YZ250 Pinging Issue

11/17/2020 4:46am
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.
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Paw Paw
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Benton, LA US
11/17/2020 4:53am
The best fix for this is to have the squish corrected by having the head machined. These bikes are built and run right at the raggid edge of self distruction..

Paw Paw
2
FGR01
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Fantasy
1334th
11/17/2020 6:30am
As Paw Paw said, YZ250 stock is jetted right on the edge and pump gas is not really good enough, especially if you are at low elevation or low temps. The manual calls for 95 octane. Real solution is to adjust the head for pump gas as Paw Paw said. If you are going to run the stock head and pump gas, in the meantime you can richen the jetting a little to stop the pinging. Put the N3EW needle in from the newer YZ250's and a 180 or 182 main jet. Start on 2nd clip from top. If it still pings go to 3rd clip from top.
2
11/17/2020 6:33am
Thank y’all for the advice. I am definitely at a low elevation and also getting into lower temps. I’ve read the 95 octane in the manual. I’m getting “labeled” 93 from a crap station close to the house in the woods. I have my doubts about that fuel. I will look into the needle and the jets. I think I got a 180 but not sure I got a 182 to try. Thanks again will take all of these things into consideration!
captmoto
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Rancho Cucamonga, CA US
11/18/2020 9:18am
Motocross action has always recommended running some c12 mixed into pump gas on YZ's. Maybe a 4:1 ratio of pump to race fuel to fight that pinging. A friend of mine runs Bardahl octane booster and MXA again recommends that too. $7 a bottle could be a cheap fix.

The Shop

11/18/2020 9:55am
Being it was a box of parts when you got it you may want to check the ignition timing and squish clearance. Set the jetting as FGR01 suggested with a 50 pilot / 1.5 air screw and you should be okay on 93 octane pump gas at about sea level or above with the correct timing, squish clearance and head volume with no air leaks.

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.
Moto520
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Schaumburg, IL US
11/18/2020 2:40pm
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...
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 have a 2014 YZ250 and i went richer on the main jet by one size. I try to run 50/50 race gas/ pump gas but it's not always available. I have an FMF pipe/ silencer and the V-force. One size richer on the main made the bike run better. It always felt and sounded a little lean before the switch.
11/19/2020 4:07am
I wish I could multi quote.

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. Angry
11/19/2020 7:33am Edited Date/Time 11/20/2020 11:27am
You really have to have a dial indicator that you can put in the spark plug hole and set the piston to the proper height and then align the marks on the flywheel and pick up on the stator. Any other way is pretty much a crap shoot.

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.
11/19/2020 11:05am
Whewwwwweee yeah haha, I'll have to get one of those indicators. Timing has been my thought all along as well but wasn't sure how to get it dialed in specifically.

Thanks man.
Paw Paw
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Location
Benton, LA US
11/19/2020 1:44pm
Just my 2 cents here as many have different opinions..........

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
DynoDan22
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Victorville, CA US
11/19/2020 8:58pm
YZ250's are known to have timing issues and are extremely sensitive to stator placement. As someone mentioned, setting the timing per the service manual is imperative. I've seen them come from the factory advanced a few degrees and they will ping themselves to death. The '99-'04 YZ250 motors were shipped in a high state of tune. There wasn't a huge factor of safety in terms of jetting and ignition timing. If it got a little cold out or the engine was under heavy load, it will ping. Yamaha actually mellowed them out a little by adding some volume to the head and richend the needle in the following years. The world wide spec lowered the compression ratio even more in '10. Those '99-'04 YZ250 motors were really good, you just had to listen for the knock of death.

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