help with 02 426, low compression and no start.


72 replies to this topic
  • Florida_426

Posted October 19, 2009 - 08:04 AM

#41

RM,
When the cams are installed and correctly timed you can look at the right side (the cam lobes) and see if the outside lobes of the intake and exhaust are opposed. They should be facing away from each other and look as if you could lay a straight edge on them. If they are not diametrically opposed your gear has slipped on one or the other cams.

Personally I would get a 450 cam from Yamaha or a Hot Cams auot decomp cam and eliminate the drill. I had no problems with the stock set up and could start the bike easily but when I re ringed and shimmed the valves the first time I bought an 03 450 exhaust cam. there are several good threads in the F.A.Q. on timing and doing the 450 DCM job. Keep us posted on what you find.

Bill

  • diegox450

Posted October 19, 2009 - 08:11 AM

#42

Pour some oil inside the cylinder... my WR450 lost almost all compression due to the cylinder getting washed with fuel. Poured a few tea spoons of oil inside and she started inmediately...

Hope you get it ok soon!!

  • 84rm250

Posted October 19, 2009 - 09:06 AM

#43

hey guys thanks for the replys, srry its taking me so long to get back to you.

I clean'd the crab and didnt really find anything dirty. put it all back togethere checking timing after turning it over many times, check'd spark, put oil down the clyinder. primed it with the AP a few times and still nothing.. I kick and kick and dont get anything but a hurt foot and sore leg. i'm going to do a compression test on it today, where abouts should the compression be? Taking to consideration that the rings havent set yet.
Thanks for all the help and replys, keep them coming so togethere we can get this bike running! thanks TT!

  • WA426rider116

Posted October 31, 2009 - 01:09 PM

#44

Well 84rm, I am having similar problems. Mine didn't bend a valve though. I blew a head gasket. Resurfaced the head and Cylinder, still not enough compression to start. Having the cylinder measured now for possibly being out of round. Will let you know what I find.

  • 84rm250

Posted November 01, 2009 - 09:28 PM

#45

Dang, sorry to hear. Yes, please let me know what you find out.

  • wobblyknobby

Posted November 02, 2009 - 12:57 PM

#46

84RM, do you know anyone in your area that has a yz400 or yz426? These bikes are not the easiest to get started, and this could be the problem.

Did you say it fired once and then died? Is the carb slide in good condition? Sometimes they crack. Did you verify the pilot jet was clear? Can you blow thru it and see light thru it? Did you install a new spark plug? Did you verify the compression release is not contacting the lifter cup at TDC?

  • 84rm250

Posted November 02, 2009 - 02:00 PM

#47

Did you say it fired once and then died? Is the carb slide in good condition? Sometimes they crack. Did you verify the pilot jet was clear? Can you blow thru it and see light thru it? Did you install a new spark plug? Did you verify the compression release is not contacting the lifter cup at TDC?


No, Only a buddy with a wr250.
It never fired, just back fired once or twice.
I took carb apart twice and everything look'd good, cleared all the jets.
Replaced spark plug.
Check'd decomp cam and its good, about 1/8 inch before it touches valve bucket.

Any tips on starting it, Besides the video. I'v watched that many times.

  • 84rm250

Posted November 03, 2009 - 10:08 AM

#48

Well I try'd like hell to start it again and got a pop out of it.
took spark plug out to try and do compression check but it turns out i dont have one small enough to fit in spark plug hole. So insted i put a cap part full of oil down the spark plug tube to see if the would help.
Still just end'd up with a sore leg and foot.
Its getting spark.(maybe its to weak?)
Its got enough compression to at least start i would think.
Its getting gas.(maybe i'm flooding it?)
This thing has got me spining on one foot...

  • Sider_steve

Posted November 03, 2009 - 10:50 AM

#49

I had the same problem when I first got my 250 F. I cleaned the carb to try and get it to idle and help with starting. I also ended up with a sore foot. It is a 2001 so it still has manual decompression and isn't the easiest YZ F to start. I was getting frustrated too.
So I decided to try different things. I played with opening the throttle just a bit while I kicked it and that got it to fire. Not sure I would want to try that with a 426 though,they kick back way harder than the 250.Maybe a pull start to get it fired and the carb adjusted.Trying to help save your foot and leg.

  • bakeyz426f

Posted November 03, 2009 - 11:02 AM

#50

can you bump start 426's??????? i think it would work if you put it in gear and got it ready to kick by doing the procedure and then let the clutch out when you have enough speed built up. worth a try mabye IDK

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

Posted November 03, 2009 - 11:07 AM

#51

Will defiantly need good traction and be in a higher gear.
My 250 will bump start out on the trails in second gear if I can keep the back wheel from locking up.I am not sure it will work on a big bore either.

  • wobblyknobby

Posted November 03, 2009 - 04:54 PM

#52

This thing has got me spining on one foot...


:smirk:

84rm,

When you are at TDC:

Your intake(rear) cam lobes should be at exactely 3'clock, pointing directely away from the exhaust cam.

Your exhaust cam lobes should be at around 9:30, pointing slightly up.

There should be exactely 12 pins in the cam chain between the the top "dots" on the cams.
EDIT: Grey is saying 13 pins.

Edited by wobblyknobby, November 04, 2009 - 12:08 AM.


  • wobblyknobby

Posted November 03, 2009 - 05:27 PM

#53

Have you verified the flywheel keys is good, like Grey suggested?

  • grayracer513

Posted November 03, 2009 - 05:35 PM

#54

When you are at TDC:

Your intake(rear) cam lobes should be at exactely 3'clock, pointing directely away from the exhaust cam.

There should be exactely 12 pins in the cam chain between the the top "dots" on the cams.

These two things are not true.

The intake cam should not be at 3:00, but slightly up and rearward. Viewed from the right side, that would be between 9:00 and 10:00. However, the timing marks on the sprockets are what should be used as shown in the manual; the "I" aligned with the head surface on the intake, and the "E" on the exhaust. The visual reference of what the lobe position should look like is useful in determining if the cams have slipped in their sprockets, but not the right way to set timing.

The two marks at or near 12:00 on the cam sprockets are an assembly aid, and should not be used for final judgments as to timing except in extraordinary circumstances. If the cams are set correctly, these two marks will have 13 pins between them.

  • bakeyz426f

Posted November 03, 2009 - 06:08 PM

#55

im timing my wr426f so it has yz426f time and it says i should have 12pins inbetween the marks. is this right?

  • 84rm250

Posted November 04, 2009 - 07:59 AM

#56

Thanks guys, Keyway is good.
With my timing marks lined up I thought I counted 12 pins between the marks. Not really to sure where lobs are but it seems like they are pointing away from each other slighty upwards.

  • grayracer513

Posted November 04, 2009 - 09:46 AM

#57

Should look like this:

Posted Image

Posted Image

  • bakeyz426f

Posted November 04, 2009 - 11:58 AM

#58

those pictures look fimiliar. so i guess my bike had correct timing. im replacing the cam chain and was going to yz time my wr426. i think all i do is rotate the exhaust cam one tooth for yz time. had to stop and cover everthing up cause my yz426f flywheel puller didnt work om my wr426.

  • wobblyknobby

Posted November 04, 2009 - 12:17 PM

#59

I would go with what Grey says and rotate your intake cam clockwise 1 tooth and try that.

Every time I put my 426 back together, I use the "I" & "E" marks on the cams and line them up with the cylinder head surface @ TDC. I never counted the pins between the upper marks. However my Clymer manual does show 12 pins. But for all I know the pic in my YZ400-YZ426 manual could be of a 250f or just be wrong.

Another thing that caught my is that in Greys pic, the intake cam looks like it would line up if it was rotated 1 tooth counterclockwise.

To add to the confusion, some peaple say the YZ timing is 12 pins and the Wr timing is 13. :smirk:

The thing is, the Intake cam has to be indexed correctly to make compression, whether or not the exhaust cam is in WR or YZ phasing so rotate that intake cam clockwise unless it looks way off in that position.

It may be time to take pictures of how your cams are installed.

  • bakeyz426f

Posted November 04, 2009 - 12:29 PM

#60

those pics are from my wr426f. they look a little off in the pic but when i wiggled the rotor a little one way they looked lined up about right to me. the bike ran well as well. i pulled the cam caps and took the nut off the flywheel but im waiting on my puller to come to get off the flywheel. when i time the bike to the yz timing will the exhaust cams marks no loger line up with the head? on this site it says there should be 12pins for the yz timming and 13 for wr timing like mine had above.
http://www.thumperfa...m/yz_timing.htm





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.