get them cheaper and possibly precut

  • grayracer513

Posted March 19, 2015 - 08:16 AM

#13

Probably not.  And titanium valves are never cut, pre-cut, re-cut, or anything else.  The reason is that titanium cannot be made hard enough to serve as a valve sealing face, and the only reason they can be used for the purpose is that they are coated with an extraordinarily hard material, usually a derivative of titanium nitride (technically a ceramic).  This coating is too hard to be refinished after it's applied, so it has to be applied in an extremely thin layer that's normally only about .0005", or even less.  They can't be touched after they're made, and even lapping them is dangerous to their longevity.  It's the valve seats that are cut or ground to match the valves for proper sealing. 

 

But with a 426, you have the option to use the OEM stainless steel valves from a YZ400 or a 2000 model 426, and those cost a little less than half what the OEM Ti valves do.  You do have to use the correct springs for them (from the same year models) in order to compensate for the fact that they are 40 some percent heavier, but OEM springs are less than $10 each, too.   If I were rebuilding a 426, that's what I would use.



  • Cbogle7

Posted March 19, 2015 - 02:08 PM

#14

Yes I have looked at changing them over and I have seen valves for under ten bucks I just did not think they were legit so didn't give them a chance the only thing is that the spring switch over is expensive but If I can get the spring kit cheap then I'll get my valves off eBay for about ten a piece I would have about 230 in parts

The shop is telling me 360 for three valves and to have them cut and put in and shimmed so I'm just kinda weighing my options out

I would like to go to steel valves about how many more hours will those last over the titanium is my only question

  • grayracer513

Posted March 19, 2015 - 02:34 PM

#15

Maybe 20% longer.  AT current TT OEM parts prices, the Yamaha SS valves with springs are under $200.  That's all 5, including springs.  The shop should be around $20 each to cut the 5 valve seats.



  • Cbogle7

Posted March 20, 2015 - 08:47 AM

#16

Ok they are telling me about 340 for only the three intake valves and three intake springs so where do I get these from that you are finding so cheap

  • grayracer513

Posted March 20, 2015 - 09:21 AM

#17

Any Yamaha parts source.  They are the original equipment for a 2000 YZ426.  The source I used is the TT OEM Parts Store







Related Content

 
x

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.