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Post Info TOPIC: Carb upgrade to a Keihin 36mm PWK


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Carb upgrade to a Keihin 36mm PWK
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My bike has the original Tekei carb bored out, and with a ported and decked head, high comp 2mm OS piston, GYTR muffler and snorkel removed from airbox.   In this configuration it was nice and strong and previously ran 21.5 hp on the dyno. (Up from 17.5hp). Changing just to the Totally TTR's shorty header pipe ( recommended !) ran 23 hp.

I recently upgraded to a 36mm Keihin PWK race carby.  They are cheap enough so nothing ventured, nothing gained.

It bolts in easily enough, just clears the starter motor by mm. (PS Keihin FCR pumpers better carby but 10 times more expensive and bigger and wont fit)

Requires a new throttle cable and throttle assembly (quick pull!)

The PWK is primarily a 2 stroke race carby but will run on 4 strokes.   The jetting was way too fat being set up for 2 strokes.  I think a 150 main.

We had to keep going down on jet sizes 135 130 125 before settling on a 120 main 35 pilot needle clip on 5 so leaned right off.

End result runs so much stronger everywhere down low, mid and especially up top.

It made 25.55 HP at 9350 rpm so a 2.5 hp gain with just a carb swap on this bike. So ten percent for about $100 bux AUD.

It will make power all the way to 10200 rpm where it cuts out ( I didn't know TTR's had a cut out before this!!)

It feels like a more modern water cooled bike in that it now will rev and make power, but retains the TTR,s torqey bottom and mid.

Wheelies so much easier, powerslides on the throttle better.   Will no doubt use more fuel but I built it for performance not economy.

I will now change the 13T front sprocket to a 14T because it pulls so well now

N.B the dyno runs with the new carb were on a different dyno to the previous runs with the original carby.

 I'll post up some pics later when I have more time.



-- Edited by Kaos on Wednesday 2nd of December 2020 12:20:47 AM

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ttr250 dyno.jpgttr250 keihin2.jpgTTR250 keihin 1.jpg



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they are cheap for us in uk £49 & plenty of spares jets float etc

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Yep was $60 AUD delivered was less than $100 including throttle and cable. Had trouble getting a #120 main jet had to solder and drill out a 145.

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Keihin 36.jpg



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Keihin box.jpgNote the fine print on the label race use not highway biggrin



-- Edited by Kaos on Wednesday 2nd of December 2020 11:28:56 AM

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bored Tekei.jpgA pic of the original carby bored out



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That's impressive! Thanks for going into detail on jets as well. Really useful for anyone else trying this mod.

With results like that, do you think the pumper would make much difference, even if it did fit?

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Some great information there Steve!

I had an idea there was a rev limiter built into the CDi but to know that it is set at 10,200rpm is good.

Nice to get affirmation that developing the shorty header was worthwhile! 

Also, I have only heard of the TTR carb being bored but to see one done in the flesh, so to speak, is great! Is it possible to do it with the accelerator jet still in place? I am guessing so.  A little bit more info or a couple more photos from t'other side would be good wink

Your dyno guy sounds really good!



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mossproof wrote:

That's impressive! Thanks for going into detail on jets as well. Really useful for anyone else trying this mod.

With results like that, do you think the pumper would make much difference, even if it did fit?


 I don't know if the Keihin FCR pumper would be better I assume so because it is regarded as the best carb and was used by just about every manufacturer before fuel injection took over.  But the PWK is still a flat slide race carb and a cheap option too.

I just find it interesting that there was a 10 percent gain everywhere in power and torque, and the bigger carb has woken up the top end which was asleep with the original Tekei carb, even though it was bored out.   Where the bike used to flatten off on its power curve and run out of power now it keeps making power with noticeble gains down low as well.

You should try one on the 350!!  The original carb has proven to me to be a restriction on my 263cc motor so I can only assume more of a restriction on the 350 kits.



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TTRfan wrote:

Some great information there Steve!

I had an idea there was a rev limiter built into the CDi but to know that it is set at 10,200rpm is good.

Nice to get affirmation that developing the shorty header was worthwhile! 

Also, I have only heard of the TTR carb being bored but to see one done in the flesh, so to speak, is great! Is it possible to do it with the accelerator jet still in place? I am guessing so.  A little bit more info or a couple more photos from t'other side would be good wink

Your dyno guy sounds really good!


 I'll get some better pics of the old carb and post them up.

The rev limiter suprised me because I've never hit it before and the bike finds it a little to easily nowwink  I'll have to get used to it.

I got lucky with the dyno. It belongs to an engineer /  TT500 enthusiast who build race motors for flat track.  Think alcohol high compression 4 valve converted custom built motors. And my mate who is also building a 4 valve conversion on his TT500 using a TT350 head did all the tuning, I just ride 'em!!

He also tuned my TT350 for Vinduro's, twin 28mm PWK's with ported intake manifold, heads, big bore headers, it hauls ass biggrinbiggrin



-- Edited by Kaos on Thursday 3rd of December 2020 10:32:43 AM

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ttr bike carrier.jpgOff for a dyno tune on the new bike carrier  

ps don't know why its sideways sorry.



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TTR263 dyno.jpg



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To save you burning your eyes out it was 25.55 HP at 9349 RPM and 23 NM at 6961 rpm. Pretty good for 263cc.
The bigger carb gave more power everywhere but enabled the top end to make power too.

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TTr  250 keihin pwk36.jpg



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just clears the starter motor



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Great stuff!
If I'm feeling really enthusiastic in the new year I might try one on the 350. Is there room to spin it round to change jets, or is it still the old carb-off rigmarole?

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Can you post a link to where you got it, I would like to try it on my 350

Well done 👏 very interesting 



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TBH for the price I was expecting a chinese copy it was just an experiment but a genuine Keihin arrived. I just need a 350 kit to bolt on to the Keihin!! My tuner got it in for me.

But for example one of these

https://www.ebay.co.uk/itm/Motorcycle-PWK-36mm-Carburetor-Universal-Motor-Scooter-Dirt-Bike-Carb/274324359393?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D20200520130048%26meid%3D7901ff8fbf2447f680bd3f9697c09380%26pid%3D100005%26rk%3D1%26rkt%3D12%26mehot%3Dpf%26sd%3D323407407948%26itm%3D274324359393%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplAMLv5PairwiseWebWithDarwoV3BBEV2b&_trksid=p2047675.c100005.m1851



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mossproof wrote:

Great stuff!
If I'm feeling really enthusiastic in the new year I might try one on the 350. Is there room to spin it round to change jets, or is it still the old carb-off rigmarole?


 There is just enough room but its so tight its a PITA and found it was quicker and easier to remove it.

And don't forget you'll need a new throttle assembly (quick pull!) and cable, the cable comes in through the top of the carb 2 stroke style.



-- Edited by Kaos on Thursday 10th of December 2020 11:30:50 PM

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Here is a pic of a 38 mm PWK mated to the TTR250 inlet manifold, FYI you 350 owners!pwk38 ttr inlet.jpg



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So this fit right on to the stock intake boot and airbox without any modification ?


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Has anyone fitted the Keihin 36mm PWK to a standard bore ‘uncorked’ motor yet?



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If you do a search for Oko or Koso there are a couple of threads about fitting 32 and 34 mm carbs

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Kaos wrote:
 

I got lucky with the dyno. It belongs to an engineer /  TT500 enthusiast who build race motors for flat track.  Think alcohol high compression 4 valve converted custom built motors. And my mate who is also building a 4 valve conversion on his TT500 using a TT350 head did all the tuning, I just ride 'em!!

 


 ****, I feel lucky if I can borrow a spoke spanner blankstare  biggrin



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