Jump to content
Sign in to follow this  

Pinging/detonation...still

Recommended Posts

Went for a ride in the sand pits yesterday, bike ran awesome but was pinging pretty hard at WOT, especially under a load (climbing sandy walls). Also, if I ran a gear too tall it would ping pretty bad. I thought I had this sorted out, but hoping you guys can advise me where to go from here. Here's the info:

2006 YZ 250, pc pipe and silencer, boyesen reed, fresh top end. I was riding at 0-600ft and it was 50-55 degrees. 91 octane pump gas mixed 32:1 with Yamalube 2R, 175 main, 48 pilot, JD blue needle on 3rd position, timing set at .006, the plug indicated that the bike was running a tad on the rich side. Should I just retard the timing more?

Share this post


Link to post
Share on other sites

I have two '07 YZ250s. One will drink pump swill and the other will not. Many late model YZs have a squish band in the .07" + range. That's way too much. It causes detonation near the power valve, the hottest area of the piston. Yamaha seems to pull this stunt once in a while. The old open two strokes had the same problem.

The fix is a head mod. Places like http://www.rb-designs.com/ have a fairly inexpensive mod that will both fix the detonation problem and increase, to a certain extent, performance.

Basically you pop the head off and squish some .093 solder between the replaced head and the piston over the wrist pin. You do this about three times and send them with your head. The machinist will them know how much material to remove. He will them machine the combustion chamber to make up for lost volume, or your compression would be way too high. The bonus you get is that Yamaha also made the transition between the combustion chamber and the squish band too round. The head mod fixes that too.

Here's a recent thread that includes some before and after photos. Note the shoulder between the squish band and the head's sealing surface is a lot smaller, the edge between the squish and combustion areas has been made sharper and the combustion are itself has been domed out a bit.

I'll add those photos here.

Before at top.

IMG_6381.jpg

IMG_6380.jpg

Share this post


Link to post
Share on other sites

I think you will need to back the timing off to .004-.002 before you notice any improvement in the detonation.

I run an RB head and it works really well. He turned it around in 4 days.

Share this post


Link to post
Share on other sites

Oh yeah. Timing is what I did to the Blue (detonating) bike as a stop gap for a Utah trip.

You can go to the timing thread and jump through the hoops. Or you can use a hex wrench as a guide and move the stator 2mm counter clockwise. If that doesn't work you can go further. But 2mm is a pretty good first try. You might like what is does to the power too. As a free mod. It is certainly something to play around with. Go some place. Move it around. Test ride it. Monkey with it a lot until you get a feel for some of the things you can do with your timing.

Share this post


Link to post
Share on other sites
How do you know for certain that you have detonation or pinging? IMO, I don't have it. :banana:

I guess I am just assuming that I have detontation by the sound I hear coming from the engine when it's under a load or at WOT :lol: Also, the bike showed signs of detonation when I pulled the old top end apart. Sounds like the RB head mod helps a lot, going riding again this weekend so I will just back the timing off more for now and see what happens.

Share this post


Link to post
Share on other sites

Race Fuel until you get your head fixed

Share this post


Link to post
Share on other sites
How do you know for certain that you have detonation or pinging? IMO, I don't have it. :banana:

It makes a certain sound. Almost like something's rattling around in there.

Share this post


Link to post
Share on other sites
How do you know for certain that you have detonation or pinging? IMO, I don't have it. :banana:

When you hear it, you'll know what it is. It sounds like something loose in the top end, but usually in only one spot of the rpm range....Maybe like a ball-peen hammer hitting the top of the piston.

I agree a head mod is the place to go next. Aftermarket pipes and reeds appear to make the problem worse. If timing and jetting dont do it, you have no other area to turn to. Its a great mod, and well worth doing even if you dont have this issue.

Share this post


Link to post
Share on other sites

I set the timing to .002 last night, I was only able to ride up and down a dirt road a few times so I can't really tell if it helped much yet. Sounds like the head mod is the way to go, changing the timing that much def. made the bike feel a little different though. Thanks for the help guys!

Share this post


Link to post
Share on other sites

Like this...

When you hear it, you'll know what it is. It sounds like something loose in the top end, but usually in only one spot of the rpm range....Maybe like a ball-peen hammer hitting the top of the piston.

I agree a head mod is the place to go next. Aftermarket pipes and reeds appear to make the problem worse. If timing and jetting dont do it, you have no other area to turn to. Its a great mod, and well worth doing even if you dont have this issue.

Share this post


Link to post
Share on other sites

If it is pinging under load at WOT put a bigger main jet in before you melt it.

I don't understand why people are scared to jet the bike up?

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×