Posts
664
Joined
1/27/2020
Location
FM
US
Hey guys, finally got my YZ250 (04) back up and running after a full teardown. Never have ridden this bike much as it was a box of parts when I got it. Cut to the chase, I'm getting what I believe to be pre-ignition/spark knock when I really get into it. The inside of the cylinder head cover did have some pitting, so this has happened before.
I'm thinking I'll try some 110 octane mixed 50/50 with 93 just to try that and see if that slows down the combustion enough to see a difference. If so, I may try to adjust the stator plate to retard it a bit.
I've also thought about jetting which I don't see how this could cause pre-ignition, but I read a lot of people lean out the jetting a bit for a pipe and silencer, which this bike does have. I've got a few jets coming above and below the stock size. Do ya'll have any suggestions on that? I called FMF as their site doesn't have any info and they told me to start with the stock jetting and put the clip on the second slot from the top on the needle. Not sure where it is currently, I'll have to take it back apart and see. Don't remember!
Otherwise, this thing runs amazing. Just gotta get this pinging issue solved. Thanks for all advice and suggestions.
I'm thinking I'll try some 110 octane mixed 50/50 with 93 just to try that and see if that slows down the combustion enough to see a difference. If so, I may try to adjust the stator plate to retard it a bit.
I've also thought about jetting which I don't see how this could cause pre-ignition, but I read a lot of people lean out the jetting a bit for a pipe and silencer, which this bike does have. I've got a few jets coming above and below the stock size. Do ya'll have any suggestions on that? I called FMF as their site doesn't have any info and they told me to start with the stock jetting and put the clip on the second slot from the top on the needle. Not sure where it is currently, I'll have to take it back apart and see. Don't remember!
Otherwise, this thing runs amazing. Just gotta get this pinging issue solved. Thanks for all advice and suggestions.
Paw Paw
The Shop
If the knock just starts about 1/2 throttle and goes away toward full throttle, check the power jet. I've seen a clogged power jet and tube cause a knock ( lean spot ) around 1/2 to 3/4 throttle.
As you stated, retarding the timing and jetting to the rich side can also help if you can't find a problem or get better fuel.
Thanks all for the suggestions. I did take a look at the stator plate when I had it apart and someone has effed with it because, like every other damn bolt on the bike, those phillips head screws are pretty screwed up. I thought about adjusting it (retarding) it but wasn't really sure how far to go. My jets should be in today so I'm gonna go for the 180 main and 50 pilot and see what that does. Also, check and see where that clip position is.
Any advice on setting that stator plate? I checked a buddy's YZ and his was right smack in the middle of the adjustment and his has no pinging on 93 octane. I'm not sure which way to go with it, or how far.
Do most people just order VP from their site? I'm not seeing anyone close by me that has it, that's for sure. Have a station about 45 min away that has 110 but went there tuesday and my luck...the pump was broken.
The amount of movement in the stator plate that can throw you off 2 or 3 degrees is amazingly small.
Unfortunately, it's sort of sounding like timing could very well be your problem.
Thanks man.
You can play with jetting, timing and fuels, but until you get the head cut for the proper squish by someone that understands the YZ engine squish issue you will just be putting off what really needs to be done. You may get it where it is acceptable.
Having the head corrected and then rejet and alter fuel octane ratings after that is done will lead you down the correct path to making this issue go away with far less chance of doing damage to your engine.
Paw Paw
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