Yes, I got it from graphic Mx... Very hard to put on. We did it last night. And this happens.

 

Your needle setting might be goofed. You might have been rich on top and lean in the middle. Just a thought. Your main may be ok but you needle could be messed up. Was it at half throttle or full throttle when you burned down? The needle controls the mid range in the throttle. Might be something to look at. Full throttle burn down is definately a main problem while mid range burn down tends to be the needle setting. Also did you have the crank apart? Are you sure the crank is sealed properly and your crank seals are good? Have seen more burn downs do to air leaks then carb settings. Jay

 

I agree, especially since I run a 260 main in the winter and a 250 main in the summer in my wife's trail mod scrammy. Sounds like a midrange problem

 

I just got an EGT gauge for my 400 (see why on my pic page), I got it from HPD and the chart tops out at 1350 degrees at full throttle. Does anyone know at what temp the piston starts to go?

P.S. I know to check the plug even though I have the gauge. [img]i/expressions/face-icon-small-wink.gif[/img]

 

I moved the clip down one spot. (to the 4th setting) And yes it would cut out about have throttle....And thats where it was at when it blew the hole in the piston. I also was mixing the oil with the gas too. I just don't understand what went wrong...What should I do different if anything? I don't want this to happend again.

 

Hey forgot something it burned the tip of the plug off too.

 

RAJ and I have been talking on the phone , from my experience starting off with a 300 main , and raising the needle (lowering the clip) one position should have had him , if anything , a little to rich .

A #290 main and the clip one slot lower still should make the quad run a little to rich in 50 degree weather , I am trying hard to understand why this quad burned a hole in a piston .

Polaris 400s wil normally stick the rings and roll to a quiet stop when unhappy. RAJ's quad burned a hole , which is from to hot a fire in the combustion area . His jet sizes are close , rich from my experience , I am looking for reasons myself why this happened.

Raj , I'll stick with ya til we get this fixed , and , I'll knock some off the price of the parts to get up and rolling .

Something is dreadfully wrong somewhere to burn holes in pistons with the jets you are using , I'll drop a few nickels to learn whats going on in this situation .

Rick Ritter

 

You stated you were mixing oil and gas also. Is this the normal set up you have on the bike or normally injected. If you are set up to inject and start mixing you better rejet bigger. Oil plus gas going thru jets means less gas. Could be a big problem if not jetted correctly. Or from the sounds of things it could have been an air leak. Did you do an air leak down test when you got it all reassembled?

 

With Rick's Experience and everything I have heard on here about him I would definately look for an air leak. It sounds as if the jetting should have been ok. Check you crank seals. They are famous for ripping out if a crank bearing goes bad. Like Rick said to have a hole burned in the top of the piston something was burning very very hot. You would have been burning very lean to get a hole which apparently is not something that happens often. If you have a massive amount of air leaking in though then you could have a problem like this. Maybe a base gasket was not sealed correctly or the head gasket? Things to check. Jay

 

Just FYI, I holed a piston in my wife's scrammy one time from being too lean in the midrange. Like Rick said, they usually like to seize and stop. One thing for sure, in order to hole a wiseco piston, it definitely got hot on top. With that jetting and clip position, along with being only in Ohio, you should have been ok even with some extra oil in the gas.