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

Finally, all the parts (carb, jets, throttle grips with cable) arrived.

I manually made twin aluminium gasket 10 mm + 15 mm + two paper gaskets.

The air intake diameter of PWK carb seems to be 4 mm bigger comparing to stock, it fits but take some time to install it into rubber tube.

The fuel/air intake diameter of PWK is 1 mm smaller than standard carb.

I bought throttle grips with cable from https://www.aliexpress.com/item/1-Pair-Rubber-Throttle-Grips-Cable-For-Pit-Dirt-Bike-ATV-With-22mm-Handlebars/32621902548.html?spm=a2g0s.9042311.0.0.kmPSMV

The cable (plastic shield) is to short in the length and the working cable wire is to short too. So, I made my custom cable and it works great.

The carb itself came with two needles and 4 jets from https://www.aliexpress.com/item/SUPER-PERFORMANCE-RACING-Carb-Black-PWK-Power-Jet-Carburetor-28mm-30mm-32mm-34mm-Motorcycle-Scooters-dirt/32442944811.html

My 32mm carb looks the same as petenz owns.

Additional main and pilot jets came from https://www.aliexpress.com/item/New-12pcs-Set-Slow-Pilot-Jet-for-PWK-Keihin-OKO-CVK-30-31-32-35-38/32817317304.html, https://www.aliexpress.com/item/PWK-conversion-speed-glib-KOSO-main-glib-OKO-FCR-long-hexagonal-main-nozzle-main-jet-with/32242092310.html

I installed carb with the same settings as FBRConcepts described:

• pilot jet 38 (this jet came with carb)
• main jet 150.
• The needles do not have any serial numbers. So, I took the longest one and set the clip in the middle (default factory settings).
• The air screw is 1 1/2 turns
• I'm living above 100-150m sea level.

 Bike setup:

• Removed the snorkel rubber from air filter box
• Rear cross tire brand new Pirelli 100/100/18.
• Engine is strong. It produce almost 12Bar compression.
• Exhaust head pipe is stock with removed restriction. Rear muffler is shorten Honda CRF 250R. 
• Gearing is 13/48.
• Fuel 95 octane
• I believe piston is still stock

Carb in action... 

• Bike starts OK cold or hot. I set the idle RPM to 1800. There is a slight stammer just off idle on rapid full throttle movement. If idle rpm is increased til 2500 there is no stammer. The same behavior was with stock carb.
• Without clutch or help from me NO WHEELIES on rapid full throttle on 1st, 2nd gear. If I move my weight to the rear on the seat then on rapid full throttle you can do wheelie on 1 gear. But sitting closer to the tank it is impossible. I need to pull the handle bars to do that. That was same behavior with standard carb.
• With new carb I did test drive 4 hours by riding in the forest and gravel roads, was jumping on the fallen trees. 

Comparisson ...

• I think it performs pretty same like stock carb. Maybe there is 5% increase on power. I'm saying again maybe :)
• This 32mm carb does not have fuel filter inside like the stock has. At the end of riding the rust came into the carb and it started to leak fuel and my trip has ended cause I did not have allen key with me.
• This 32 mm does not have diaphragm, so it should be cheaper to maintain.  

Photos:

https://1drv.ms/f/s!AstbUZulPF2rgwJx1U21mkz3Affp

-- Edited by honda15i on Tuesday 22nd of August 2017 04:33:58 PM

Chris and Arthur have both gone very quiet - is everything OK with your new carbs guys??

Bearing in mind that good s/h original TTR250 carbs are becoming increasingly hard to find, did you think any more about doing an after-market kit with all parts and instructions Steve?

Brian

honda15i wrote:

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I switched on oem carb.

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Can I ask why you gave up on the other carb please? 

We all think that the Chinese stuff will be a good/ cheap alternative and come un-stuck! Don't get me wrong there are some things that are good, but it seems engine components and other critical parts are not up to scratch

Shame really as the cost of the genuine gear is a lot more, but then we never have trouble with it.

I read through the post on using an alternative carb on the TTR 250, so last fall I ordered a 32 mm KOSO carb, an appropriate throttle cable and new twist throttle and pilot and main jets as per suggestions for jetting on this sight.

Now that its installed and I have been running it on back road rides here are my suggestions:

1. its a really cheap carb in the way its made.  the chrome was flaking of the slide new, the jets supplied had no markings on them.......either pilot or main jets, and it came with one needle that is unmarked, on two screws holding the float bowl on.

2.  When i had built my spacer block and went to install the carb I discovered the inlet end of the carb is really no the correct size for the stock Yamaha rubber boot, after fooling with it I was pretty sure it would work ok anyway.  The bell mouth of the carb is too big to fit the stock Yamaha air cleaner snorkle.  I chucked the carb in  my lathe and machined it down to about  2.450 inches, fits snug but doable now.

3. after trail and error jetting and several rides at 60 degree F temps  3200 -4500 ft altitude here in Montana the best jetting I have found is :  148 main jet,   35 pilot,  needle down as far as it will go ( so clip in the top notch on the needle providing leanest running situation ). 67 miles to the gallon on the ride of 127 miles of dirt road and mud and snow section, so good mileage I would judge.  Runs clean, idles, starts with just a little choke rolling it out of warm garage.

4  for a really cheaply mfg carb it runs great..............for how long ?  its simple,  you can change jets easily with the stock tank without removing the carb from the bike.......I loosen carb clamps, tilt carb out, remove slide, then tilt car in and change main jet through the 17mm nut, or remove float bowl to change pilot jet.

5.  it used stock keihin pilot jets, and small round Mikuni main jets, I sorted through 40  or 50  old needles and tried some 4dh4,   4dh2,   dh4-82,  all two stroke needles, all cleaned up the fat spots but where too lean in the mid range and while it ran clean and smooth it had no balls, stock needle taper works best for my bike.

6 no engine mods on my bike,  more air flow in the air box, stock pipe but with a YZ250f  aftermarket quiet insert.  Very quiet bike so the pipe maybe a little restrictive.  UP side I have my bike geared 13/44 for overlanding, and it pulls super good at high gear low throttle .  When I drop main jet or try another needle, the fat strong low throttle pull goes away.

7. carb is fitted with a power jet, and the jet in there  as per has no markings ?  I have not confirmed yet the power jet performs at all or supplies any fuel on top end.

Now that I have ridden the bike on day  long rides, I have lowered my pilot jet size to a 32.  better throttle response in low mid range, cleaner running.

93 miles on mostly slow dirt road with no elevation change,  I used 1.1 gallon of gas.......so   84.5 miles to the gallon, my gps said   19.2 mph average.

oh and this carb definitely adds more power!  would love to try out a shorty header setup with the better breathing carb on, i imagine the combo along with the fmf pipe and airbox mods would net some nice gains!