250-500cc WR250 squish - slight pinging off idle when starting out

Guys, I recently did the top end on my 99' WR250. I used a Wiseco 2 ring piston, and this time I used the thinner of the 2 gaskets that came in the Athena kit. I heat cycled it a few times then took it on a trail ride. The first ride I took it fairly easy, not holding it wide open or really high RPMs. The second ride I let it rip a bit more. Runs very strong, better than the last time I did a top end. It seemed like my previous jetting was now a little lean for the new top end. I was getting a slight ping just off idle when starting out when hot. I wanted to switch to a PWK 38 for a long time and just did that - 172 main, 45 pilot, I don't have the needle number handy right now. Runs MUCH better with the PWK but still getting this slight ping when hot and seems to be running a little hotter, and sounds weird off idle besides the slight ping.

So I could not find any measurement in the manual or a post on here for measuring the squish. I suspect that since I used the thinner base gasket this might be the culprit. I want to measure this before I go tearing it apart and using a different gasket. Does anyone have the measurement for this?

Even though this is a 99' I suspect the squish would be the same as up to 2014 with the Cagiva engine since the piston is listed as fitting all those years. Any pointers on doing this with the solder method is also appreciated.

is there no procedure like this listed for the later years? this is from my 95 manual. pretty in depth but you know exactly which gasket to use.

as jusintendo states you need to set or confirm your squish
you might need to pull it apart and correct it
you can only do this by topping out the piston in the head to get a proper baseline number, which requires the piston and cylinder removed

Whip the spark plug out and use thin solder bent in an l shape to touch the cylinder wall tgen push kickstarter up to tdc and there should be slight pressure where the solders crushing up, if your squish is tight i dont recommend just smashing in plumbers solder and kicking the thing over it may damage the piston.

My prefered method is tank off drain coolent take head off use modeling clay or plasterscene in four points on the piston blobs of and stick head back on wham that over with kicker and dismantle head use calipers to measure squish.
The manual stated 2.6mm for my bike and thats rubbish as the squish isnt even working at that gap i put mine down to 1.27 mm wich is around 50thou and thats still safe in my opinion, she runs better downlow has bags up top and when i looked at my piston it was scavenging correctly with turbulance marks on the crown.
You can retard the ignition slightly to stop pinking or use higher octane fuel.

Thanks guys! I did finally find this in the manual. I was scouring the sections under engine reassembly. However Italian logic had it under the section of settings and adjustments, like right after adjusting fork compression and rebound! I don't consider this an adjustment, like turning a screw! Go figure. Anyway for the 250 it states 1.4 - 1.5 MM. I'm going to try Juicy's method with the clay. I might take a quick measurement through the sparkplug hole with the solder (very carefully) just as a quick check to see where its at. Swedetech and a few other engine building sites give very detailed instructions about doing it with solder. I have a dial indicator I just don't have the sparkplug hole adapter. The more I think about this I'm about convinced that the thin base gasket is my problem. The first time I rebuilt the motor the factory had 2 base gaskets on it - 2 thin ones to be exact. On that rebuild I used the thicker gasket that came with the kit and had no issues. Thanks for all the input!

Dont bend solder in a L shape and just do one side of the piston the reading will be way way off
Needs to go across the piston in line with the gudgeon pin preferably both sides as in a T shape, If you grab hold of the piston and wiggle it while connected to the rod you will get the jist of how much wobble there is through the whole rod assembly

My 09 wr250 in stock form and new out of the crate, did the same thing. If I went one step richer on the pilot it would quit the detonating but was not as crisp. I checked compression and I had 205psi. I went back to the crisp pilot and started using better fuel and I've had no problems ever since. Although mixing no ethanol 93 50% with Sonoco 110 or VP110 would do the trick I started using 100% vp110 for the fact that it has a 3 year shelf life without the use of additives.

the gaskets are used as shim to compensate for part variation and keep a very close tolerance

Yup your right t shape solder, been so long since ive use it (doh)

Here's a detailed description on how to check squish http://www.rb-designs.com/rb_designs_llc_017.htm. Also, different base gasket thickness will alter your port timing, but I have no idea if it's enough to make a difference.

Update - I checked squish doing the solder test and I have more than enough. Its actually 1.7 where manual calls for 1.4-1.5. That should mean I have lower compression if anything correct? So I believe squish is not the issue.

I also double checked the stator timing mark. I moved the stator plate forward / clockwise about 1/16 of an inch to slightly retard timing. I'm waiting to get a spark plug adapter for my dial indicator so I can measure and make an indicator wire attached to the crank case and a mark on the flywheel at whatever the manual calls for, I think its 5mm BTDC. That way I can check it while idling with a timing light since I don't really trust just going by a mark on the case.

This symptom again is only when the bike is really hot (normal hot operating temperature), after a good ride. Off idle there is a slight clacking type ping and the engine revs a little slower and sounds almost like its lean (same kind of sound as if you were running out of gas). With the PWK I have a 45 pilot which does not seem lean for the low RPM stuff. With that pilot I have to have the air screw 2 turns out so in reality I could probably go to a 42 pilot. Main is a 172. Bike did exactly the same thing with the Mikuni TMX so I really think this is something else. After the low rpm weirdness if I open it up it revs out and pulls hard without an issue. Again this is a new top end with about 2 1/2 hours on it. Piston and ring gap was measured before assembly and all were set to spec.

Plug is gaped correctly (BR8EG). Would the CDI or coil contribute to this issue? Anything else I should check that is affected during the upper operating temperature? I was guessing about CDI or coil since if it was making the timing advanced that might contribute as well. BTW what is the best way to take a measurement of the operating temperature off the radiators when it is acting like this? I have an infrared thermometer but wasn't sure if that would be accurate to point it at the rads.

At this point I'm stumped! Frustrating too as I don't want to ride the bike now in fear of damaging the new top end until this issue is worked out. Any suggestions are appreciated!

look at the rb designs link and get your squish where it should be 1st.I run my squish to the tight side of the tolerance.175 main 42 pilot jd red leanest setting=perfect.bike runs great everywhere

Squish is very important on a 2T. Too much squish is not a good thing and can actually cause detonation.

Still, why would the bike run fantastic for about 20 minutes, then do this. If the squish, compression, and jetting were not right wouldn't it be doing this a bit before that?

perhaps takes a bit to get the heat fully built up, hard to say.

Try a tank of better fuel.

Yea, different fuel is easy enough. The current fuel is 93 octane mixed 40:1 with Bellray H1R. Same gas went into my 2015 300 and ran hood in that

I just thought of something else. I don't think I can use the Husky manual squish measurement for the way I measured the squish. They have you setting the dial indicator with the piston touching the head, then leaving the dial indicator in the head and reassembling the piston on the rod and then measuring how far up it comes. That measurement is taken in the center of the head. By using the solder method through the spark plug hole the outer edges of the piston crown to head should be a different clearance, and I certainly don't have a number to use for that.

I might call Ken O'Connor Racing in CT. He did my crank for me when I rebuilt this motor the first time and may have a recommendation on the squish. The things that are different this time is using the thinner base gasket and a Wiseco vs a Wossner piston.

Also, if the compression is higher overall, I would think another quick test would be trying a higher octane fuel. Either VP or Av Gas. Any thoughts? If that makes it go away, its telling me I'm looking at the thicker base gasket no matter what.

300s have a lot less static compression unless you put on the high compression race head. A good rule of thumb is if your cranking compression is above 185 psi you are probably going to need race fuel. AV gas is about 101 octane and is plenty good for about all 2 strokes. I choose vp110 because it's the cheapest option without having to drive a long distance and buy large quantities to save money.

The more I think about this situation, the fact that the last time I had the .005 gasket and before that the PO or factory had 2 base gaskets under it tells me this particular cylinder and head needed that much space to operate correctly. I don't think I have too little squish per se, but at this level the head probably would need to be reshaped. Everything I read about similar 2 strokes with the same displacement 1.7 on the solder measurement is more than enough, but combustion chamber shape seems to be pretty critical. This old bike (99') I have fun with and have a hard time parting with. I'm not about to go have the head reshaped, or any other measure that would cost a lot of money. I'll probably just break down and pull the cylinder off and put the thicker gasket on. It ran pretty damn good like that last time and the motor will be less stressed as well.

On another note, you guys had me thinking about fuel a lot. I'm near 2 different airports and I checked the prices online last night. 100LL is $4.85. It might make sense to pick some up to enrich the 93 octane 50/50 in all my bikes. I hate the ethanol in the pump gas and it breaks down so quickly.