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

rodge70 · Veteran Member

RE: carb pipe work

TT-R250M · Super Guru

RE: Carb kit.

TT-R250M · Super Guru

RE: carb pipe work

yamaha42 · Senior Member

Carb jetting help

TT-R250M · Super Guru

There is a few things to check before jumping to conclusions.

Diaphragm Pump

First of all, does your diaphragm pump work?- you can check this by filling the carb bowl with carb removed- check that it squirts a nice stream of fuel from the diaphragm jet. If it does not squirt, unblock the jet or replace the diaphragm.

Okay now...

Pilot Jet

If you have a problem just off idle, it would suggest that something is wrong with the pilot circuit- either blocked circuit or the pilot needs changing.

A Mikuni #42.5 pilot jet would be more suitable as Mikuni sizes are different than Teikei. In theory a #42.5 would be the same as a #52.5 Teikei pilot jet. Same goes with the main jet.

Main Jet

Also, I see from looking at your profile that you have a US model. These bikes run LEAN (from helping other people) so I would suggest a larger main jet. It is hard to say exactly what size you will need but, try a 2-3 size increase. So in theory that would be a Mikuni #129- #130 main jet.

Before you try this though- drop your main jet clip postion to the lowest setting possible (sharp end)- does it still go well after half throttle? If so you would benefit from a larger main jet.

More info on JETTING HERE.

More info on the carb HERE.

Any problems or questions, let me know.

-- Edited by TT-R250M on Tuesday 2nd of April 2013 12:21:34 AM

yamaha42 · Senior Member

TT-R250M wrote:
If you don't mind waiting a few weeks the parts can be bought from HERE. You're in the US so it shouldn't take long.
The standard jets can also be bought from the link above, but if you want to upgrade the jets I am unsure where to buy genuine Teikei jets. If you have trouble, search eBay for a SIGMA JET KIT and you will find THIS.
I have updated the Teikei carb re-build thread, so scroll down to INSTALLING THE NEEDLE SET & you should have no dramas.

I have checked out jet kits on ebay, I am just worried it wouldn't have the correct size jets and would wind up wasting 40 dollars. Also, would i have to change the large jet that the main jet screws into and the needle rides in?

-- Edited by yamaha42 on Tuesday 2nd of April 2013 01:58:35 AM

yamaha42 · Senior Member

1. Yes my diaphragm works

2. My carb is clean. I could try spraying the pilot circut again and blowing it out, but i'm positive it's clean. I was going to use a mikuni vm28/486 52.5 pilot because I don't know where to get Teikei jets and I referred to this thread for the mikuni pilot. http://ttr250.activeboard.com/t49951533/jetting-information/

So you are saying I should use a vm28/486 42.5?

3. Okay, I will pick up a mikuni n102/221 130 jet.

4. By dropping my needle, do you mean dropping the clip so the needle lets more fuel in? (moving the circlip away from the blunt end, towards the pointy end)

5. How do I take my slide out so I can adjust my needle?

TT-R250M · Super Guru

yamaha42 wrote:
1. Yes my diaphragm works
2. My carb is clean. I could try spraying the pilot circut again and blowing it out, but i'm positive it's clean. I was going to use a mikuni vm28/486 52.5 pilot because I don't know where to get Teikei jets and I referred to this thread for the mikuni pilot. http://ttr250.activeboard.com/t49951533/jetting-information/

So you are saying I should use a vm28/486 42.5?
3. Okay, I will pick up a mikuni n102/221 130 jet.
4. By dropping my needle, do you mean dropping the clip so the needle lets more fuel in? (moving the circlip away from the blunt end, towards the pointy end)
5. How do I take my slide out so I can adjust my needle?

In theory Mikuni jets are ten sizes larger than Teikei jets.

That said, a #42.5 pilot jet will be the same as a #52.5 Teikei.

(1.)

By dropping my needle, do you mean dropping the clip so the needle lets more fuel in? (moving the circlip away from the blunt end, towards the pointy end)

Yes, I most certainately do not mean that. If you move the cir-clip to the pointy end you will be able to tell if a bigger main is needed. I wrote it wrong in my last post but I will change it now.

(2.)

How do I take my slide out so I can adjust my needle?

Follow the guide in my Teikei re-build thread.

You do not have to remove the slide arm, only undo the retaining screw like mentioned. Once it is loose & you loosen the two in the slide it comes out with no drama.

.

yamaha42 · Senior Member

Okay I should be able to figure it out. Also, Where can you get Teikei jets and/or teikei rebuild kits?

TT-R250M · Super Guru

If you don't mind waiting a few weeks the parts can be bought from HERE. You're in the US so it shouldn't take long.

The standard jets can also be bought from the link above, but if you want to upgrade the jets I am unsure where to buy genuine Teikei jets. If you have trouble, search eBay for a SIGMA JET KIT and you will find THIS.

I have updated the Teikei carb re-build thread, so scroll down to INSTALLING THE NEEDLE SET & you should have no dramas.

TT-R250M · Super Guru

If you advise the size of jets that you want you should end up with the right size jets. I bought two of these kits. The second kit I wanted a #148 main jet but ended up with another #150 main jet. Maybe #148 would be too small anyway but I still wanted to try it. They are really good quality & have roughly the same size orifice & taper as Genuine YAMAHA. Hope you go well finding the correct size jets.

The part you are talking about is called the nozzle. You will not have to change this, just make sure it is 100% clean. The Mikuni & Sigma jets go straight in if the are the same type of thread pitch (which I'm pretty sure is small round).

I'm not so sure about using Mikuni myself as the orifice & taper in them may not be the same as Genuine & may affect performance. Others have tried & seem to have success so they do work though. Also Mikuni have a slightly different thread pitch so they fit but ''SQUEEK'' in.

yamaha42 · Senior Member

TT-R250M wrote:
If you don't mind waiting a few weeks the parts can be bought from HERE. You're in the US so it shouldn't take long.
The standard jets can also be bought from the link above, but if you want to upgrade the jets I am unsure where to buy genuine Teikei jets. If you have trouble, search eBay for a SIGMA JET KIT and you will find THIS.
I have updated the Teikei carb re-build thread, so scroll down to INSTALLING THE NEEDLE SET & you should have no dramas.
So what comes in that kit? How many main jets, and how many pilot jets?

TT-R250M · Super Guru

yamaha42 wrote:
So what comes in that kit? How many main jets, and how many pilot jets?

It comes with 3 main jets & one pilot. Both times the pilot was #52.5 & I got #145, #140 and #150 main jets (that I will never use).

If you want to pay for shipping I could send you the #145 and #140 main jet if you like?

yamaha42 · Senior Member

TT-R250M wrote:
yamaha42 wrote:
So what comes in that kit? How many main jets, and how many pilot jets?
It comes with 3 main jets & one pilot. Both times the pilot was #52.5 & I got #145, #140 and #150 main jets (that I will never use).
If you want to pay for shipping I could send you the #145 and #140 main jet if you like?

Thanks for the offer, but I think I should just get the whole kit. I have a feeling a different pilot would do the bike good. My bike has an UNI air filter on it, so will the 52.5 pilot work? I'm at 1,800 feet elevation, so should I also swap out the main jet? Should I adjust my needle as well?

TT-R250M · Super Guru

The #52.5 pilot you should have no dramas with.

The main jet will take some trial & error to find the perfect settings. I would suggest to go to #140 main jet & try the jet needle clip position in the middle setting first (standard setting). If it coughs & splutters- try raising the needle (blunt end) until it runs right. If it does not smooth out- go down on main jet size again & revise the method mentioned.

Once the correct main jet & setting is found, try lowering the jet needle by two settings- if it starts to splutter when this has been done, raise the jet needle clip position two settings. This is just to check if it's right. If it's right dropping the needle two settings should make it splutter & backfire (pop) on deceleration.

Any questions or trouble, let me know.

yamaha42 · Senior Member

My bike sputters and backfires now on decelleration. It also runs rough at idle to 1/8 throttle. I'm pretty sure my fuel screw isn't set right, I bent my floats down to compensate for a broken needle and seat. I'm sure the fuel level was lowered...(ordered a new one last week, it should be here any day now) and I will bend the floats back up to the correct position when the new needle and seat get here. Should I removed the seat when replacing the needle? If so, how do you take the seat out?

TT-R250M · Super Guru

Before re-jetting make sure it at least runs properly.

Sounds like you are flooding because the float level is too high or the needle is not shutting off as it should.

I did not have to buy a new needle or seat so I don't see why you will have to unless the seat has been damaged?

Just in case you are not sure how to check the float level, this is how I check, and it seems to work well with all carburetors.

I connect the fuel line to see if it blocks the fuel off at the point shown below in the picture. It is the best way of knowing if this is correct. No fuel should be running or dripping out with the float level with the carb body, as shown below. You can also blow through the inlet with a long piece of pipe attached, but this tends to leave condensation in the inlet, so it's best flushed out with fuel afterwards if this method is used.
Posted Image

yamaha42 · Senior Member

The very tip of my shutoff needle broke, so i ordered a new one.

TT-R250M · Super Guru

yamaha42 wrote:
The very tip of my shutoff needle broke, so i ordered a new one.

When you adjust the float height, make sure tht you remove the float from the chamber. Otherwise you will ruin the valve needle return spring.

Also, DO NOT try to rejet until you have fixed the problem!

yamaha42 · Senior Member

roger that!

yamaha42 · Senior Member

just got my parts, will get to working on it tomorrow

yamaha42 · Senior Member

TT-R250M wrote:
yamaha42 wrote:
The very tip of my shutoff needle broke, so i ordered a new one.
When you adjust the float height, make sure tht you remove the float from the chamber. Otherwise you will ruin the valve needle return spring.
Also, DO NOT try to rejet until you have fixed the problem!

Just fixed my bike, and set the float height back to stock. it's still sputtering so i am going to get a different pilot

TT-R250M · Super Guru

When is it spluttering, at lows revs or high?

Any other symptoms?

yamaha42 · Senior Member

I wouldn't say it sputters, it's choppy if you know what i mean. at idle, it is very rough, i have the idle turned up very high just so it can idle without quitting. even when it's warmed up, when choke is applied the rpm's shoot up to i would say 2,500-3,000? I'm guessing the choke gives the bike the fuel it needs because the pilot is too small. It runs fine after 1/8 throttle, but i'm guessing it's still too lean because of the UNI filter on it. I am going to temporarily put in a Mikuni vm28/486 42.5 pilot and an n102/221 140 main until i get the sigma kit and see how the bike performs.

yamaha42 · Senior Member

RE: Carb issues

TT-R250M · Super Guru

yamaha42 wrote:
fixed with a new needle and seat.

How does she ''rip'' with the new jets? level of satisfaction?

Jarrah

yamaha42 · Senior Member

I haven't ridden my bike in over a month now :(

Mostly neighbor problems... (they say the bike is too loud but we all know how a ttr with stock exhaust sounds right?)

Anyways, I installed a new check valve, bowl gasket, diaphragm, o rings in diphragm pump, and pump cover screws. Also, the tube in the rear tire was leaking. Turned out that it had a nice one-inch slit near the valve stem. Unfortunatly I half-assed the tire mounting and scratched my rim from using flathead screwdrivers.

I just feel like I keep diminishing the value of the bike. First I broke a float valve support in the carb, then I overtightened the airbox bolts, so now the plastic mounting squares are distorted. An airbox mounting bolt broke as well. I then distorted some threads in the diaphragm cover. The screw goes in but It's hard to do so. Now I scratched my rear rim. I think the only thing I did right was bleed my back brake, but while doing so I lost a caliper dirt cover bolt! In addition, I don't have a pressure washer to spray the bike off!

Soon enough I will be riding again, and getting some new hardware to replace my mishaps.

TT-R250M · Super Guru

Sorry to hear that. hmm

Not trying to get on your nerves but I suggest that you buy a light duty torque wrench and put it to test with some specifications from the manual (on something other than your bike). After awhile you will get a feel for the torque needed for different size bolts and it will not be needed unless doing engine work. Don't take this the wrong way, we were all there once.

On a good note, at least you are learning and parts are dirt cheap in the US. wink

Jarrah

yamaha42 · Senior Member

Yes, a torque wrench is a much needed tool that I'm missing from my toolbox.

On a side note, I still haven't mounted my front blinkers. I'm hoping to take a trip to the hardware store sometime to see if they have any hardware I could use to fit them. I'm hoping to be able to drive it this week. It's registered now, so the neighbors can complain all they want but they won't get far ;)

wideload · Veteran Member

Carb

yamaha42 · Senior Member

partzilla.com :)

texasT · Senior Member

Welcome to the fun wideload!

http://ttr250.activeboard.com/t50977624/carb-float-bowl-valve/

http://ttr250.activeboard.com/t49217714/motorcycle-suppliers/

...check out these threads, you might find them helpful blankstare

greg

TTRfan · Super Guru

Carb Cleaning question

TDVT · Senior Member

Going back through my carburetor, gave it a real soak this time & have been more carefully checking all the passages but have a question about one in the intake side (brass fitting to the right of the acel. pump nozzle, see Brain's pic below)

Is this supposed to be clear or is there some sort of stop or plug/ one-way valve?

Thanks!

Andy_C · Veteran Member

Do you mean the brass pin protruding upwards, if you do, then this has no hole or drilling, it should be a blank top.
I recently had my carb. apart and wondered about its purpose too.

TDVT · Senior Member

Did some more searching & it appears those two brass orifices are the air inlets for the pilot jet galley & the main jet galley. I found a site I had bookmarked (& forgotten about) regarding TK carbs as fitted to GpZ's. THIS PAGE has a lot of pics with all the passageways labeled. While cleaning last evening I thought I saw a ball in one but will blame that on the hour & failing eyesight. In blowing the passageways clear with air, you can see/feel air exiting the connected holes but I wasn't able to find where these were connected, hence my post.

There is alot of info on that page (I've posted a link before I think) with cross-sections of TK jets etc. & the author mention the UNsuitablity of Mikuni jets (in his opinion) for the TK.

As for that pin, there IS a small hole on the downstream side which is where fuel from the accelerator pump enters the airflow.

TTRfan · Super Guru

Excellent link Ted. Anyone fancy doing a similar picture show for the exact TTR carb????

Brian

TT-R250M · Super Guru

I have explained this before, these pictures should help...

Any questions- ask

Enjoy!

Jarrah

Andy_C · Veteran Member

Thank you for the correction, I shall look more closely next time I strip it,much appreciated.

TT-R250M · Super Guru

Andy_C wrote:
Do you mean the brass pin protruding upwards, if you do, then this has no hole or drilling, it should be a blank top.
I recently had my carb. apart and wondered about its purpose too.

The accelerator pump nozzle WILL have a hole (not the side shown in picture below) and it must be clean! To test this- remove carb (or airbox) and make sure it is full with fuel. When the throttle is applied it should squirt a nice stream of fuel into the intake. If it does not squirt (common problem), unblock the nozzle with a fine piece of wire. I use compressed air, fuel (or solvent), an old throttle or bike cable after cutting and splitting the strands apart and a pair of pliers to assist with holding the wire and prodding. Check that the one way valve is not blocked (shown below) by filling the carb bowl with fuel and pressing GENTLY down on the diaphragm, it should squirt fuel from the top of the check valve if working correctly (be careful as it could squirt fuel in your eye or shoot the 'one-way check valve' across the room). Also check that your diaphragm is not perished, if it is it will have cracks or it will be hard and brittle. Use Rubber Grease to extend the life of it and all O-rings.

Enjoy!

Jarrah

TT-R250M · Super Guru

Andy_C wrote:
Thank you for the correction, I shall look more closely next time I strip it,much appreciated.

No problems, glad to be of assistance.

Enjoy!

Jarrah

TTRfan · Super Guru

Great pics Jarrah! I think I sometimes blame the pilot jet when maybe I am not checking the airway to it is properly clean disbelief

TT-R250M · Super Guru

TTRfan wrote:
Great pics Jarrah! I think I sometimes blame the pilot jet when maybe I am not checking the airway to it is properly clean

Thanks Brian, the most common cause would be the large air flow O-ring perished (on the side of the carb), but the air jets do get blocked occasionally.

On the subject of the Teikei v's Mikuni main jets- The Teikei main nozzle only has 3mm clearance with Teikei jets (2mm with 6Sigma jets) from the bottom of the fuel chamber. I use the shorter nozzle for my 6Sigma main jet so it has more clearance. I have not measured with the Mikuni jets (as I do not use or intend to use them) but from a fellow forum members findings there is less than 3mm.This is not to mention the flow rates or the tapers of the main jet as these will be different and effect the transition of the jet needle. I guess I could buy a Mikuni jet to check the clearance but it would be a waste of money.

IMO- When upgrading i.e. exhaust, air filter, snorkel- use 6Sigma jets with the shorter, older model main nozzle....unless someone can find a place to buy genuine Teikei jets in larger sizes than standard???

Jarrah

TDVT · Senior Member

TT-R250M wrote:

I guess I could buy a Mikuni jet to check the clearance but it would be a waste of money.
IMO- When upgrading i.e. exhaust, air filter, snorkel- use 6Sigma jets with the shorter, older model main nozzle....unless someone can find a place to buy genuine Teikei jets in larger sizes than standard???
Jarrah
For future reference, I can tell you that a genuine Mikuni round main jet sticks out .160" (4.06mm) beyond the bottom of the emulsion tube. I also just noticed that the main body of the jet does not seat tightly against the end of the tube, not sure of the cause of that.

I like the idea of the shorter main tube & will probably order one to try. The pictures of the jets from the carb re-build thread looked exactly like the Mikuni jets I installed in my TTR last year. It would not surprise me if 6 Sigma are branding/supplying Mikuni style jets for TTRs especially as the #52.5 pilot that you have is a odd Mikuni size (& is also the size specified in the Thumper Talk threads).

On a somewhat side note, I can report that my cleaning was successful & in the end I removed all the bits & pieces I had been mucking with (Mikuni jets included) & have gone bone-stock (US-spec) to get a base-line to try out the various mods one at a time. Should have done that at the outset but.......the bike is running well now.

I can also add that there are fewer & fewer sizes of TK jets available from Yamaha & even though the US manuals specs a #52 pilot it has been superseded to #50 & that is ALL that is available.

TT-R250M · Super Guru

Thanks for the measurement of the Mikuni jets

The 6 Sigma jets are similar to Mikuni jets but do not have Mikuni markings. From your measurements there is a difference in clearance also.

TDVT wrote:
I also just noticed that the main body of the jet does not seat tightly against the end of the tube, not sure of the cause of that.

If you are talking about the main jet not sealing in the thread of the emulsion tube- The Mikuni uses a different thread pitch than Teikei and why the Mikuni ''squeaks'' when installing it.... The 6 Sigma jets do not ''squeak'' when installing and seems to be the same pitch thread(s) as Teikei jets If you are talking about the main nozzle (emulsion tube) not sealing on the main body- this is what the O-ring is for....

If you are talking about the Mikuni main jet not sealing at the tip of the nozzle- I can only suggest that the Mikuni main jet is not round enough to seal (I know the 6 Sigma jets seal, as do the Teikei jets).

Glad you got it sorted.

Jarrah

TT-R250M · Super Guru

TDVT wrote:

The pictures of the jets from the carb re-build thread looked exactly like the Mikuni jets I installed in my TTR last year. It would not surprise me if 6 Sigma are branding/supplying Mikuni style jets for TTRs especially as the #52.5 pilot that you have is a odd Mikuni size (& is also the size specified in the Thumper Talk threads).

If I was using a Mikuni #52.5 pilot, it would be roughly ten sizes too large. Teikei jets do not have the same taper or flow rate as Mikuni. People have suggested that a Mikuni #42.5 would be the same as a Teikei #52.5 but this has not been confirmed yet. One thing that I can confirm is that the flow rates are different.

Jarrah

scotty72 · Veteran Member

Leak from carb

TTRfan · Super Guru

Petrol "creeps" and makes it difficult to track the source of a leak.

Have you disturbed the diaphragm cover (at the rear of the carb and held in by two screws and is shown in your pic looking suspiciously damp) as there are 2 little O rings under the cover that may need replacing.

Brian

scotty72 · Veteran Member

Hi Brian

It's been off and opened up 3 times in almost as many months so it's probably been disturbed at some point. Do you have the two o rings in stock and how much are they (would you be able to pop them in an envelope to save doubling the cost?!)? Is it worth changing any other o rings or seals while it's open again?

Thanks, Scott

TTRfan · Super Guru

I got a couple here that I can pop in the post. Is there anything else you need?

Brian