2002 YZ426F Problem!! Need help!


10 replies to this topic
  • rufusz

Posted June 29, 2008 - 10:14 PM

#1

Hi guys,

I was riding my bike yesterday around in the city (SM wheels), it ran fine, but on the way home, (i was like in 3rd,4th gear) suddenly the engine started stammering, no power, did pull over, engine runs in idle but the sound in the exhaust is very strange like the gas woul ignite in the exhaust pipe. Or something like that, pretty hard to explain, will try to upload a sound file.
So I've stopped it, looked for cracks/holes, but nothing. Could kick it over, it started on first kick, strange sound still there, try to open the throttle, but it's not gaining rev, just very little, but strange hitting/exploding sound gets louder. If I open the throttle to 1/2, it fires like 15cm flames out of the exhaust.

Pre: Friday I've installed new piston, readjusted valves, cleaned air filter (is still sticky from that blue oil stuff, but that shouldn't be a problem, right?)

Now I'm trying to find out what's the problem. What I know :
- timing is OK (took valve cover off)
- spark could be stronger, but there is spark
- today I will try with a new plug (but I don't think that could cause the problem)
- Don't know about the carburetor !!! Could be some bog there? Not getting enough gas? (tank is almost empty also) Did not mess with the carburetor, did not adjust anything!


So if you have any ideas! Let me know pls! Weather is really nice now and I want to Rideeeeeeeeeeeee! :cry:


:thumbsup: :p

  • 1998YZ400F

Posted June 29, 2008 - 10:52 PM

#2

since you said the timing was good i would give the carb a good cleaning

  • niles

Posted June 30, 2008 - 12:36 AM

#3

Check that a wire isn't grounding out.

  • rufusz

Posted June 30, 2008 - 11:54 PM

#4

which wire should I look for?

  • biznet1

Posted July 01, 2008 - 12:52 AM

#5

Hi guys,

I was riding my bike yesterday around in the city (SM wheels), it ran fine, but on the way home, (i was like in 3rd,4th gear) suddenly the engine started stammering, no power, did pull over, engine runs in idle but the sound in the exhaust is very strange like the gas woul ignite in the exhaust pipe. Or something like that, pretty hard to explain, will try to upload a sound file.
So I've stopped it, looked for cracks/holes, but nothing. Could kick it over, it started on first kick, strange sound still there, try to open the throttle, but it's not gaining rev, just very little, but strange hitting/exploding sound gets louder. If I open the throttle to 1/2, it fires like 15cm flames out of the exhaust.

Pre: Friday I've installed new piston, readjusted valves, cleaned air filter (is still sticky from that blue oil stuff, but that shouldn't be a problem, right?)

Now I'm trying to find out what's the problem. What I know :
- timing is OK (took valve cover off)
- spark could be stronger, but there is spark
- today I will try with a new plug (but I don't think that could cause the problem)
- Don't know about the carburetor !!! Could be some bog there? Not getting enough gas? (tank is almost empty also) Did not mess with the carburetor, did not adjust anything!


So if you have any ideas! Let me know pls! Weather is really nice now and I want to Rideeeeeeeeeeeee! :cry:


:thumbsup: :p


Are you positive about the timing? It seems to me the chain jumped a tooth.

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  • rufusz

Posted July 01, 2008 - 09:37 AM

#6

Hi

Here are the pics :

Posted Image

There is a vertical mark to the right of the "H" mark. Timing was aligned using that mark.

Posted Image

As you can see, exhaust cam is HotCams with marks at 9 and 12 o'clock, right one is stock 426 intake cam, right hand punch mark (at "I") is slightly lower then cylinder head top, left side puch mark (at "E") is higher.


This should be right? Right? :ride:

!!! NEED URGENT ANSWER ON THIS !!!

Problem is I won't be near a computer for the next 24h so if someone could send the answer in an SMS (text message) to +40745373491 that would be sooo great :prof:

PS: I'm curious if I will get a message or a warn :rant: Never seen asking for answer in sms on a forum :cry: lol
I'm desperate...need answer asap...


:thumbsup: :p :cry: :p :worthy:

  • grayracer513

Posted July 01, 2008 - 11:00 AM

#7

The timing is right.

  • rufusz

Posted July 01, 2008 - 12:24 PM

#8

Thx grayracer. :thumbsup:

For what is the "H" mark on the flywheel? If timing should be adjusted according to that "H" mark, then both cams are a few teeth off.

I don't know what else to check on the engine...

Oh I forgot to mention that saturday, after the problem appeared, and I restarted it, the exhaust header got "too soon" red. This could also mean (I think) that ignition is too late, or maybe it ignites only on the wrong TDC. (If I know right, these engine give spark on every cycle when piston is on TDC) :p

Tomorrow I will put it all together and fire it up with a new spark plug and record the sound.

:cry:

  • grayracer513

Posted July 01, 2008 - 01:22 PM

#9

The engine fires on both TDC's, and if it were firing only on the wrong one, it wouldn't run at all.

The "H" mark is for ignition timing.

One thing you could check for is a sheared flywheel key. Do this by removing the spark plug, inserting a Philips screwdriver long enough to reach the piston at TDC, then slowly turn the engine back and forth past the TDC mark while holding the screwdriver to feel where TDC really is. If the mark is way out of agreement with the piston, the key is likely bad.

Your problem sounds like it is in the carb, and that would be the best place t6o look. It could also be a failed CDI, but that is much less likely.

  • rufusz

Posted July 01, 2008 - 10:58 PM

#10

thx grayracer

  • rufusz

Posted July 07, 2008 - 04:00 AM

#11

I finally found out that the CDI box is causing the trouble. Hopefully it's only a connection problem (somewhere), because sometimes it runs good, sometimes not. Replaced it with one from a friend and it run perfect.
I will start with the wires, checking for broken ones, and if nothing, I will take the box apart. Does someone have any info on measuring current / conductivity / resistance / capacity for the wires coming out from the CDI? Any info at all....





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