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So to simplify this, I'm getting an XR100 like next weekend and I was looking for upgrade parts to make it competitive with a crf125, or just make it go faster :smirk:. Ive heard of many of the mods already but i have a very tight budget. Is there any other rejetting or other things I need to do after installing these? I'm thinking FMF header, atc200x carb, bbr120 kit, and modded air filter/ intake. (wanted a hotcam camshaft too but may be out of budget). I really only have about 350 to spend. I was also wondering if the cr80 throttle and cable are really needed for the atc200x catb. And the big question is if i buy these is there anything id have to buy to make them work or fit? nothing worse then brand new parts you cant use...

also is this the 200x carb? http://www.ebay.com/itm/like/301891165034?chn=ps&dispItem=1

 

 

 

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Get a can of octane booster or power booster.
They sell it at Walmart.
You can expect 3dr gear wheelies no problem.
Don't use too much or you can blow the head.
This is  - was a Yamaha 450 we used too much, bad results.

YZFHead2_zps5a1db420[1].jpg

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17 hours ago, jukeltrucc said:

also is this the 200x carb? http://www.ebay.com/itm/like/301891165034?chn=ps&dispItem=1

 

 

 

No, it isn't. But this one is: http://www.ebay.de/itm/ATC-200X-HONDA-1985-ATC-200X-1985-CARBURETOR-/302045849771?hash=item465355e8ab:g:VYAAAOSw65FXtSgO

 

Just notified the carb is incomplete, missing the slide etc. But the body is the right one.

Has to be a Keihin PD62A (or B).

 

P.S.: Octane boosters can cause serious brain damages, ask your local Arthur for more information.

Edited by Alexxxx
  • Haha 1

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On 9/21/2017 at 11:03 AM, Alexxxx said:

No, it isn't. But this one is: http://www.ebay.de/itm/ATC-200X-HONDA-1985-ATC-200X-1985-CARBURETOR-/302045849771?hash=item465355e8ab:g:VYAAAOSw65FXtSgO

 

Just notified the carb is incomplete, missing the slide etc. But the body is the right one.

Has to be a Keihin PD62A (or B).

 

P.S.: Octane boosters can cause serious brain damages, ask your local Arthur for more information.

what other carbs will bolt right on? i heard someone mention a PE24 carb.

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The best carb for a 120 kit is a 200x carb.  Just go to ebay and click used in the filter.  It will have to cleaned.  I use an ultra-sonic tank and soda blasting. Then rejet.  The early CRF150F's uses basically the same carb, if you want new.  

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On 9/20/2017 at 8:49 PM, arthur6 said:

Get a can of octane booster or power booster.
They sell it at Walmart.
You can expect 3dr gear wheelies no problem.
Don't use too much or you can blow the head.
This is  - was a Yamaha 450 we used too much, bad results.

YZFHead2_zps5a1db420[1].jpg

That looks more like RPM related damage than what octane boost could do... valve float would be my first guess or dropped keepers, etc

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The #1 rule on the xr horizontal engine when modding .  Or hell even stock. MUST run a HV oil pump or you will fry the cam journals and all that top end stuff esp with a big bore kit. if your going to tear if half way down might as well get new seals and break it down the cases and do the "squirter mod" if you choose not to buy the oil pump.  Another option vs running a big bore is to run a xr80 cylinder head and use the xr100 camshaft (has more lift over the 80s cam) and or order a high lift cam aftermarket from hotcakes or whatever  >the 80 head flows way better + revs higher and raises the compression a bit with your big bore kit you would likely need a non-domed piston and or double stack the head gaskets this is the go-to " cheater-mod" for alot of road racer and pitbike setup if your using the stock xr100 piston it works without the double gasket and bc the OEM xr100 piston is a flat top so wont have to buy any extra stuff bolt on and go..  another mod is buy an advanced timing key , along with that a  xr80 clutch 1 less disc allows it to rev faster and get the flywheel lightened. I'd almost bet this combo would out run what you listed ;) just saying and is way cheaper. And lastly alot guys also run the xr80 drive sprockets front and rear bc it's a bit lighter less rotating mass. All of this will add power and make the bike prolly twice as quick getting there. 

and note I know the heads can be expensive BUT I scored a 1984 XL80(same as xr80) cylider head off ebay complete for 62$ not all messed up so deals are out there 

Edited by Tx121

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Neat ideas!. I'd just say that rather than double stacking the head gaskets I'd add a spacer under the cylinder instead.. Much less pressure to deal with there. 
I do a lot of work with chainsaws, and the head is part of the cylinder, this is common practice.. 

 

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