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mikuni TM34 flatside or stock carb on xr250r

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hey guys, would a TM34 mikuni carb bolt up with no probs to a xr250r? the person thats selling it says it will and its a better carb. IDK..... if so, would it perform better than the stock carb? How so? the stock carb is working fine a lil flat spot,(not too bad, can live with it) so im not really needing to change it out. but if its much better then i'll pick it up. just wondering if its a better carb for my bike thats all. plus its real cheap and in great shape. thanks in advance.

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I had a TM34 carb from XRs Only on a '96 XR280, it was a definite improvement over the stocker. Since the TM34 is not a pumper, the off idle hesitation when quickly snapping open the throttle is still somewhat present, but for me was not an issue.

Edited by creeky

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I have a TM34 for sale, you can try it out to see if you like it.. where do you live?

I had it on my old 280 XR. I did 90MPH on that bike, it screamed. Couldn't figure out the off idle bog though.

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We are using that carb on 250-280-300,but to make it have power.All parts in carb changed,and many other mods to carb.Some bored to 35mm.Also you need change the slide every,few years or the carb body will be worn out.

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you cant just add the 34mm to it without having the XR600R air boot to fit it. think about it. your making that side of the carb that much bigger, the stock air boot wont fit.. maybe if you were really lucky and cut it or streched it. when i got mine it came with the XR600 air boot.

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thanks for the input, im gunna stick with the stocker. off idle hezzy isnt to noticeable. another question, what do a few of ya run for jetting in the stock carb. i run rich says the plug. jets are 135/40. im in the pac. northwest at SL.

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you cant just add the 34mm to it without having the XR600R air boot to fit it. think about it. your making that side of the carb that much bigger, the stock air boot wont fit.. maybe if you were really lucky and cut it or streched it. when i got mine it came with the XR600 air boot.

My TM34 from XRs Only had an aluminum extension adapter on the rear....the 600 air boot sounds like a better answer.

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Just wondering if anyone has any starting point jet suggestions for the TM34 on a stock bore. The carb I'm getting is coming from a higher altitude running 10/190 and I am thinking about getting 35/210 or something to try and start. I've never had a mikuni and I'm clueless about their jet sizing compared to Keihin except the internet appears to rate the jets as smaller per number than Keihin.  I am planning to get an O2 sensor to help with tuning the carb, but I am trading my stock carb and I don't want it to be completely unrideable. 

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I started with 135/195 and the bike seems lean on top and rich at idle with the baffle removed and the XR's only adapter for the stock airbox.

Mid band power is surprising. it doesn't have a bog but it will stumble if you wack the throttle after dropping a gear. Overall very pleased. Starts with no choke so I'm going back to a 130 pilot and maybe a 200-205 main.

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Stick with the stock one.  I am trying to ditch my Mikuni flatslide carburetor on the classified section, I have hours trying to make it work as well as the stock...JC

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If the bike is stock or close to stock then the stock carb with the correct float level ( most stock bikes have too high a float level) works very very well.  With a 280 or better yet the 300 kit then I suggest a Lectron carb in 32mm or a 30 / 32 oval bore. To be honest a 30mm Lectron will have better flow than the stock carb. I think a 34mm is too big in most cases. The flat slide Mikuni is honestly a 2 stroke carb that is adapted to a 4 stroke.

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If the bike is stock or close to stock then the stock carb with the correct float level ( most stock bikes have too high a float level) works very very well.  With a 280 or better yet the 300 kit then I suggest a Lectron carb in 32mm or a 30 / 32 oval bore. To be honest a 30mm Lectron will have better flow than the stock carb. I think a 34mm is too big in most cases. The flat slide Mikuni is honestly a 2 stroke carb that is adapted to a 4 stroke.

All this true big bore,big carb.As Dwight said its two stroke carb.This  is why we change,every part in carb as delivered from Xrs only or sudco.Even that they have jetted them for 4stroke.Not only is there no bog,with big bore and 34mm carb.We have had to detune hit off idle.As it is too strong,for single track riding.

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Baja trail rider

 

Could you detail how you upgrade the TM34 flatside carburetor?  what parts exactly are you changing inside? 

 

also,  as far as the slide wearing out every couple of years, how do you know when its worn?  is it obvious? 

 

finally, I was wondering do you add the extra clutch plate to your xr250 s as well like dwight rudder recommends. 

 

thanks. 

-jay

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Not BTR.. but my 2 cents. 1000MSL. Stock carb with XR's only needle. 190 main. 30 pilot. Needle center. If slide is worn then throttle sticks. bare aluminum doesn't like bare aluminum. Throw carb adapter away. Install XR400 boot on airbox with home made cylinder boot extension. Open up airbox. Free flow slip on. Braaap on.....

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I gotta tell you I hated my TM34, the performance improvement was so slight, it's really not worth mentioning....

 

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I gotta tell you I hated my TM34, the performance improvement was so slight, it's really not worth mentioning....

On My xr300 with the 34 flat slide,big time power. On stock motor not wroth doing. Or if you did not set it up right no improvement.

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