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XR400 freshen up 426 or ?

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 I'm getting ready to freshen up the top end of my xr400 and I'm trying to decide between this kit http://www.ebay.com/itm/Honda-XR400-XR-400R-88mm-88-426-Big-Bore-Top-End-Rebuild-Kit-Cylinder-Wiseco-/191719616844?fits=Model%3AXR400R&epid=848902216&hash=item2ca361314c:g:ouEAAOSwYGFU1-WQ&vxp=mtr or taking my cylinder in to the machine shop and having it bored to 407 or 415. Either way I will try to stay around 10.1 compression with a Wiseco piston. It would be nice to have the extra power from the 426. I'm also considering a stage 1 Hot cam. My main concern is I do follow my 11 year old son on his xr100 some so I don't want to run into over heating issues in warm south Texas, but I also am starting to do some hare scrambles so it would be nice to have some more power over stock. I already have a Mikuni carb.

Thanks,

Andrew

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i would have thought the gain in the CC increase you suggest would be minimal, the refresh will perk it up.

But then again, when I ride my XR400 off road, it has more power than i think anyone could really want. It'll pull my 100kg bulk up a hill chugging away and still give more when i open the throttle (Edelbrock carb). I can't imagine another 5hp would add to the experience much at all. On the road I get more power might help, but I try to keep off the tarmac to preserve the knobblies.

standard is pretty good

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I went from the stock 398cc straight to 440. The extra power is great. A big bore with the Mikuni you already have is a great combo. Big bore plus hot cam is a little much I think. I was concerned that there's not much you can do to beef up the bottom end and the rest of the engine to reliably handle massive gains long term. I kept the stock cam with no regrets. The extra heat with my 440 is easily managed. I would think a 426 more so.

Don't forget the clutch. If it's time for a top end, then it's also time for a clutch. The extra power and torque of a big bore will expose a worn clutch and weak springs.

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Ditto the clutch.

I did it all, 440cc, HRC Cam, TM40 pumper, XR's only complete exhaust. I race Harescrambles and I follow 5 year olds on 50's. No overheating in Oklahoma.

The power is great, but the XR is by nature happy at low speeds due to low gearing and heavy flywheel.

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4 hours ago, Firestone said:

Ditto the clutch.

I did it all, 440cc, HRC Cam, TM40 pumper, XR's only complete exhaust. I race Harescrambles and I follow 5 year olds on 50's. No overheating in Oklahoma.

The power is great, but the XR is by nature happy at low speeds due to low gearing and heavy flywheel.

Which big bore kit did you go with and what is your compression ratio?

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