99/00 yz426f cant get the bugger to start, just bought it to fix


5 replies to this topic
  • Octanee

Posted April 14, 2012 - 06:46 PM

#1

hi guys, so i bought my self for a good price, a 99/00 im told it depends which way you look at it year wise, yz426f, now it wouldnt start, and i figured ok, its gotta be valves, well i takke it apart, sure enough some how the cams where off a bit, so i had it at the I for TDC, and same iwth my 06 yz450f got the dots as best as i could to the flat of the head, however they did not line up perfect, it was either close, or further apart if i knocked 1 back a tooth, so i left it where it sat relatively close but not perfect as it was as perfect as it got.... so i check my valves clearance also, i got about .0012 was it or .012 or so on the 2 exhaust valves and .008 i believe or so, on the intake valves, so im pretty sure its decent there,


so throw it somewhat back together, put gas in tank, and put the choke on, and i got kicking, and kickin, and kickin, some back firing, im holding the decompression valve open, i then took spark plug out, and i have spark, i took it out put some gas in the hole and tried again, pretty much same thing..... just some more back firing then before


but yeah it just wont start, and when you dont have the decompression valve open, you just cant kick the sucker over of course, nor am i trying because i know i could break a gear or something... so it should have more then enough compression

so what gives? ive used a shot of ether twice, before i checked cams, it basically back fired and light airbox on fire lol and not too long ago after it still wont start i gave a very small shot of ether and it lit the airbox on fire for a sec again...

so what gives?! could it be my carbs are in need of a clean?

also some more info on it, guy had it sitting for a year or 2, gas in tank still AND gas line turned on, so carb would of been full for a year or 2 with some baaad gas, so could it really be that?, let me know what ya'll think, i wanna get this going its going to be my spare bike for friends!, Thanks again!

  • over rev

Posted April 14, 2012 - 09:46 PM

#2

I really dont know much about these bikes so take it fwiw.

I was wondering if it was popping out the exhaust, or the intake?

I've been reading about the timing chains, and how these bikes can be hard on them, or sensitive to the chain being stretched. But it seems to me if the chain was stretched, it would be slightly retarded, possibly firing out the exhaust i'm guessing.

either can make for an explosive mixture in the intake as you have seen, It is possible for a proper running machine to backfire while using either.

fresh gas and a clean carb is very important, as i'm sure you know as well. when my pilot was plugged, i could not get my bike to start, i had to spray gas into it. Gas can lose potency in a plastic tank in as little as a few days. as the gas ages, it's octane can be reduced. as the octane is lowered, it becomes more susceptible to pre-ignition.

if this is a type of deal that you just want to hear it fire and run before you sink too much time and money into it, i believe it should do so on gas squirted into the carb. I use a spray bottle with gas in it, i did not have any luck trying to start my new to me 450 on either.

i'm wondering if you could fab up a deal to put compressed air into the cylinder so you could hear if any air was escaping from a poorly seated valve. I have done this by taking the hose off my compression tester, and putting an air line coupler on it. If you have a damaged seat, or valve, i'm guessing you would have the popping.


I'd clean the carb up first, and make sure the pilot, and choke are functioning. it still may need some help to get it started but the carb is a good place to start. if it continues popping no matter what you do, I'd try to see if a valve is not seating properly.

I don't mean to be redundant, or tell you things you already know, I just thought i'd throw in my .02. :thumbsup:

  • Octanee

Posted April 15, 2012 - 09:05 AM

#3

I really dont know much about these bikes so take it fwiw.

I was wondering if it was popping out the exhaust, or the intake?

I've been reading about the timing chains, and how these bikes can be hard on them, or sensitive to the chain being stretched. But it seems to me if the chain was stretched, it would be slightly retarded, possibly firing out the exhaust i'm guessing.

either can make for an explosive mixture in the intake as you have seen, It is possible for a proper running machine to backfire while using either.

fresh gas and a clean carb is very important, as i'm sure you know as well. when my pilot was plugged, i could not get my bike to start, i had to spray gas into it. Gas can lose potency in a plastic tank in as little as a few days. as the gas ages, it's octane can be reduced. as the octane is lowered, it becomes more susceptible to pre-ignition.

if this is a type of deal that you just want to hear it fire and run before you sink too much time and money into it, i believe it should do so on gas squirted into the carb. I use a spray bottle with gas in it, i did not have any luck trying to start my new to me 450 on either.

i'm wondering if you could fab up a deal to put compressed air into the cylinder so you could hear if any air was escaping from a poorly seated valve. I have done this by taking the hose off my compression tester, and putting an air line coupler on it. If you have a damaged seat, or valve, i'm guessing you would have the popping.


I'd clean the carb up first, and make sure the pilot, and choke are functioning. it still may need some help to get it started but the carb is a good place to start. if it continues popping no matter what you do, I'd try to see if a valve is not seating properly.

I don't mean to be redundant, or tell you things you already know, I just thought i'd throw in my .02. :thumbsup:


eh its all good info, i know lots but i guess if people try to help pin point some possible issues, ill be more keen to look into that, but yeah ill pull the carb and clean that sucker out and see what happens

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  • RasmusDK

Posted April 15, 2012 - 05:47 PM

#4

If you hold the decomp lever in you wont get it to start, maybe i read it wrong, but see the FAQ there is a link to a video that shows how to start it. That is THE only way =)

  • grayracer513

Posted April 15, 2012 - 07:21 PM

#5

Watch:

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

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

  • Octanee

Posted April 15, 2012 - 07:37 PM

#6

yep i feel like a idiot, i totally forgot/was not told/reminded that you start a 426 different, its just last time i heard about that fact was like years ago, so it did not come to mind, so any how i seen a vid on youtube after rasmusdk mentioned it on maybe i starting it wrong, and sure enough, i was all like damn bike wont start, i go back out there, turn on gas tank and 2nd kick she fired up, idled strong and throttle great and responsive :thumbsup:

thanks again guys! ha ha i feel dumb right now





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