01 yz426 - lotsa questions..


17 replies to this topic
  • nyabinghi

Posted September 10, 2008 - 03:09 AM

#1

ok, so i bought a 01 426 yesterday, and had read up about starting difficulties etc...and have read through the common threads here..

here's the questions...

the seller had difficulty cold starting it - he'd supposedly find tdc, pull the release, advance past tdc and kick it, and when it eventually started it idled and ran nice.. i kicked the bike over slowly a few times cold and noticed that finding tdc was nearly impossible - i never felt it stop me completely, i only got minor resistance... it kicked like a 2 stroke... should i assume somewhere in it's life a auto decomp cam was installed?? - you would think it would be impossible to randomly kick all the way through, without finding tdc unless the cam was changed.....or a valve was screwed up or low compression or something else....as i said bike idled and responded nicely to throttle...

if it does have an auto decomp cam how do you find tdc to kick it? as i said, i can feel the piston moving up and down, but the resistance is minor at tdc - or do you just get a feel for it?

after a minute or 2 of idling header pipe got cherry red, which i've read is semi-normal. i checked intake boot and carb was slightly loose, it may have an airleak issue (it returned to idle fine, until it got real hot, than it gradually creeped up to idle at maybe 3000rpm before i shut it down..i'm assuming tightening carb intake boot up will fix this..and it may make starting easier..)

does the light blue cdi wire mod work?
does the disconnect neutral wire mod work?
does the tps unhook mod work?

i'd rather not tear into the motor/carb if i don't have to...
i plan on picking up some cr8ek plugs today and some engine ice, changing fuel out (seller said fuel was 2 months old..), and re-try starting today.
i know not to touch the throttle while starting etc..

sorry for all the newbie questions! i've had lotsa old 4 strokes, and this one kinda had me thinking..

any other suggestions are appreciated...


thanks!

-greg

  • M0SSLAGER

Posted September 10, 2008 - 03:44 AM

#2

The starting method I use is to pull in the decomp lever and kick it through 3 times, I then release the lever at the bottom of the 3rd kick and let the kick lever return to the top. I then give it a good kick all the way through. If it does not start I then let the kick lever return all the way to the top and crack the decomp lever slightly, push the kick down 2 clicks and then let it return to the top again. I then give it a good kick and it starts. This is my cold starting method with the choke out and seems to work every time.

  • nyabinghi

Posted September 10, 2008 - 04:23 AM

#3

so you're not feeling for tdc at all?

  • M0SSLAGER

Posted September 10, 2008 - 05:26 AM

#4

I don't feel for it I just know where it is through routine.

  • grayracer513

Posted September 10, 2008 - 06:57 AM

#5

.. should i assume somewhere in it's life a auto decomp cam was installed?? -

if it does have an auto decomp cam how do you find tdc to kick it? as i said, i can feel the piston moving up and down, but the resistance is minor at tdc - or do you just get a feel for it?

after a minute or 2 of idling header pipe got cherry red, which i've read is semi-normal. i checked intake boot and carb was slightly loose, it may have an airleak issue (it returned to idle fine, until it got real hot, than it gradually creeped up to idle at maybe 3000rpm before i shut it down..i'm assuming tightening carb intake boot up will fix this..and it may make starting easier..)

does the light blue cdi wire mod work?
does the disconnect neutral wire mod work?
does the tps unhook mod work?

The light blue wire and neutral switch mod are the same thing, but all that they do is fool the CDI into thinking that the bike is in gear all the time. Being in neutral retards the ignition timing slightly to make the bike easier to start. It DOES NOT have any effect on the strength of the spark, but if the bike is not tuned optimally, it might start better with the in-gear timing, which is the result some get with it. IMO, don't bother.

Unhooking the TPS similarly defeats another on board system. The TPS provides throttle load info to the CDI that it uses to generate a "3-D" timing map. Unplugging it puts the CDI in a full throttle mode all the time, so that it can only map timing based on engine speed. This has no effect on full throttle operation, but did work to cover up a fault with the exhaust system in '03-'04 450's. Unless you have a faulty TPS to begin with, this "mod" will do nothing.

The red header is normal, but the idle conditions you describe aren't. It could simply be that the fuel screw needs to be trimmed out, or it could be something more serious.

The normal process for starting a non-modified 426 does not involve finding TDC. You turn the engine up against compression, which should occur in a healthy engine at around 130 degrees before TDC. The release is then pulled, and the piston advanced farther. Back in the day of the big British singles, you moved the engine past TDC, then kicked it through the next stroke. There was enough flywheel mass to carry the engine through the following compression stroke. Not so a YZ426, however, and trying this just gets your foot slammed by the next compression event.

In the YZ426, once compression is found, the starter is advanced only about an inch past that. The piston then is still at a point before TDC on the compression stroke, but you have shortened up the compression stroke to the point where you are only kicking through the last 45-60 degrees of it.

Since auto decompression does basically the same thing by automatically shortening the compression stroke, there's no real need to find anything; you can simply kick it over from any position. It does work a little better to find compression, reset the crank and kick, but it's not strictly necessary.

Your lack of compression could be due to an AD cam installation, in which case, you would not need to use the release at all, and should probably just remove it, or it could be that you have a valve zeroed out. Both these questions can be answered by opening the cam box up and having a look. An AD exhaust cam has a flyweight and spring attached to the sprocket, the original looks just like the intake. Check the valve clearance. If any are at or near zero, you will need to replace the valves.

  • nyabinghi

Posted September 10, 2008 - 12:32 PM

#6

ok, changed plug, switched to hot start knob/no knob (it's 80 degrees here) combo and it started right up (i bet i was flooding it pretty good..). it had a cr6es plug in it... i warmed it up rode it around, let it stall, and used hot start, and it starts right up. i tightened intake boot, and played with idle to get about 1500-1700 and it trucks right along nice.

i spent some time thinking about it before i came back to read the replies.. i realized it wasn't tdc i was looking for.. it's not tdc, it's compression i'm looking for...either way, that helped tremendously..

so i stopped it/started it 4 or 5 times and it started first or second kick hot.. so i got that part figured out i hope.

i know that hard starting cold could mean valve adjustment time.

header pipe is not glowing anymore, and idle is consistent, so i bet the loose carb had just about everything to do with it..

  • 1rkcooper

Posted September 10, 2008 - 07:17 PM

#7

Go to the common threads sticky at the top of the YZ forum and find the Yamaha starting videos at the bottom of the page. If you have auto decompression, and it sounds like you might, the decompression lever does not apply. Everything else in these videos does apply. Keep in mind that every bike seems to have thier own little quirks when starting. Once you learn what your bike needs the only thing left is to enjoy.

  • nyabinghi

Posted September 11, 2008 - 10:44 AM

#8

welp, i couldn't get it to start at all today. a couple of kicks sounded promising. so i just got the ct110 out and rode some lazy trails. too tired to ride hard after kicking the damn thing.

  • matt4x4

Posted September 11, 2008 - 11:17 AM

#9

if you move the kick starter through slow, you should feel compression, pull decomp lever, push kicker 2" further - release both lever and kicker, one good kick Should fire it up - set your right hand on tank - sometimes, when kicking you blip throttle just through body movement although you're CERTAIN you didn't and end up flooding it from the AP circuit.
If your decomp lever is still connected to the head - top front right, then you do not have an auto decom cam.

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  • jbrooks26

Posted September 11, 2008 - 11:36 AM

#10

if you move the kick starter through slow, you should feel compression, pull decomp lever, push kicker 2" further - release both lever and kicker, one good kick Should fire it up - set your right hand on tank - sometimes, when kicking you blip throttle just through body movement although you're CERTAIN you didn't and end up flooding it from the AP circuit.


Pretty good information here. Easy to flood the big four strokes.

If your decomp lever is still connected to the head - top front right, then you do not have an auto decom cam.


Not entirely true. Many people have installed an AD cam and left the decomp lever. The only way to know for sure is to pull the cam cover and take a look at the exhaust cam. Which should be done anyway if you have purchased a used bike. I would have checked the valve clearance right away. Hope this helps.

Josh

  • nyabinghi

Posted September 11, 2008 - 06:36 PM

#11

if i just randomly kick the kicker hard, i'll find the compression stroke everytime. usually about 1/3rd of the way down the kick :thumbsup: and of course it stops me dead in my tracks. after this happens, i pull decomp and push an inch or 2, and kick. sometimes i get a promising burp or 2, but not enough to start.. just enough to fool me into kicking it again....

i try pulling decomp and kicking througha few times to clear the cylinder if i've flooded it. i kick with my hand on the master cylinder. i only twisted the throttle once during the day...

it does almost nothing with the choke on. sometimes it sounds like it'll start with hot start knob on (i'm always assuming it's flooded..). it was 80 degrees here today. with neither knob pulled it doesn't sound like it'll start... i do occasionally get puffs of smoke out of the pipe..

i've tried bump starting it in 3rd and it didn't sound promising..

if i push through slowly, and not hard i can hear intake stroke, and can push right through every bit of the rest. i can lazily push the kicker down 4 or 5 times no problem and not get the major resistance i would assume i should feel...i do get minor resistance from the cams..but nothing like what i'm used to for compression (xl350/xt500 etc..)


i figure either i'm a moron or maybe there's a valve issue. i really don't have time to play with it. i have too many other bikes that start easily, and too many other projects i'd rather play with. i guess it's already lost it's charm. i kinda picked it up hoping for a modern do-all dirt machine. but the frustration of trying to start it has left a sour taste in my mouth...

anybody got anything they want to trade for it?

  • M0SSLAGER

Posted September 11, 2008 - 10:19 PM

#12

When you kick it and it stops you dead in your tracks crack the decomp lever and push about an inch further on the kick lever and then let it return to the top. Then give it a good kick and you should fire up. If it floods turn off the gas and lean it to the left like a bicycle and you will see the gas drain out. Then get on and prime the cylinder with about 8 kicks to clear the plug. I usually start mine with the gas off and turn it on after its running to keep from flooding. Also as others said keep that throttle hand off the grip all together. I keep mine to the left on the bar.

  • Thrasherg

Posted September 12, 2008 - 05:33 AM

#13

No one seems to be reading his posts, you all state to find TDC by feeling for resistance on the kickstart, but he keeps telling you there is no resistance. My YZ stops the kick start dead when the compression stroke starts, it sounds like he has no compression (either auto decompress cam, or some other issue). I think he needs to fit a compression gauge and see if he has any compression. He should also look at the exhaust cam and see if it has the auto-decompress cam. If he has a standard cam and no compression then he has a valve/head-gasket issue, if he has an auto cam, then it might just be a starting technique problem.

Any chance you can look at the exhausts cam? and possibly post a picture or two so we can confirm if it does or doesn't have an auto-decompressor?

  • nyabinghi

Posted September 12, 2008 - 05:34 AM

#14

yeah, i've been thinking it's a valve issue, just haven't had the time to tear into it. i only get dead stop when i randomly wail on it. not when slowly pushing through. which makes me think it's probably a valve not closing/hanging up/sticking/bad valve seat/etc. (i did have bike running for several hours the other day, and it ran fine with no valve noise/problems... no issues aside from really hard cold start. hot start was easy) - i haven't had a chance to put a compression tester on it. i would assume hard cold start is either:
not knowing how to start it.
low compression due to valve or other issue
fuel delivery issue (too much or not enough when cold)
possible air leak on intake side (this has been fixed)
bad plug (new plug was installed yesterday)
bad gas (fresh gas in it)
weak spark (lotsa spark. can't really have weak spark with cdi though - it's either there or not)

so i'm thinking exhaust valve issue. i'll tear into it next week if i have a chance. hopefully a valve or 2 just needs shimmed.

  • grayracer513

Posted September 12, 2008 - 06:21 AM

#15

No one seems to be reading his posts, you all state to find TDC by feeling for resistance on the kickstart, but he keeps telling you there is no resistance.

Did you read mine?

Your lack of compression could be due to an AD cam installation, in which case, you would not need to use the release at all, and should probably just remove it, or it could be that you have a valve zeroed out. Both these questions can be answered by opening the cam box up and having a look. An AD exhaust cam has a flyweight and spring attached to the sprocket, the original looks just like the intake. Check the valve clearance. If any are at or near zero, you will need to replace the valves.

You're right though, most people seem to be missing that point.

  • kevin nichols

Posted September 12, 2008 - 06:27 AM

#16

I had a similiar problem. I checked and adjusted my valves so that they were in spec and it starts right up every time.

  • grayracer513

Posted September 12, 2008 - 06:36 AM

#17

I had a similiar problem. I checked and adjusted my valves so that they were in spec and it starts right up every time.

Now, you need to start paying more frequent attention to your valve clearance to see if it is going to hold at that setting, or continue to close up. If it keeps closing, it's time for new ones.

  • nyabinghi

Posted September 17, 2008 - 11:15 AM

#18

so, i had some free time today, tore the head down, adjusted valves - intakes had closed up a bit... started up easy hot and cold. does not have compression release cam. i must just be a brute..kickstarted too many rotax's i guess!





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