I just bought a 85 Honda ATC 200X and starting to rebuild the motor. I was told that it has been bored .40 over already. Do I go .75 over now? How far should I go into the motor? I just have the head off now. I have read swapping the carb out for a xr200 carb.

Any other mods/tips would help(I have searched and read most of the posts pertaining to mods to this bike but would like some more help in choosing the right parts)

thanks!

 

ATC200XXX,

.40 over bore is in inches. This is the same as 1.00 mm. Your cylinder has been bored to 66mm.....which leaves you out of options regarding a piston kit bigger than that except for the Wiseco pistons...which is what you will want to use anyway considering that you are building it for performance. Also keep in mind though, that while there is a piston made larger than the 66mm....the cylinder walls get veeeerrrryyy thin when going larger than this. Many cylinders have become cracked due to the thin wall and the fact that only the high compression pistons are available in those sizes. You are starting with the best available though. The thin wall cylinders last longer when it is the 200X rather than the regular 200 models because the larger fins on the X head keep it running cooler than the regular ones.

Getting back to the matter of piston sizes regarding inches and millimeters here......The best way to keep this in mind so that it is not confusing is........... [ Every .10" oversize in inches equals to .25 millimeters in oversize.] I do not know of any company advertising piston sizes in inches anymore unless it is in addition to the metric sizes. We live in a metric world now....which is a good thing. [img]i/expressions/face-icon-small-happy.gif[/img]

Regarding performance...it's all about how much you want to spend. You can get a moderate boost in power with just the traditional add ons for about $500. This will get you an XR cam, carburetor, intake, 10:1 piston kit, and an exhaust.

Any significant gains above what the above parts will give you requires alot of cash and alot of commitment in keeping your investment for the long term. It's no sense in dumping $2,000 into a 200X engine [which can be done] when you don't know if it's something you plan to keep around for a while. You will never get even half of your money back when you got ready to sell it.

 

Could you give me some part numbers and what years of XRs I need parts from? Thanks!

 

For the carburetor and camshaft, a 2002 XR200R will do fine and be easier for your knuckle head parts guy to locate and order for you.

As for the intake, if you can find one used, the 1980-1984 XR200 is the way to go...however thas has been debate of that working recently.

The only way to go with a new intake is using one from the same model as I listed above [2002 XR200R]. You will have to modify the air intake tube from the carb to the airbox, but that's it.

haywoodjalikme has done this intake and carb mod on his recently and even put pics of the setup on his picture page to better show how it is done. Check that out.

Good luck on your X

 

The piston wall is not scared/grovved so I don't think a bore will be needed but I will check the play.
How does this setup sound? A powroll 66mm bore kit(piston, pin, circlip, gaskets) with the 12:1 high compression. The race cam(.395" lift)with the springs and cam chain.

Will this be too much for the stock bottom end?
Should I just save $ and go with the XR parts?

thanks!

 

Good advice from Knowsalot, listen to him.

I'd stick with the 10:1 piston unless you wanna buy racing fuel which is what you'll need for the 12:1,
its not an issue with me since a buddy of mine has a dirt track racecar and it is easy to get for me.

Oh yeah it $3.50 to $4.00 a gallon, that kinda sucks but the smell of the exhaust is just awesome.

Jeff

 

I'm going with the high comp. setup(unless someone thinks this will not work?) just to use race gas, I like how it smells
I had to get another cylinder off ebay it will have to be bored also. I have a xr200r carb,intake, and a cobra pipe.

I hope the bottom end can take this new power.........

thanks for the help guys

 

I just put an updated and clearer pic of my XR carb set-up on my picture page, it will be up as soon as its approved.

Jeff

 

Cool! I just ordered my intake part # HO16210-kt0-000 from worldofpowersports.com