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

TT-R250M · Super Guru

Rebuilding a TTR250 Teikei Y30P Carburettor

TTRfan · Super Guru

Excellent update to an already brilliant thread Jarrah! It's definitely a sticky wink

Cheers

Brian

Flying Dodo · Veteran Member

Hi All
Am having a bit of a problem with my bike - it runs reasonably well but after throttle close down and low revs - junctions, downhills roundabouts etc when I open it up it hesitates a lot and then goes. I've stripped the bottom end of the carb and cleaned it with air and solvent but as yet to no avail, When looking at the accelerator pump nozzle I noted that it squirts fuel towards the side of the carb not into the center, (using the method below) so not straight down the barrel - is this likely to be the nozzle out of line and can I turn it or is it just a partly blocked nozzle or normal? Have tried air and solvents but not yet the wire methods. Any help appreciated. I quote Jarrah's accelerator pump notes from above below to try to explain what I'm getting at
Thanks Dave

Checking the Accelerator Pump
Before dismantling the carburetor, it is advisable to check that the accelerator pump is working correctly. I should advise you now that petrol is not good for your eyes so be CAREFUL! 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 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 the diaphragm and all O-rings.
553027_562393563794119_1622177328_n.jpg

TT-R250M · Super Guru

Hey Dave,

As long as there is a nice stream of fuel, the accelerator pump nozzle should be fine. It does not squirt directly into the intake, rather against the carb throttle body IYKWIM. I would NOT try to turn it as it is a press fit!

As your profile suggests that you are in France and your profile picture seems to be up on a mountain, I would suggest to move the main jet needle position 1~2 settings towards the leaner position(s). It seems to be your problem, however without more info I can't be sure.

Also make sure that your fuel metering screw is between 1 1/2 ~ 2 1/2 turns out from fully seated (as mentioned above).

Does the problem happen from idle to 1/3 throttle? or at or after 1/3 throttle?

Any other symptoms?

It would be helpful to know what jets are fitted, elevation, mods, climate also.

Cheers!

Jarrah

Flying Dodo · Veteran Member

TT-R250M wrote:
Hey Dave,
As long as there is a nice stream of fuel, the accelerator pump nozzle should be fine. It does not squirt directly into the intake, rather against the carb throttle body IYKWIM. I would NOT try to turn it as it is a press fit!
As your profile suggests that you are in France and your profile picture seems to be up on a mountain, I would suggest to move the main jet needle position 1~2 settings towards the leaner position(s). It seems to be your problem, however without more info I can't be sure.
Also make sure that your fuel metering screw is between 1 1/2 ~ 2 1/2 turns out from fully seated (as mentioned above).
Does the problem happen from idle to 1/3 throttle? or at or after 1/3 throttle?
Any other symptoms?
It would be helpful to know what jets are fitted, elevation, mods, climate also.
Cheers!
Jarrah

Hi Jarrah

It's all standard jets and air intakes, problem is from zero to 1/3 throttle and only when revs have dropped on deceleration, I'm at 600m - 2000ft valley bottom and this is happening at this altitude as well as higher up in the hills. Screw is set at 2 turns but have tried it at everything from 1 1/4 to 3 without solving this problem.

Cheers

Dave

Flying Dodo · Veteran Member

Padowan wrote:
My accelerator pump nozzle also exits towards the wall of the carb, so I don't think it's unusual. From an operational perspective I expect the air speed flowing along the walls is high enough during an induction stroke to pull that fuel through the carb, even on tick over.

I coukd do some sums to work it out, but even at around 1200rpm (for ease of maths) that's 10 intake cycles per second or 2.5lt/sec of air being drawn in, through an orifice of about 30 mm across, (about 7cm2) assuming linear flow that'll mean it's moving at 3.5 metres per second.

Edit: Actually it's twice that speed as the intakes are happening on every other stroke.

-- Edited by Padowan on Monday 16th of June 2014 03:28:25 PM

-- Edited by Padowan on Monday 16th of June 2014 03:29:46 PM

Thanks - at least that rules out that one and I'm glad i didn't try to force the jet round!

Dave

TT-R250M · Super Guru

Flying Dodo wrote:
Hi Jarrah
It's all standard jets and air intakes, problem is from zero to 1/3 throttle and only when revs have dropped on deceleration, I'm at 600m - 2000ft valley bottom and this is happening at this altitude as well as higher up in the hills. Screw is set at 2 turns but have tried it at everything from 1 1/4 to 3 without solving this problem.
Cheers
Dave

Your problem could be either-

The main jet is slightly rich causing it to stumble when the throttle is let off quickly and applied again.

The pilot jet is partially blocked or varnished.

The air jets are partially blocked.

Air-filter needs cleaning.

Wrong idle speed.

Partially blocked needle and seat (AKA float needle valve).

Incorrect float height (not likely unless it has not been taken care of.

Accelerator pump return spring faulty (or not installed).

Diaphragm return spring faulty.

Spark plug gap.

Electrical problem (not very likely).

Fuel metering O-ring perished.

Things to try-

Move the jet needle clip position towards the leaner setting 1 ~ 2 settings.

Take the air filter side cover off to see if it helps.

If you can let me know a little more about your problem, I may be able to help to eliminate some of the possible causes.

Good luck!

Jarrah

AGman · Veteran Member

Great post Jarrah.

The only thing I would add is in the tool section to use JIS (Japanese Industrial Standard) Philips head screwdrivers if possible. You will see the small indent in the head of the screw heads - this specifies they are JIS. They make a big difference and you wont chew out the heads of the screws.

I realise it makes it a pain for us that only touch the carb once in a blue moon but I thought I would bring it up. Everyone blames the poor materials used in Japanese carbys, but it is the screw standard, not the material.

Flying Dodo · Veteran Member

TT-R250M wrote:
Flying Dodo wrote:
Hi Jarrah
It's all standard jets and air intakes, problem is from zero to 1/3 throttle and only when revs have dropped on deceleration, I'm at 600m - 2000ft valley bottom and this is happening at this altitude as well as higher up in the hills. Screw is set at 2 turns but have tried it at everything from 1 1/4 to 3 without solving this problem.
Cheers
Dave
Your problem could be either-
The main jet is slightly rich causing it to stumble when the throttle is let off quickly and applied again. - It's more when throttle left off on deceleration to low revs and then applied rather than sudden shut off?
The pilot jet is partially blocked or varnished. - Have cleaned this several times - next step maybe to order and replace jets
The air jets are partially blocked. - Again have tried to clean thoroughly and otherwise it runs OK
Air-filter needs cleaning. - cleaned and re oiled within last week
Wrong idle speed. - I think this is OK and it idles fine.
Partially blocked needle and seat (AKA float needle valve).
Incorrect float height (not likely unless it has not been taken care of. - Didn't think this mattered too much so will re check.
Accelerator pump return spring faulty (or not installed). - Checked OK
Diaphragm return spring faulty. - checked OK
Spark plug gap. checked OK
Electrical problem (not very likely). Don't think so or it wouldn't be so specific?
Fuel metering O-ring perished. All O rings OK though side cover one a bit flat!
Things to try-
Move the jet needle clip position towards the leaner setting 1 ~ 2 settings. Will try to do this today!
Take the air filter side cover off to see if it helps. Maybe I'll try this first.

If you can let me know a little more about your problem, I may be able to help to eliminate some of the possible causes.
Good luck!
Jarrah

Thanks Jarrah for a very comprehensive answer - will try leaning the mixture a couple of stops - have made notes against your suggestions above which may?? help explain it clearer

Ta David

TT-R250M · Super Guru

Hey David,

I think your problem is the side cover O-ring. It should not be flat and needs to seal or you will get the symptoms that you described. The only other possibility is that the pilot jet is varnished (but not that likely) or loose. The airway could also be blocked so it may be worth blowing compressed air through the fuel metering screw passage (after taking the fuel metering screw and spring out of course).

I would buy the fuel metering screw set at the same time to be sure the fuel metering O-ring is sealing correctly, it should be cheap enough.

Link to parts in the US

Good luck, let me know how you go.

Jarrah

TTRfan · Super Guru

Slightly off topic but may be of interest.

I recently fitted a carb to a TTR and forgot to adjust the pilot screw and left it fully closed.

The TTR started and ran absolutely fine and ticked over no problem confuse

Now adjusted wink

Brian

Flying Dodo · Veteran Member

Hmm, just leaned it - raising the collar from it's middle setting where it was to the top - now tends to stall after running when on idle as if starved of fuel or air (idles OK when stood) - only been for a short run - will try it further this afternoon then maybe try the needle the other way (full rich) - will at least give you guys who understand these things some stuff to work on in the hope you can solve it for me!!
Thanks again
Dave

Flying Dodo · Veteran Member

TTRfan wrote:
Slightly off topic but may be of interest.
I recently fitted a carb to a TTR and forgot to adjust the pilot screw and left it fully closed.
The TTR started and ran absolutely fine and ticked over no problem
Now adjusted
Brian

Thanks Brian - Will maybe try a range of pilot screw positions when I run out this afternoon. Cheers Dave

TT-R250M · Super Guru

TTRfan wrote:
Slightly off topic but may be of interest.
I recently fitted a carb to a TTR and forgot to adjust the pilot screw and left it fully closed.
The TTR started and ran absolutely fine and ticked over no problem
Now adjusted
Brian

Just pointing out that if the screw can be turned all the way in without the engine stalling, a smaller pilot jet is required. It could also mean that the the pilot air jet is partially blocked or the side cover seal is not sealing. Either way, something is not right.

Jarrah

Flying Dodo · Veteran Member

Hi All
Well took it out with the leaner setting and it was a disaster (except at tickover???) - wouldn't run without choke, stalled, hesitated and in the end had to set 90% choke to get it to run anywhere - without choke was missing and hiccuping at up to 60% throttle - but OK at WOT and stalled as soon as throttle closed out of gear.
Have gone for the opposite setting on needle - 2 stops down from centre to see what happens - sadly rain (well thunder and lightening) has stopped play for the day so will try a run out tomorrow morning and let you know the results.
Sorry Jarrah missed your post re the flat o ring - will check the assorted o ring box and see if there's one that'll fit. If this doesn't work then will abandon for the moment and replace the jets and remaining o rings and gaskets later in the summer as work now becons! Will let you know anyway.
Thanks
Dave

TT-R250M · Super Guru

Sounds like some progress has been made.

If raising the jet needle produced that result, I would say that the lower setting would be better for you. A bit of playing around with it and you should get it perfect. The reason I asked you to raise is to eliminate the possibility of running rich on main jet( it effects low revs as well as high if rich). With that possibility ruled out it is fair to say that your problem lies with the side cover O-ring. However, it still could be the pilot jet varnished, the pilot air jet or passage blocked.

The O-ring is more of a special seal than an O-ring but the right size O-ring might suffice.

Jarrah

Flying Dodo · Veteran Member

Hi Jarrah
Have put an O ring the right size in for now (I've kept the seal) as its easy to swap back and if it ever stops raining I'll go out and give it a try - looking like tomorrow now though.
But do feel progress is being made - we'll see tomorrow.
Thanks for the help - I'll let you know.
Dave

TT-R250M · Super Guru

Just to verify the first picture in my last post- the blue lines represents the pilot air passages- these MUST be spotless!

The more possible causes that you eliminate, the more chance you have of finding the problem so not finding the problem can be a good thing. smile

I'll be waiting on the update (go away rain!). wink

Jarrah

TTRfan · Super Guru

Your knowledge of the TTR carb is amazing Jarrah! Thanks you for sharing - the pics are priceless.

Brian

TT-R250M · Super Guru

TTRfan wrote:
Your knowledge of the TTR carb is amazing Jarrah! Thanks you for sharing - the pics are priceless.
Brian

Thanks Brian,

I am going to add how to check the float height using both methods stated in the manual. It is not very clear on the difference between the float height and the fuel height, I intend to make it VERY clear, stay tuned! wink

AGman wrote:
Great post Jarrah.

The only thing I would add is in the tool section to use JIS (Japanese Industrial Standard) Philips head screwdrivers if possible. You will see the small indent in the head of the screw heads - this specifies they are JIS. They make a big difference and you wont chew out the heads of the screws.

I realise it makes it a pain for us that only touch the carb once in a blue moon but I thought I would bring it up. Everyone blames the poor materials used in Japanese carbys, but it is the screw standard, not the material.

Thanks Agman and point taken, you may notice the change. If you have any more suggestions, please don't refrain from posting them. It was a lot of typing but I am pretty sure it is okay now? smile

Enjoy!

Jarrah

Flying Dodo · Veteran Member

Update - took it out this morning and the hesitation at low revs is cured - hooray! Need some more fiddling as there's a bit of a bogging down at around half throttle and struggling to get the tickover right it wants to die or over rev but loads better than before I started which was driving me nuts; it also now goes like a bomb at WOT - thanks all - will maybe try the next up from maximum rich on the needle to see if that's the best compromise but that may have to wait till i've got more time to fiddle - unless it rains again this afternoon!!
Thanks all and especially Jarrah for the tips and encouragement.
Dave

TT-R250M · Super Guru

Hey Dave,

You have the right idea, move the clip to setting two from the sharp end and it should be good.

Amazing how much difference it makes dialing the needle in. aww

Glad you got it sorted!

Jarrah

TTRfan · Super Guru

Your post was amazing Jarrah but not so good now that most of the photos aren't loading. Any chance of restoring them please?

Thanks in advance.

Brian

TTRfan · Super Guru

Most of the new parts, gaskets, O rings, jets, etc., that might be needed are available next day for UK owners from here - nothing on back order - all on the shelf wink

We post abroad but obviously the parts will take longer to arrive.

Brian

DC · Veteran Member

Refurb a TTR250 Teikei Y30P Carburettor

Magilla · Member

RE: Rebuilding a TTR250 Teikei Y30P Carburettor

TTRfan · Super Guru

Correct!

Carb float pin removal.jpg

But the manual also says:

Carb float pin installation.jpg

zzrdd · Member

Good info guys. Here's my carb challenge with my 2002 TTR 250

Altitude: 7500-8500 feet (2300-2600 meters, moderate temps <80F (<27C)
Main Jet = 128
Pilot = 50
Needle = 5C9C
Needle position = 2nd slot from leanest (two slots down from the top/most lean slot).
Accelerator pump = new diaphragm and post. Squirts fuel like it should.
Mixture screw: out 1.75 - 2.75 turns (seems little difference)

Airbox = OEM not modified

Exhaust pipe = stock w/baffle removed.

Carb cleaned all orifices open, engine rebuilt, good compression. Runs strong and starts well cold (choke hardly needed) and hot. Runs well from idle to WOT. Pulls reasonably strong.

ISSUE: After WOT for a bit, when the throttle is reduced, the engine stumbles. (I assumed main jet rich or lean?)
Also, on whoops (closely spaced 2-3 foot bumps at moderate speed standing on pegs), the bike stumbles (carb bowl splash?). Carb bowl has plastic piece installed around main jet location. (bowl level too low?, seems odd if rich).

Spark plug is lightly sooty (black) after WOT then kill switch and coast to the garage (I suspected the main jet was too rich and was testing WOT rich/lean condition).

Based on the spark plug color (black and slightly sooty), easy start cold w/little choke, I assuming too rich, therefore:

Attempt #1: Leaned needle one slot to leanest position = top slot. Result: Poor idle, poor running.

Odd: Spark plug says too rich but when we leaned the needle, engine was not happy.
Weird: I did not expect the needle to impact idle and <1/3 throttle (much).

What should I try next? Many thanks.

Rick

Colorado Springs, CO

PS Posting this in a couple of places as I am not sure about traffic. Kindly excuse the duplicate posts.

-- Edited by zzrdd on Tuesday 11th of August 2015 09:20:43 PM

jpv7774 · Member

Crap....!!!!!! He warned me....in all caps.........Dismantling my carb tonight......got to the float pin....was being unbelievably gentle as to not break the damn posts! I had the pin 97percent out and here is what I believe happened.

I was using a nail as my punch.....I had pin almost out but my nail was going through both holes to keep it straight......I guess on my last hit with float already removed......I made the strike w my hammer...it hit the nail which broke the pin free.....but I guess the nail was so short that my hammer hit the first post breaking it off clean. Man was I pissed. Oh well.....gotta move forward. I think JB Weld should work......anybody try this yet?

TTRfan · Super Guru

Removing the float pin safely - see

The tool is available in Halfords - see here.

Thanks to Mike for the links biggrin

Brian

pug · Guru

Like that top tip I would never have thought of using the punch for that and should the need arise in just happen to have one in my Engineers box so thanks

Mike an brian for the tip

-- Edited by pug on Thursday 14th of January 2016 01:16:11 PM

peteBLUEttr · Super Guru

Yeah handy that. Takes the stress off it. Smart tip! biggrin

locky · Guru

I have one in my tool kit. Great idea.

JOHNYBOY · Super Guru

been stripping carbs down for years broke many pin posts never thought of that good idea just ordered one of those punches cheers great forum this we all think we know it all you are never too old to learn

Trask · Member

Checking the Accelerator Pump
Before dismantling the carburetor, it is advisable to check that the accelerator pump is working correctly. I should advise you now that petrol is not good for your eyes so be CAREFUL! 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 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 the diaphragm and all O-rings.

Response to this..

What would be the result, or how would the bike run if it were clogged? Any thing helps!

TTRfan · Super Guru

Trask wrote:
Checking the Accelerator Pump
snip..

Response to this..

What would be the result, or how would the bike run if it were clogged? Any thing helps!

The accelerator pump makes the TTR more lively by squirting in the extra go juice when the throttle is cracked open.

The engine response would be noticeably "flatter" if the accelerator pump wasn't working.

TTRfan · Super Guru

I tried repairing Jarrah's original post back along by putting in some of my own photos etc but there were still quite a few missing plus it's difficult getting inside someone else's head to get their meaning on occasions.

Anyways up, I have been refurbishing and repairing carbs over the past few months so have amassed some experience and a lot of new photos so I have had a go at building my own pictorial guide and would be grateful for feedback and, particularly, constructive criticism and suggestions for improvement.

See http://ttr250.com/Carb/TTR250_carburettor_strip_and_rebuild_guide.htm

Brian

ssiddall · Newbie

jpv7774 wrote:
Crap....!!!!!! He warned me....in all caps.........Dismantling my carb tonight......got to the float pin....was being unbelievably gentle as to not break the damn posts! I had the pin 97percent out and here is what I believe happened.
I was using a nail as my punch.....I had pin almost out but my nail was going through both holes to keep it straight......I guess on my last hit with float already removed......I made the strike w my hammer...it hit the nail which broke the pin free.....but I guess the nail was so short that my hammer hit the first post breaking it off clean. Man was I pissed. Oh well.....gotta move forward. I think JB Weld should work......anybody try this yet?

I too just broke one of the posts off trying to remove the float pin. Also trying JB Weld. Did it work for you?

KevRed · Member

Thats what i used to repair mine ..

mossproof · Super Guru

This is a much neater solution, and no risk of the float coming adrift without you knowing, possibly flooding the engine and sump, with fuel:

www.ttr250.com/Floatpost/TTR_float_post_repair.htm

scam · Newbie

Hi, I'm a carb beginner and hoping for some help please if possible.

I could quote the post above by DC almost verbatum, having left (??) my bike with fuel in the carb for > 1 year and then only able to fire up with ether but not run. It was heavily coated on the surfaces in the float chamber and the needles/jets therein were mostly bblocked. I have cleaned them with carb cleaner and soft wire + compressed air, but still cannot get the bike to run other than at idle.

I hope DC doesn't mind if I borrowed his image. I have so far avoided removing the float as I dont have an automatic centre punch and I worry about breaking the posts.

I cannot see the fuel jet from the accelerator pump nozzle, however the diaphragm appears intact and supple.
I have blasted the accelerator pump nozzle from beneath with compressed air and fed soft wire all the way up its length, but still no fuel jet.

Also, there is a passageway between the diaphragm chamber and the inside of the float bowl with what seems to be a ball valve in it; I have circled and arrowed it on my copy of DC's photo. The orifaces to this were caked in gum both sides, which I have removed with carb cleaner and friction, but I still cannot blow air through it (tried both directions) and I am worried about damaging the ball or it's housing if I try to poke through some wire.

Could someone please advise:
a) what else can I do to produce the fuel jet from the accelerator pump nozzle? (I am thinking to replace the diaphragm regardless of its apparent good condition, but it is not in stock on totallyttr's site and where I am in Australia there are no local stockists).

b) What is the name of the passage I have circled in red in the image? Do I have to buy a whole new bowl if I cannot un-jam it?
There does not appear to be a part number for the float bowl cover so might I need to buy a complete carb assembly if this cannot be unblocked (AUD$621)?

c) How do I clean the air jets (pilot and main) other than by compressed air into them (can I access the other end and feed wire through)?

What am I missing, should I pull down the top end of the carb as well? Something else?

Thanks in advance.
Regards,
Cam

miltos · Member

Many thanks for all the card rebuilding stuf. Assembling the carb about 15 months after getting it in pieces, it has been a very helpful content.

Just for improvement of this guide, I would like to inform that I was struggling a bit due to a wrong mention at one end of the throttle lever spring at the following photo
ttr250.com/Carb/Throttle_return_spring.jpg

The correct location of the spring ends can be found at the last photo of the guide
ttr250.com/Carb/New_carb1.jpg

-- Edited by miltos on Tuesday 23rd of March 2021 09:47:59 AM

TTRfan · Super Guru

miltos wrote:
Many thanks for all the card rebuilding stuf. Assembling the carb about 15 months after getting it in pieces, it has been a very helpful content.

Just for improvement of this guide, I would like to inform that I was struggling a bit due to a wrong mention at one end of the throttle lever spring at the following photo
ttr250.com/Carb/Throttle_return_spring.jpg

The correct location of the spring ends can be found at the last photo of the guide
ttr250.com/Carb/New_carb1.jpg

Well spotted - you are dead right and the photo is wrong - sorry disbelief

I have amended the web page and it should be OK now.

Many thanks for the feedback wink

Brian

charrito · Member

Hello all, done a bit of searching and can't find anyone being able to remove the float needle valve/seat. I do have a replacement but the one that's in the carb is really stuck in there. I have it soaking in WD40 to see if that helps. Any other suggestions?

Edit: I did find a post about this, but till need the question answered. Looks like I pretty much have to break the old one out?

-- Edited by charrito on Sunday 3rd of April 2022 06:24:51 PM