06 YFZ450 starting issue, narrowed down to valve clearance?

[maxamillion]

First off, I tryed posting this at YFZcentral but it wont let me start a topic for some reason...

Okay, my bros YFZ has sat for a few weeks and it isnt starting for us. Here is what Ive tryed so far.

1. The gas should be fine its fairly fresh.
2. Spark plug is 2 months old and it spark when grounded on the frame. We cleaned it so it should be good to go.
3. I cleaned out the carb and blew out the jets with an air hose (it wasnt even dirty tho)
4. battery is fully charged
5. air filter is clean
6. tank petcock is working properly
7. we sprayed starter fluid in carb, still didnt start
8. we tried pull starting it, no luck there either.

So I gave in and called the Yamaha dealer for suggestions. The guy I talked to seemed like he knew his stuff. He said the valve clearance might be to tight causing the motor to make very little compression, therefor not starting. He said it should be adjusted the after the first 20 hours. My bros YFZ prob has around 15-20 hours on it and we have never adjusted the valves (unless he took it to the dealer w/ out me knowing). Should I check the clearance. Is this a common problem? Thanks-Max

[1fst400]

event if thats not the problem its a good thing to do. And you might pick up on the problem while the valves are being adjusted.


I would say a compresion check would be good. but with the auto decomp on the stock exhaust cam I dont think it will work.


does it event sputter? Because if you pull start it event if the valves are out of adjustment, it should start but run like crap


How fast does the motor turn over with the starter. does it sound like its working or like its not building any compresion.

[maxamillion]

Yea I should probably adjust the valves anyways while I got it apart. I just called another local race shop... he said the plug could show spark while grounded on the frame, but that doesnt mean its sparking at the tip of the plug where it needs to.

So Im going to do a compression check like you suggested (so did the race shop). Adjust the valves if compression isnt up to par, I prob will anyways. Then throw in a new plug.

The starter seems to be workin fine its just not firing.

Thanks-Max

[1fst400]

reason I mentioned the starter was that if it spins wicked fast then that could be an indicator of poor compresion.

The decompresion switch on the exhaust cam is designed to allow compresion not to build till the engine is started. So wouldent that meen that your engine would show up with poor compresion on a guage??
I dont know, but that just seems logical to me. Mabie someone eltse can help me out here.

[maxamillion]

Update.....

My bro ended up taking it to the Yami dealer (who actually knows there stuff). The "Gunnar" kill switch he had been using was made to splice in with a certain wire. The dealer said this splicing eventually caused the CDI to short out and it was fried. So they rewired the kill switch to the coil and installed a new stock CDI. They also adjusted the valves (which were a little tight) and adj. the carb.

They charged him $500 but it runs great now.

[2muchquad]

Before you check clearance try a new sparkplug.I know it sounds academic but my yzf used to eat them things.It will spark outside of the cylinder but under the cylinder pressure it wont fire.You can kick until you see stars.;) You'll post back telling me i was right.;)