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Old 06-19-2016, 12:13 PM   #1
b44   b44 is offline
 
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Zong 250cc needs more grunt

So ive finally completed rebuild, bike runs sweet, idles fine, starts fine,
Just a few issues
Its got a flat spot around midrange,
I have to get a huge run up to get up moderate incline
Ill start playing with carb settings
Try gearing it down
Weight reduction etc
I wasn't expecting xr250 performance but i also wasn't expecting to be that gutless,
Any help appreciated
Zs169fmm
Keihin pz27 carb
Frame/ unknown


 
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Old 06-20-2016, 08:33 AM   #2
zingshoen   zingshoen is offline
 
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free flowing exhaust, mikuni 26mm round slide carb, 25/115 jets, unifilter...should run nice enough with lower gearing.
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Old 06-20-2016, 12:09 PM   #3
Weldangrind   Weldangrind is offline
 
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Agreed. If you want to play with your existing carb before buying a new Mikuni (which is typically and incorrectly referred to as a 30mm on eBay), try moving the clip on the needle. Make only one change at a time, so you can quantify the result.
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Old 06-20-2016, 12:21 PM   #4
Weldangrind   Weldangrind is offline
 
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In case that's a new language to you, unscrew the cap at the top of the carb and withdraw the slider assembly. You'll see a slot down one side of the slider and that's where the cable is routed. Compress the spring with one hand, and you can pop the cable out.


There will be a clip or disc in the top of the slider that must be popped out, which will reveal the top of the needle. Remove the needle and you'll see the clip that is in one of (likely) five grooves. Note which groove is in use.


I press the open end of the clip down on a hard surface, while holding the closed side with a finger to pop the clip off. That way, it doesn't disappear into another dimension. If you move the clip down one notch, you'll add fuel sooner. if you move the clip up one notch, you'll lean it out a bit. Give it a go, take some pics along the way and tell us what happened.


Please take care to put the slider back in properly; if it is 180 degrees out, the throttle will be wide open. Note that the slider has a small notch on one side at the bottom. That notch (which resembles a small ramp) lines up with the idle speed screw.


Have fun!
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Old 06-20-2016, 11:54 PM   #5
b44   b44 is offline
 
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Good instructions, it was set on the middle of 5 slots i moved it to the bottom one, ; noticed the difference,

Does removing inner baffles & bigger exhaust tip constitute free flowing exhaust?
Its got 48t rear sprocket i think that's why no bottom end pick up, she cruises nicely in top gear
Uni filter is out as carb hardup against frame
Got to remind myself that its only 230cc
Bigger jets next



Last edited by b44; 06-21-2016 at 12:41 AM.
 
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Old 06-22-2016, 01:09 AM   #6
Weldangrind   Weldangrind is offline
 
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Yes, if you remove baffles and increase tube size, it'll be capable of flowing more.
Your gear ratio depends on what size countershaft sprocket you have.
A pod filter could still work, if it has an angled neck. Here's the one I like: http://www.ebay.com/itm/BLACK-42mm-B...FUi8Cu&vxp=mtr
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Old 06-27-2016, 09:19 PM   #7
zingshoen   zingshoen is offline
 
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you can also open up the airbox with a large drill, make 3 holes. not more. for a 3x3 opening mod to run well you ll likely need larger jets and perhaps a differently tapered needle.

as far as gearing goes, if you don t ride roads you can lower it until you have all the response you need. limitation of rear sprocket is the chain guide i guess. my 230 runs really well up to 90 km/h, not a pleasant top speed for long distances, but it gets there quickly.
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Old 07-05-2016, 11:14 AM   #8
b44   b44 is offline
 
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I opened up exhaust by replacing with larger pipe I had lying around, drilled a heap of 10mm holes,stuffed it all back together with rtv,will fit spark arrestor later, angled pod filter on the list.,its putting out more power the more a ride it,piston still wearing in i guess,im actually starting to like it,stoked parts from crf230 fit, i go to my local honda dealer to get odd parts i cant be bothered waiting for ebay,i live close to the beach so paddle rear tyre is the go next, soft sand is a no go
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Old 07-13-2016, 04:24 PM   #9
Ariel Red Hunter   Ariel Red Hunter is offline
 
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Quote:
Originally Posted by b44 View Post
So ive finally completed rebuild, bike runs sweet, idles fine, starts fine,
Just a few issues
Its got a flat spot around midrange,
I have to get a huge run up to get up moderate incline
Ill start playing with carb settings
Try gearing it down
Weight reduction etc
I wasn't expecting xr250 performance but i also wasn't expecting to be that gutless,
Any help appreciated
Zs169fmm
Keihin pz27 carb
Frame/ unknown
Mid range flat spot is a needle adjustment problem. But first, are you sure you have the right main jet in there? I don't mean right according to the factory setting, I mean right according to your engine/exhaust set up. Also it takes about 500 miles to get the new engine parts bedded in. The easy way to check the main jet is to run it for a mile or so wide open. Then choke it a little. If it surges for a second, main jet too lean. If it falls off immedietly - too rich. Main jet performance is from 3/4 throttle to wide open. Needle jet is from 1/4 to 3/4


 
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