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

locky · Guru

Possible carb replacement ?

Terrence R · Senior Member

I'm not sure why people aren't jumping into this conversation, but I think u just opened my eyes to something really good! I hate the TTR carbs. I can never seem to get the right jets for them and all other parts seem to be on back order at my local Yammy store. You have me wondering now about the NEWER xt250 carbs. I'm ganna do some homework to see if they are also mikuni. If so, I'll be hunting for one. Come to think of it; has anyone tried a WR250f carb conversion?

petenz · Super Guru

I have one of these to go on my TTR...

They are a copy of a OKO.. I put a OKO on my 77 Montesa Cota 348

it now runs like Mr Montesa never thought they could...

http://www.aliexpress.com/item/32mm-34mm-PWK-Carburetor-with-Power-Jet-Black-Color-Universal-Motorcycle-RACING-Carb-Scooters-dirt-bike/32227603941.html

Any 10 jets of your choice for $11.....

http://www.aliexpress.com/item/New-main-jets-for-Keihin-OKO-KOSO-PE-PWK-carburetor-carb-vergaser-choose-your-size-10/1580288731.html

-- Edited by petenz on Friday 6th of February 2015 08:13:18 AM

brindabella · Senior Member

very interesting Pete - will love to hear how it works out eventually on the TTR!

ma77 · Member

I have bought one of those carbs and will add pics when I attempt to fit it. I'm in the uk and at £35 it's 1/10 the price of a new stock carb!

ma77 · Member

Had a go at fitting my oko 34mm today.
Engine side is the same size but filter size is larger. Carb is also a bit shorter but it does physically fit.
Throttle cable does not fit so I have ordered a 1/4 throttle and cable which should work. Hopefully getting jets dialed in won't be too much trouble.

TTRfan · Super Guru

Thanks for the update Matt biggrin

Can you take some pics as you proceed and put them up here for us to see please?

Brian

ma77 · Member

It's on!

Started straight up and ran well. Carb bowl seal needed re positioning but that's it.

I fitted a longer throttle cable as the one I brought was for a pitbike.

Feels faster and more lively but that may be down to the 1/4 throttle.

once warm it would begin hunting at a cruise. Felt lean but plug says rich.

jets are easy to change and don't have to remove float bowl but there are no numbers on the jets.

the carb came with 2 idle and 2 main jets but I have no idea which is bigger or smaller or what's in there :(

ma77 · Member

The only reason for me to do this was to fix my sticky throttle. Which, funnily enough, replacing everything will fix.
Carb to air filter there was a gap which I have used some silicone pipe to fill, will do a neater job soon.
Second starter motor has just said no so may not be jetting as soon as I had hoped :(

Watts · Member

What do you mean when you say, "once warm it would begin hunting at a cruise"?
I too have sticky throttle on the carb.

Baggers · Senior Member

Personally I think the most important thing is how Shiny the new carb is compared to the old one, worth replacing simply for that!!

The Mancunian · Senior Member

Is that link still the same carb?

ttboof · Super Guru

just keep an eye on.the single pull cable set up..the original has the return cable to ensure the slide closes when high vacum is aplied . not as much as an issue for older four strokes and two strokes that the single pull is normaly used on

im keen to see how it goes

petenz · Super Guru

i had a RD400e that started hunting..
after a lot of playing with the carbs it
turned out to be the return spring in
one carb had got weak over time &
the slide was pulseing up/down with the
intake cycle...
i think that was just a one off..but may be
worth looking into..

have to get around to putting the KOSO on
my bike....interested to see how you go...

Bsturkie · Member

Good morning all,

I have recently developed the "sticky slide" syndrome. After my last carb rebuild. After some research, carb cleaner will eat the factory coating away on the slide leaving old slide coating on the walls of the barrel of the carb. Nice! I have though of 2 different plans of attack after finding that pretty much no new OEM slides exist.

First, stronger/additional return spring to bring the slide back despite of the friction. Second, polish the carb barrel with Dremel tool and some sort of buffing compound. Third, attempt to recoat the slide with some sort of clear coat that is resistant to gasoline. Dupont chromabase clear coat? Can the float be turned 180 degrees to introduce different wear surfaces? Something has to be possible. MA77, did you get the replacement carb dialed in?

ma77 · Member

"hunting at a cruise" sat at a steady 30mph the bike would not be smooth - felt like the engine was misfiring.

The single cable setup seams scary as my throttle would stick even with a return cable! I have never had trouble with them in the past and have run out of other options.

Will try sort jetting first as the plug shows the cruise is way too rich.

let us know how you get on fixing your worn slide - the stock carb (working properly) is the best solution

I am waiting for some jets to arrive but its going to be difficult as there are no numbers on the jets so I don't know what I have in the carb at the moment.

Also waiting on all new starter mechanicals as I skimped out the first time round and my new starter and gear only lasted 40 - 50 shut downs

Bsturkie · Member

Quick follow up -

After tearing the carb apart once again, I washed the throat and barrel with 91% isopropyl alcohol and scrubbed with a shop towel. I could tell immediately that any and all residue was being removed. The hard part is getting your fingers all the way in to the slide seat but possible. After that, all looked clean and new. I repeated the process with the slide. No further evidence of coating deterioration. A quick tip I found it to insert the slide in the carb with out connecting the linkage. Move the slide up to its upper most position but low enough to get a finger on the air intake side. Put a bit of pressure on the slide to simulate vacuum and move the slide through it's usual motions. This will help determine where and obstructions maybe. I worked mine over until I could feel hardly any resistance.

Cleaned and lubed the throttle shaft an bushings and reassembled. i also ordered an OEM throttle tube and installed. Cranked and let warm up. I have to say that the throttle action is working better than I have ever seen it. It snaps back with a vengeance now. Took it for a spin around the neighborhood a bit and throttle response is spot on. I will have to say the problem is solved! I cannot say that it won't return in time but we will see. Lesson learned....Carb cleaner is not healthy for some carbs...I'll be cleaning carbs with an alternative from now on. Thanks everyone!

ma77 · Member

I got all the starter stuff replaced and have played with the carb today.

Installed a 40 slow jet but was still misfiring at cruising speed.
Dropped the needle too the lowest setting and is running almost perfectly now.

I'm probably only £60 into a brand new carb. Will have to wait and see how durable it is.

I would probably go for a smaller one if I did this again as throttle response is very sensitive and idle speed screw is almost as low as it goes.

petenz · Super Guru

ma77 wrote:
I got all the starter stuff replaced and have played with the carb today.

Installed a 40 slow jet but was still misfiring at cruising speed.
Dropped the needle too the lowest setting and is running almost perfectly now.

I'm probably only £60 into a brand new carb. Will have to wait and see how durable it is.

I would probably go for a smaller one if I did this again as throttle response is very sensitive and idle speed screw is almost as low as it goes.

Ok.... sounds good... must put mine on sometime , had it almost a year....

40 slow jet / lowest needle setting / Main jet?????

Be a good start point...

the 34mm would prob be a good match for the 325 kit...

.

-- Edited by petenz on Monday 1st of June 2015 06:56:10 AM

leigh · Senior Member

Just spotted this thread. Slides are available via boats.net. I've ordered one and its on its way to me.

It did take 10days for them to get it in from somewhere.

Il be sure to clean the barrel and slide with alcohol and test as suggested. Wonder if I caused the problem with carby cleaner? Hmmm

Cheers Leigh

leigh · Senior Member

Ok installed the new slide. Problem solved.

Much smoother carb operation now. Also cleaned the carb barrel etc and residue the exact same colour as the slide came off the barrel. The new slide was much smoother to touch etc than the old one. Comparing the two quite a bit of coating had come off the old one.

Absolutely nothing else was wrong with the carb, nothing loose, no excess play in anything, all working parts/seals replaced over the last few months (to my limited knowledge). This solved the revving up issue for me. Throttle action is much smoother now, I've always kept the cables and throttle tube well maintained and lubed etc.

Wonder if its just general wear or if carb cleaner compounded the problem? I suspect just wear but my bike has only done 17,000klm.

I can now take the carb out of my bike blindfolded with one hand behind my back :)

Leigh

Minty · Newbie

Hi all,

I have a Koso 34mm carb I tried with a nylon bush on the air intake side to fit straight into the existing air box. Seemed ok, although the carburation wasn't the original problem, so i refitted the original carb. Fitted 140 main jet approx the same as std.

I still have it if anyone struggling with their carb and need an alternative.

PM if interested.