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Post Info TOPIC: Alternative carbs for the TTR250 - 32mm carb


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32mm carb
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Very jealous of the speed at which your project is travelling! I'm still at the mercy of a foundry with batch processes - got 2 350 barrels cast but probably won't have them heat treated 'till next month 'cause they're about to go into a 2 week summer shutdown. Aaargh. I will probably try a different foundry next time...

Thanks for the cv carb info Chris, by the way. I know the pumper carb works well on my 325 over a wide range of altitude without modifying the jets. If the Koso does too, I will certainly look at it for the 350. I have a mate who's 250 was playing up on a trip we did and he was looking at a cv carb conversion. Decided to give his carb a good clean first, found the pumper jet blocked. Cleaned it and transformed the bike. Who'd have thought it

Wonder if the outside diameters of the in/outlets are larger on the bigger carbs or is it just the throat diameters.

Hope the ribs are healing,
Simon.

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I bought also KOSO carb and jettings. It should come after one month or so. I let you know if I get the same results with the same jettings on my TTR 250 OE.

Today, I a bought a new old bike 1999 DR 350 with electric start. I also planning to try one of bigger cv power jet carbs.
FBRConcepts, could you share with us what device, gauge are you using to get numbers of lean/rich?


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learning to ride on 1993 TTR 250

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bore 28mm - intake 49.5mm / outlet 35mm
bore 30mm - intake 49.5mm / outlet 35mm
bore 32mm - intake 54mm / outlet 40mm
bore 34mm - intake 54mm / outlet 40mm

 

wide band air/fuel ratio gauge & sencer....






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-- Edited by petenz on Monday 24th of July 2017 10:42:34 AM

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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



-- Edited by honda15i on Tuesday 22nd of August 2017 04:43:11 PM

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Today, I lowered needle by one position (clip is raised from center by one level) the hesitation increased from idle to rapid full throttle.

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RE: Alternative carbs for the TTR250 - 32mm carb
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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



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I switched on oem carb.
However it has also problem now - on high rpm it bogs. Main jet or needle needs cleanup/Adjustment

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honda15i wrote:

I switched on oem carb.


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



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I had problems with chinese carb.
It was running great but suddently started
1. Bogging while riding in the middle of ride
2. Started to leak fuel at the end of the ride

I sorted the leaking problem - bowel valve was not closing properly
I could not get rid of bogging problem
Cleaned carb couple times
Changed jets, needle and needle clip position. I was tired with this chinese rubish...

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Ex 1997 and 1998 Honda XR 250



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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 scratchcry

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



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