KX250 big bore

[Pmcg]

Im rebuilding a 1998 kx250 with my brother in law and was tempted to shell out the extra money for Todd's big bore kit.  Im a little nervous that it will be a tuning/reliability nightmare.  Does anyone have 1?  Big power gain?  Do you still run the stock carb and pipe?  Im going to call Todd in the morning and ask him but was interested to hear some personal options. 

Thanks
Pat

[Foxx4Beaver]

I honestly would spend the money on a good port job, and have the power moved to where it would be most useful for the type of riding he's gonna be doing...unless of course he's over 6' and 220+lbs...then opting for a big bore kit would be the better choice, or just find a 500.

I used to send all my 250 cylinders to Pro Circuit, and had them port them for mid-top, and a complete PC exhaust to go with it...I was never disappointed.
Just my opinion.   

[dirk_411]

+1^^

[zz3gmc]

Im building a 04 KX 295 for my wife. No she's not big just likes riding my 500 alot! I have several pipes to try: stock, Enduro Engineering and a Pro Circuit Works pipe. We are going to try the stock carb out first and maybe a APT Smart Carb or Lectron later. It will be set up for enduros and the occasional hare scrambles. Should have the cylinder back at the end of this week.

[hybridkdx]

 One thing people don't think about when going big bore is the loss of port volume. A cylinder that has the ports cleaned up and a small amout of work will be more than impressive

[Pmcg]

I spoke with Todd at Pinsonnault racing today and have decided to go with the 265 big bore kit.  Not going to lose reliability or the power valves and I'll get a bit more low end.  If this is anything like the 500 I'll have a ride report some time next year. 

[zz3gmc]

Not going to lose the powervalves and I dont think reliability will be an issue. If so, I have another cylinder to make it a 250 again. Or Ill swap a 500 into the chassis. Thats what she wanted in the first place! Hoping for a similar but stronger KTM300 like powerband or a nice  grunty , short shifter.

[motopunk]

One thing people don't think about when going big bore is the loss of port volume. A cylinder that has the ports cleaned up and a small amout of work will be more than impressive

agreed... but only tuning for more hp´s does sometimes not effect the wanted plus of torque that a big bore makes with the same hp-delivery .needed for woods, trails etc.
 
as i and my kx-dealer developed the kx360 big bore was the reason to have a bike with the handling of 250 bike and power near to 500cc bikes . 2.reason: to brake the monopole position of the ktm sx360 in the open mx class... 
kawasaki had no interest to produce this engine. but we became green lights to make this kit. major problem was still the headgasket, because of the very less space between the the 78mm bore to the headstuds. we saw that developing a modified bigger cylinder , head and gasket was needed to compare that problem.. but there was the limit. we were not able to go this step... the first real good yamaha and ktm 4strokes came on the plan and to less people asked for big bore 2strokes.
at least it were roundabout 30 engines here in europe. dont know how much still running of them in the new times where all wanted to ride 4 strokes.
i still love to ride this rare engine and enjoy the power delivery.  but the headgasket problem makes me still headscratching time.