Anyone tried the JE Piston for YZ250F

I just bought a high compression (13.5:1) piston because a mechanic friend recommended it and the FMF Powerbomb header. Haven't gotten the pipe yet so was curios as to what you guys think - Is the Powerbomb the best pipe for the 05 YZ250F? Should the muffler be replaced when upgrading the header pipe? From what I've read, the jetting only needs to be tweaked, but I have heard so many different opinions on the higher octane fuel that I don't know what to do there either. Curious to get others opinion here.

I run a JE piston on my big bore, although have never tried just the Hi comp piston. They make good stuff. With 13.5-1 I would run a 50/50 mix of race fuel and 93. You could get by on 93 but I honestly feel like that kind of compression is pushing the limits of 93. Better to be safe.

people keep saying on here that the hi comp reduces the reliability of the motor cause more stress on crank and all that??

because its true, the engine has to do more work to compress more, and in turn makes more power. more power will lower reliablity. plus all the extra compression on the head gaskets, imo, isn't helping them

and hi compression can set off low enough octane fuel before its supposed to and the piston can get a whole into it. thats better safe than sorry

Yea, run good gas 93 will cut it, but personally I wouldn't run it at 13.5:1. I wouldn't really worry about a hole in the piston as much as i would a worn set of crank bearings, rod and wrist pin. 13.5 is very common, but just try to use 50/50 mix to eliminate chances of detonation.

i have about 56+ hours on a JE 13.5 piston right now. i have its replacement (another just like it) waiting for when i get a chance to put it in. at this point it does not *need* it, however.

no one said they break, just said, that with increase power, comes increase stress.

I'm sure the yami can handle it, they put them in stock YZ250F

Thanks for the input, any opinions on the header pipe and muffler?

I might add that we got the piston installed last night and want to tell anyone putting one in to watch the oil ring. It is designed a little differently with a small ridge on the inside diameter so that it has to be installed first and then work the keeper rings around at the same time on either side of the oil ring or it gets bound up in the groove. It was hard for us to see what was going on due to our presbyopia. You young guys don't know what that is but the ones over 40 do! Still need to check valve clearance tonight then button it all back up. I'll post on the valve clearance. It has never been checked. I will also add that I run Rotella 15W oil and the internals looked great!

I will be good to compare, because I just put the 08yzf piston in my 06wr250f. so make sure to keep us posted how it does, your going to love the power, it's longevity that I'm worrie about.

I will be good to compare, because I just put the 08yzf piston in my 06wr250f. so make sure to keep us posted how it does, your going to love the power, it's longevity that I'm worrie about.

If you put the stock one it, its probably going to be more reliable than JE's or Wiseco's. they advertise there stuff as good as stock and sometimes better.

but thats a blunt term(they can mean performanc, not reliablity), i think the stock yz h/c piston comes with three rings. correct?, and these engines are very good engines to begin with.

That piston is gonna wake it up quite a bit, we use JE pistons in our aircooled Vw motors they are great and last.

Got the bike done Wednesday eve and took her for a spin. I didn't get on it too hard yet so I could not tell if it is better or not. It is hard to tell going down a dirt road. The track will be the true test. It seemed to run fine on the pump gas that was still in the tank, but I will probably start mixing it 50/50 with 110 in the future. Intake valve clearance checked well within specs. Exhaust valves were also good but one is approaching the top of the tolerance. I think it will be good until the next time I have to pull the head. The bike is a 2005 model but I have no idea how many hours are on it. I haven't ridden since last summer due to bad get off. Just getting back on the track. Well, I am happy with how the overhaul went and I will just have to ride it hard at the track to know what I need to do next as far as tweaking the jets, etc.

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