A forum for owners of Yamaha TTR250 trail and enduro bikes!

Interesting. What brand is the carb ? How does it run with those jets ?

not anything to do with the carb replacement....
a nice pretty set of blue braided brake lines turned
up in my mail box 2 day...




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Had to find more information on this!  How is it running now, looks like this was done a while back from the post date.  did you get the jetting dialed in?  is it still stammering off idle?  maybe due to no accelerator pump?  Its funny because i run a Lectron Carb on my YZ250X and love that thing, zero issues with temp or elevation changes and fires first kick every time cold or hot also improved fuel economy and since installation I have yet to foul a plug (pretty difficult to accomplish that on a 2 stroke without rejetting for various elevations and temp changes).

the Lectron is a Power Jet carb, the adjustment behind slide on top which is for WOT only, wondering if this carb your running is the same?

 

please more information you have a very interested party here!!

 

Thanks!

 

Chris

petenz wrote:

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In my first post I said I put a #50 main jet in,,,, should have been #150..

now running 45 pilot & 152.5 main....
runs great apart from a slight stammer just off idle
if you snap the throttle open...
plug shows its maybe slightly lean at the top...
it starts very easy on a cold motor... thats tells me it
maybe also a tad rich on the pilot jet...

So will go back to the 42 pilot & try a 155 main next..
then fiddle with the needle setting.. see how it goes...
Also it's so easy to change jets... losen the clamps turn the carb
onto a 45* angle un-screw the fuel bowl.... easy easy easy..

how dose it go...
right from when I put it on the first thing I noticed
was the exhaust note was deeper... "GYTR pipe"
It's a lot faster on the throttle & can be a bit
snatchy on & off the throttle "compared to what the TTR
is standard but no worse than a lot of bikes I have
riden/owned..
Power from about mid range seems stronger " seat of the pants dyno"



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Did you ever settle on a good jetting combination that worked over whole rev range?  I have the carb on order and they are going to send me extra jets and needles.  Found a seller local (in the US at least), hoping to have it in hand by Thursday!! Pretty excited, all kinds of fueling issue with the stock carb and just ready to be rid of it for something simpler!!

the stock carb already has everything u need i wouldnt change it its a good carb u can inject it and everything and the acell. pump if its increased u can make the squirt come on faster

and you can bore the stock carb and roughed and polished the intake and exaust and the tourqe curve comes on faster and the us header helps alot for acel and tourqe the short header kills it and the stock pipe de baffled and cut the spark arrester off and stick the stock cap back on and it makes more power than the fmf or yoshi thats just weight diffrence to me

 

I'm wondering if maybe the smallish pilot jet is indicative of the carb bore being smaller than it could be? More vacuum being created due to a higher air speed through the Venturi? I may order a 30mm and a 34mm to play around with.. thoughts?

Chris

OK, so I finally got everything wrapped up on dad's ttr250 and am now in tuning.. I have added a wideband oxygen sensor to the exhaust pipe to help with tuning. initial settings I have the following in the carb:

Pilot: 36
Main:156
Needle center clip
Air Screw was happiest at 1/2 turn out

results were a pretty decent running bike, great throttle response, idled excellent strong mid and top. felt as if it would be great as it was! however.. the wideband was reading some really rich numbers.. below are the wideband results, bike was tested in 6th gear under load but not lugging, it was at a comfortable rpm for the gear, nice and smooth not chuggaluging.

idle AFR- 10.9-11.3
0-1/4 steady in 6th gear was 10.3-10.8
1/4-1/2 steady in 6th gear was 10.8-11.2
1/2-3/4 steady in 6th gear was 11.3-11.7
WOT 11.6-12.0


but the bike felt great everywhere, snappy response, no hesitation off idle, would pull front wheel up in first no problem from a quick blip of the throttle with no clutch and would hold second in the air and gently set it down in the upper rev range. would also lift in second from a roll on but not pick it all the way up but also did not fall instantly either. these are my power/torque comparisons since i have no dyno. and it is related to how the power hits from a low rpm in gear rolling. figured that would be a real world requirement on the trails.

so i decided to see if i could keep the existing power delivery but lean it out so it wasn't so rich. I changed two things at a time:


Pilot: 34
Main:156
Needle raised clip 1 notch (lowered needle)
Air Screw happiest at 2 turns out

Results were as follows:

idle AFR- 14.6-14.9
0-1/4 steady in 6th gear was 12.9-13.3
1/4-1/2 steady in 6th gear was 12.0-12.4
1/2-3/4 steady in 6th gear was 11.7-12.1
WOT 11.6-12.0

ride results, bike definitely lost some of its low end grunt off idle and response was slower, if i blipped the throttle quickly from idle it would hesitate (lean condition). midrange felt slightly weaker and top end felt a little more sluggish as well, lost that strong pull.
being a very good tuner in the automotive community, I would have assumed that this AFR set would be pretty close to good, maybe still a little rich up top, but the bike seems to like to run a bit more on the rich side of things. not sure if it is the single cylinder or because its air cooled maybe?

I am going to switch to a 35 pilot jet next and move the clip back to the center position as i feel that is part of that midrange punch it has lost. i am guessing this will be a very close to perfect setup for this bike down low. after that I will start changing the main jet and playing with the power jet settings!

will report back with my results and findings!

Chris

mine seems to run best with..

38 pilot
155 main
needle on centre groove
think air screw is 1 1/2 turns
not been able to deside where
it really likes to be...

i have the top of the air box cut out & a
short header pipe & GYTR tail pipe/muffler..

going by your figgers I may be to big on the pilot...

I just checked and the needle that came in the 32mm carb is a N68L and the spare is an N68K and appears to be a little longer, i am hoping that resolved my 1/8-3/4 rich condition.. swapping now then will go test and report my findings!

update! the 38 pilot is very close but it looks like a 40 is where it will wind up being perfect.. man the bike feels fantastic, AFR's are dialed in now, I will get some go pro footage once she is perfectly dialed in! the N68K needle is absolutely perfect for this carb and engine setup! glad i decided to try it out! will [post final results after switching to the 40 pilot jet!

Is this info for the 32mm carb on the link above?

Valuable info, what a legend you are. Gives lots of people another carb option, well done sir, well done.

How did you attach it to the bike? Got any pics, I'm guessing you made a spacer like Pete describes?

Cheers Leigh.

Here is the carb, the vent and overflow lines are not routed because i am still accessing the jetting, I will get a picture with everything routed after i button everything up!

 

here is a shot of the spacer on the bike:

 

 

and the spacer on the bench:

 

here is the wideband oxygen sensor setup:

 

 

here is the gauge: 

 

 

-- Edited by FBRConcepts on Friday 14th of July 2017 04:12:03 PM

thats not a silly idea.... A plug & play carb upgrade has it's merits....

that spacer is far better than my hand made one..

yer got another yer want to sell... ?



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FBRConcepts wrote:

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be happy too, but the shipping would be a killer from the USA..

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 Cheaper than you think... I would ship it though NZ post

they have a mailing address in the US.. "Portland"

There calculater says it should cost $16NZ...

(you ship it to them & they ship it to me..)

So what do yer want for one plus postage to portland ?

 

 

 

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When comparing the two needles, the N68K is the longer of the two and that seems to be the one that works best to get the AFR's where they need to be.  If you swap needles, the N68K should be raised 1 notch (move clip lower one notch to be richer from the middle position). this is going to require some additional fuel from the pilot jet since the shorter needle is no longer bleeding into the idle circuit as early from being so short.  I am going to get some footage today of the wideband working through the rev range while riding to show how the combination works!

 

Petenz, sending you a PM!

 

Chris

Found this with a quick google search..  I can attest that a flat slide carb will likely need jetting changes for seasonal or big elevation changes, but its so simple and once you have the base jetting worked out its very simple to change out the pilot, main and adjust needle height if required (pending you use the curved carb cable end on our bikes TTR250's)

 

to directly compare my findings from using the OKO 32mm carb, power and torque is vastly improved and response is there on demand with zero hesitation!  for that kind of performance and as simple as the carbs are, I am sold, no more rubber parts to degrade and require replacement, nothing overly complex, just a simple jetting configuration and you are off to the races!  now that I have figured out what jets and needle and needle setting i can't imagine it would be difficult to copy and be spot on or very close.  I live at sea level on the coast and it is about 92*F here currently.  I will be able to monitor any jetting changes for winter riding and we will make a few trips into the mountains so any other changes for elevation I will record as well.  once done its easy to prepare for a trip to wherever.  I became used to that on my two strokes which are much more picky about air fuel ratios than a 4 stroke.  I would venture a guess that the D slide carb I am using will require little if any changes to perform decently and only require a jetting change if you are after absolute top performance for a race or other situation.

 

here is the write I found below:

 

"Here are the problems with a typical CV carb. Constant Velocity (CV) carburetors are common in many street bike applications because they are able to produce a more smooth acceleration ramp and reduce engine bog, but!!! CV's do prevent an engine from being fed more fuel than it can handle for the given application. 

With a CV carb...the speed at which the slide opens is dependent much more on engine vacuum than physical throttle response or position. Slam the throttle open or try to ramp it on too quickly and the slide only opens as fast as engine vacuum builds. Some of us "Old Timers" that spent hours under a hood with those older style carbs know. Engine modifications can actually hurt performance if vacuum levels are not maintained if staying with a CV carb. 

For example when you are on a trail...just casually cruising along and you "Feel the Need for Speed" or even need a short burst of power to punch over an obstacle or steer through a mud pit, you will have to anticipate what you want from the motor a good amount in advance, not to mention causing over-use of the clutch more than normal. This becomes built-in to muscle memory. If you ever go with a Slide Carb setup you will notice. 

Even removing the stock airbox and going with an aftermarket filter and redneck mod you still are dependant on the design of the CV carb. My opinion they are perfect for Total Stock applications and ease of operation. This is the main reason the design was chosen. 

You can get more performance by going up to a larger diameter CV carb w/accelerator pump + air filter mod's, but you will be nothing close to what the same size carb in a Round Slide or Flat Slide will provide. The Flat Slide yields the best performance, but at the cost of Tuning and investment in time and a jet kit for your elevation and other elevations. The Round Slide is much more forgiving, but you still have to invest in the same Tuning, Jetting and Time, but should be much easier. 

One thing that gets overlooked in certain engine performance mod's is that Intake/Carburetion upgrades-mod's are directly dependant on the quality of the exhaust and vice-versa. I'm definitely not saying that you can't do one without the other, but you will get the best performance gain by doing both at the same time. 

One other item that is not considered when moving to a TM or VM carb is the quality and proper setup of the throttle cable. A normal butterfly is NO WHERE NEAR as sensitive that a slide carb is for proper setup. If your cable is not stiff enough and/or mounted correctly so that there is zero flex you will be chasing jets and needles all over. I found this out first hand and is a basic (hidden) knowledge that I didn't think about until pointed out to me. 

Just like after modification of the clutch and variator parts the logical upgrade is to a Kevlar belt...keeping the stock as a backup belt (my opinion). These performance mods are felt right away and are the best-First steps in the mod process. The exhaust would be the Second step to provide more efficient power and then onto the Third step with an intake and carb upgrade. 

It's up to the buggy owner whether they want to go with the easier-larger CV carb or go with the best option for performance with a Round Slide (VM) carb. The TM carb's are not much more money, but you will spend more time tuning and are on the opposite end of consistency. "

 

OK! carb tuning is complete.. final results are as follows

Pilot Jet 38
Needle N68K clip in middle position with a 1/2 step size shim under the clip is the perfect position (if they make a needle that has the grooves a half step lower it would the perfect jet with clip in middle position!)
Main Jet 150

this gave the best AFR readings and best running engine with the following AFR's

Idle - 14.3-14.8
light cruise -13.7-14.2
light acceleration in higher gears - 13.2-13.6
acceleration from 1/3-2/3 throttle would give a good power enrichment ratio of 12.9-13.4
WOT 12.4-12.9

bike has zero hesitation off idle and revs fast and freely, instant response at all throttle positions, over rev is strong and keeps pulling harder and harder, this did feel flat when richer then 12.0.

bike will wheelie in 1st and 2nd gear with no help from preloading the forks or using the clutch, just roll on the throttle and the front wheel comes right on up no worries! I am truly impressed with this engine now that this carb is on and jetted in! it is a far more impressive setup than the stock setup with stock filter, pipe and carb.  Feels like at least a 5hp increase and big torque improvement as well. 3rd gear will wheelie with clutch no problem.. not sure how else to compare power specs with no dyno nearby but i know from previous experience it would only barely wheelie in first with some form compression help! :)

So I will get some video soon, may be monday, going riding tomorrow and taking the YZ250X as its more sandy and that bike gets on top of the sand a bit faster with 48hp..lol

as it stands I am calling the bike dialed in, I may swap in a 148 main jet to see if it pulls harder under WOT but I find it hard to believe it could be an improvement from how it pulls now!

pulling top gear from a cruise at around 1/3 throttle doesn't require a downshift but under 1/3 throttle seems to want to lug the motor too much at that lower speed for acceleration. it was like this with all jetting changes but is more responsive now with proper air fuel ratios!

what else would anyone like to know about? any pareticular tesats you would like for me to perform?

oh and I am running the stock gearing 13t front 52t rear sprockets, tires are Front 90/90-21 Dunlop AT81F, Rear 110/100-18 Dunlop AT81

Chris

-- Edited by FBRConcepts on Saturday 15th of July 2017 11:17:50 PM

If you have some calipers you could measure and get a close speed for the needles I would think..  I ran across a chat when researching what I had with the carb but can't tell remember where, if I run across it again I'll post up!

 

Chris

Well it will have to wait a bit..I took a nasty spill yesterday and hurt myself a bit, 6 broken ribs (all right side), broken collar bone in two places, and broke my wrist in the process too. No fun... :(


Chris

Any thing worth doing is worth doing well!!  Lol

 

 

Disaster!
Guess that carb's pretty responsive hey?
Take it easy and get well soon,
Simon.

After some bad falls in trials (luckily never broke anything but plenty of pain) I learned that in the choice save me or the bike, it's me! Another rider complicates the issue though. Really bad luck fella. At least you can still type!
Simon.

I can not find OKO 32mm (PWK) carb in web site www.koso.com.tw/products.php.

I only see KSR, KSR EVO and KCR models.

Seems like KSR model DA932300 and DA932301 are 32 mm for 4 stroke. They look very similar.


FBRConcepts and petenz could you guys provide the URI for the exact carb model you bought?


There are plenty of OKO 32 PWK on ebay for 30$-40$. I'm not sure which one to pick.

thanks

this is the one i have from aliexspress...

www.aliexpress.com/item/SUPER-PERFORMANCE-RACING-Carb-Black-PWK-Power-Jet-Carburetor-28mm-30mm-32mm-34mm-Motorcycle-Scooters-dirt/32442944811.html


Main jets
www.aliexpress.com/item/PWK-conversion-speed-glib-KOSO-main-glib-OKO-FCR-long-hexagonal-main-nozzle-main-jet-with/32242092310.html


Pilot jets...
www.aliexpress.com/item/New-12pcs-Set-Slow-Pilot-Jet-for-PWK-Keihin-OKO-CVK-30-31-32-35-38/32817317304.html



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