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I have a 400 trailblazer and i melted the piston last weekend. Took the top end off of the motor, need a new piston, rings and some machine work.


I bought the bike about 4 months ago, run it around the property and figured it was modded just by the way it ran. I didn't take it apart but it has a KTM exhaust pipe.
The main jet is a 240. As per the manual it is the stock jet. I run the bike at the beack on the sand dunes. What should i really have in it. Some one said i should put a bigger jet in it.

I was thinking of boring it 10 over, but not sure. Not trying to break the bank either.
 

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Do the bore job, then go two steps larger on the main jet for starters. After that do a plug reading to see how it's running. Should be close. The jet is probably why it burned up, running way to lean.
 

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A larger bore by .010", even up to .040" will not require a richer main jet. Been there many times. A lightweight wiseco piston, first size overbore with tolerances for the piston will make a nice difference in how it runs. Just be sure to let it warm up well before every ride. The forged piston expands faster than a cast piston, and many cold seize them because of that. The stock cyl ports are very rough, and a clean and match to the ports on that engine works well. I had porting done by hot seat, and they did a nice job. A friend of mine in Canada does nice port work as well, but any reputable shop could do a clean and match. The intakes should be bead blasted, the exh mirror polished. You need to keep a rough surface on the intakes to keep the fuel mixture atomized properly.
 
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