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

Terrence R · Senior Member

Float level maybe?

TT-R250M · Super Guru

The last thing I would suggest is to adjust the float level. It should never need adjustment unless you did not take care of it when you took it out.

It is hard to tell from the vague description of the problem but I would say that you are running too rich. Try to raise the jet needle clip position until it smooth's itself out. This may take more than one go at it.

Questions-

Does it pop or backfire upon deceleration in the mid-high range?

At what throttle range does it start happening, in more the mid range or high.

Any other symptoms?

Jarrah

Terrence R · Senior Member

It feels like once into the high revs that it just cuts out, like the killswitch is hit for 1-2 seconds, then runs, and then cuts out, then runs, then cuts out, etc... All in the high revs. I'm ganna pull the carb back out to take a look. Seems to me that it's taking all the fuel out of the bowl.
No popping and deacceleration, no signs of running lean. If it was too rich, wouldn't it be more if a "spuddering" sound at higher revs? This is literally cutting out.

TTRfan · Super Guru

Are the fuel lines and tap all clear and no blocked filter(s)? Open the float bowl drain screw and check you have a good flow of petrol. Best to extinguish all fags and naked flames first though wink

If all OK there, check the one-way valve in the filler cap is working and not vacuuming.

Two nice simple checks before pulling the carb biggrin

Brian

Terrence R · Senior Member

Jarrah, u were right. It was too rich. I put a 145 main in and it made a very noticeable difference. It'll now just spudder a bit if held wide open for an extended period. I may put in a 140, but I'm starting wonder if I over saturated my air filter with filter oil, which would maybe make it a bit rich? Cause oddly, according to the mods and elevation, my bike should require the 150 main.

Brain, I checked all lines and that filter that's in between the carb and near the bottom of the air box on the shifter side. Lots of clear fluid came out of the drain, like, LOTS! I heard of fluid coming out of there, but I didn't expect this much. It's was probably about 200-250 ml. Is that normal?

TT-R250M · Super Guru

I did not notice that you were in Canada when I first posted. I hope you know that the US/CA standard jetting is #50/#137. Therefore by rights you should only go up to a #52.5 and a #140 main jet.

If you upgrade all components a good rule of thumb is to go 2-2.5 sizes up on pilot and 2-3 sizes on main jet.

Oh, if you are talking about the drain as in the carburetor float bowl drain bolt, that much fuel would be perfectly normal if you still had the fuel line attatched.

Enjoy!

Jarrah

Terrence R · Senior Member

TT-R250M wrote:
I did not notice that you were in Canada when I first posted. I hope you know that the US/CA standard jetting is #50/#137. Therefore by rights you should only go up to a #52.5 and a #140 main jet.
If you upgrade all components a good rule of thumb is to go 2-2.5 sizes up on pilot and 2-3 sizes on main jet.
Oh, if you are talking about the drain as in the carburetor float bowl drain bolt, that much fuel would be perfectly normal.
Enjoy!
Jarrah

Ill put the 140 main in tomorrow. I may even put the needle clip back to the 3 position. The drain I'm talking about is on that filter that is between the carb and air box. It has a vent from the cylinder head and one to the airbox. I'm not even sure if it's a filter. All I know is that a lot fluid came out. Seemed liked watered down gas.

TT-R250M · Super Guru

Oh, you mean the water/oil separator. That is absolutely normal, water builds up from condensation and is transferred to the water/oil separator. You should drain it more often though. wink

There is another drain that should also be drained after every (long) ride, especially if crossing water. See part number(s) 28 and 16 here- http://www.partzilla.com/parts/search/Yamaha/Motorcycle/1999/TTR250LC/INTAKE/parts.html

Jarrah

TTRfan · Super Guru

Good advice as always from Jarrah.

A simple (and very unscientific) check on whether your mixture is too rich is to take the TTR for a run with the airbox cover off. If it runs better then it is an indicator that the mixture is too rch.

Brian

Terrence R · Senior Member

Just an update: I put the 140 main jet in and the bike seems to be running flawlessly. it was slightly rich on idle as it would start without the choke when cold. I had the fuel/air screw at 2 1/4 turns out, it's now set at 1 3/4 turns, which has made a bike difference 👍. Thanx.

Pics will be coming soon in the "show your bike" section!

-- Edited by Terrence R on Sunday 4th of May 2014 08:46:24 PM

TT-R250M · Super Guru

Glad you got it sorted!

Now that you have found the correct main jet, you may be able to get a bit more by adjusting the needle. If you think it is spot-on though, it may well be.

Enjoy!

Terrence R · Senior Member

Jarrah,

With my mods and being near sea elevation, what position would u recommend for my needle?

TT-R250M · Super Guru

Fine tuning the carburetor by adjusting the needle is not something that can be done over the internet. It is a matter of trial and error. At a guess I would say the middle or one down from the middle.

Start at the standard setting (the middle) and work your way down (moving the clip towards the sharp end) until you get a slight flat spot/splutter at high revs (WOT). Now raise the jet needle clip position two setting (towards the blunt end), this will be the optimal setting. If you do not get a flat spot at full throttle (or slow throttle response) when lowering the jet needle clip position, it suggests that you need a larger main jet (unlikely in your case).

Jarrah

Terrence R · Senior Member

This thread I started is a few weeks old now. Jarrah and Brian's input has helped me significantly. Thanx guys.

I put a few Kms on the ttr today. Seems to have a very minor slight popping on deacceleration. No big backfires or real noticeable pops, but enough for me to want address it. As I now have the 140 main jet and needle in the 4th position, I'm wondering if I should try the 145 main and the clip in maybe position #2. I'm just not too sure though because it was a bit spuddery on WOT with the 145 main, but the needle was also in the 4th position. What do u guys think? Would the 145 main jet still be too rich on WOT regardless of adjusting the needle? Or could the WOT circuit be mildly adjust by moving the needle clip?

TT-R250M · Super Guru

Terrence R wrote:
This thread I started is a few weeks old now. Jarrah and Brian's input has helped me significantly. Thanx guys.

I put a few Kms on the ttr today. Seems to have a very minor slight popping on deacceleration. No big backfires or real noticeable pops, but enough for me to want address it. As I now have the 140 main jet and needle in the 4th position, I'm wondering if I should try the 145 main and the clip in maybe position #2. I'm just not too sure though because it was a bit spuddery on WOT with the 145 main, but the needle was also in the 4th position. What do u guys think? Would the 145 main jet still be too rich on WOT regardless of adjusting the needle? Or could the WOT circuit be mildly adjust by moving the needle clip?

Thanks for the feedback and kind words Terrence.

I am not sure that I understand your question. You say that ''Seems to have a very minor slight popping on deceleration''. which is a rich symptom. You then say '' As I now have the 140 main jet and needle in the 4th position, I'm wondering if I should try the 145 main and the clip in maybe position #2.

I am wondering why you think using a larger main jet would solve the problem. Did you try raising the needle to the top position (closest to the blunt end)? If you did and it did not address your problem, you will need to go down to a #139 main jet (on roughly the middle position). However, I am unsure if a #139 main jet is available. Hopefully Brian can help with this.

Jarrah

Terrence R · Senior Member

Sorry, I meant " deacceleration". Meaning that it almost wants to backfire, but it not quite lean to backfire when releasing the throttle. Meaning it's slightly lean on top. It only does it if I left off the throttle completely after running wot. So, I'm wondering if I put a bigger main jet in, but lower the needle a couple positions, if I'll be ok. I just wasn't sure if adjusting the needle would help lean or richen the main jet circuit at all.

TT-R250M · Super Guru

You have totally confused me now-

To state the obvious, acceleration is when you first apply the throttle and the revs pick-up. Deceleration is when you are letting off the throttle and the engine winds down.

If you are getting popping/backfiring on acceleration (along with an overheating engine and other symptoms) it means that you are running lean. On the other hand, if you are getting popping on deceleration or it splutters at roughly 1/3 throttle, it suggests that you are running rich.

In this case you seem to be running rich but I will leave that for you to decide because as I said, I cannot understand the way you worded your post.

To be clear on the jet needle setting-

The jet needle clip positions are there in case you are in-between sizes. For example, if you have installed a #140 and it was slightly rich, but installing a #139 is too lean, you can adjust it by raising or lowering the main jet needle clip position. This helps to smooth out popping/backfiring from the fuel/air mixture being wrong. It will adjust a #139 jet to a #139.5 and also a #138.5. That is why there is no in-between sizes like pilot jets have (in various brands other than genuine Teikei).

In case you are unaware, there is more info on the carb here- http://ttr250.activeboard.com/t55374798/rebuilding-a-ttr250-teikei-y30p-carburettor/

Jarrah

TTRfan · Super Guru

TT-R250M wrote:
However, I am unsure if a #139 main jet is available. Hopefully Brian can help with this.

Can't find a #139 jet - sorry cry

Terrence R · Senior Member

This is also confusing me now because I'm sure that backfiring on deacceleration is a sign of a lean condition. I'm sure there's other threads that prove it. I'll take a look and post the links. I had many old four stroke 3 wheelers that would backfire or pop a bit ( almost backfiring). I easily sovled the problem by lifting the needle ( lowering the clip) which richened it. Isn't a rich condition recognized by spuddering on ACCELERATION?. There's been plenty discussed on if your motor is backfiring on DEACCELERATION, that it would need bigger jets and/or needle lifted ( clip lowered).

Terrence R · Senior Member

www.thumpertalk.com/topic/184550-ttr-250-backfiring/

www.xt225.com/forums/ubbthreads.php

TTRfan · Super Guru

As I mentioned earlier, a crude but quick and simple way to check for a rich mixture is to take off the airbox cover and see if it improves things. If it does then it indicates a rich mixture. The obverse is true i.e if it runs worse then maybe the mixture is too lean.

The TTR isn't prone to air leaks on the exhaust side so that's an unlikely cause of backfiring but what about the inlet stub between the carb and head? Are you sure yours is OK? The bonding between the rubber section and the aluminium part that bolts to the head can give up the ghost but that usually only happens on the older white TTRs.

Brian

TT-R250M · Super Guru

Terrence R wrote:
This is also confusing me now because I'm sure that backfiring on deacceleration is a sign of a lean condition. I'm sure there's other threads that prove it. I'll take a look and post the links. I had many old four stroke 3 wheelers that would backfire or pop a bit ( almost backfiring). I easily sovled the problem by lifting the needle ( lowering the clip) which richened it. Isn't a rich condition recognized by spuddering on ACCELERATION?. There's been plenty discussed on if your motor is backfiring on DEACCELERATION, that it would need bigger jets and/or needle lifted ( clip lowered).

You have no idea whatsoever..

If you are going to ignore my advice, good luck!

Jarrah

Terrence R · Senior Member

TT-R250M wrote:
Terrence R wrote:
This is also confusing me now because I'm sure that backfiring on deacceleration is a sign of a lean condition. I'm sure there's other threads that prove it. I'll take a look and post the links. I had many old four stroke 3 wheelers that would backfire or pop a bit ( almost backfiring). I easily sovled the problem by lifting the needle ( lowering the clip) which richened it. Isn't a rich condition recognized by spuddering on ACCELERATION?. There's been plenty discussed on if your motor is backfiring on DEACCELERATION, that it would need bigger jets and/or needle lifted ( clip lowered).
You have no idea whatsoever..
If you are going to ignore my advice, good luck!
Jarrah

I'm not ignoring your advise. I have no idea what so ever? I know for a fact that backfiring on deacceleration is from a lean condition. You think cause I'm asking a question about something means that I have zero knowledge on the subject? You're obviously ignoring the fact that u may be wrong in this discussion. I put links on that prove my argument. Don't get all upset because u can't except the fact that your advise is not helpful in this particular situation.

TT-R250M · Super Guru

Terrence R wrote:
TT-R250M wrote:
Terrence R wrote:
This is also confusing me now because I'm sure that backfiring on deacceleration is a sign of a lean condition. I'm sure there's other threads that prove it. I'll take a look and post the links. I had many old four stroke 3 wheelers that would backfire or pop a bit ( almost backfiring). I easily sovled the problem by lifting the needle ( lowering the clip) which richened it. Isn't a rich condition recognized by spuddering on ACCELERATION?. There's been plenty discussed on if your motor is backfiring on DEACCELERATION, that it would need bigger jets and/or needle lifted ( clip lowered).
You have no idea whatsoever..
If you are going to ignore my advice, good luck!
Jarrah
I'm not ignoring your advise. I have no idea what so ever? I know for a fact that backfiring on deacceleration is from a lean condition. You think cause I'm asking a question about something means that I have zero knowledge on the subject? You're obviously ignoring the fact that u may be wrong in this discussion. I put links on that prove my argument. Don't get all upset because u can't except the fact that your advise is not helpful in this particular situation.

Can't wait until you put the #145 main in. wink

I can't help that you don't know the difference between ''acceleration'' and deceleration. You seem to think it is deacceleration?? (spelling red lights on). Not to mention you cannot explain your problem clearly.

Good luck, you'll need it.

Jarrah

TT-R250M · Super Guru

Oh, the poster in ThumperTalk obviously has a blocked accelerator pump.

See here for more info-

http://ttr250.activeboard.com/t53839715/rough-running-no-mid-range-power-bogs-down-in-top-problem-fi/

http://ttr250.activeboard.com/t56226503/mid-rpm-range-bogs-down/

The second link is irrelevant as it is not a TTR250 and you will notice that they are talking more about pilot jets than main jets. However, since I have fixed the same problem on my mates XT225 I am going to suggest that the coast valve (AKA coast enrichener) is at fault. It will be blocked, leaking air from the O-ring, or the diaphragm is perished. The cover also breaks/cracks easily at the top. It stops the backfiring when you let off the throttle. See part number 6 below. I might add that the TTR250 does not have or need one and is a different beast.

Diagram of Yamaha Motorcycle Parts 1993 SEROW - XT225E CARBURETOR Diagram

Other things that I would suggest for both posters is that the air jets are blocked (and/or passages) or the fuel metering screw needs adjusting (or the O-ring is perished/flattened in the xt225's case).

You will notice on both threads that the OP did not find a solution. I would think that they would want to tell the world how GREAT it goes now after all that ''good'' advice >rolls eyes< .

There is a difference between a backfire and popping. A backfire indicates a lean condition, popping in the carb is due to a rich condition. People seem to confuse the two and it's where all the confusion starts.

I am not going to enter into your arguments as you do not have any info to argue with (Google is boring to argue with). I am no Google mechanic, as you can see, my knowledge comes from experience, not Google.

Google ''twits giving advice that does not work''. The threads you left will come up at the top of the list! biggrin biggrin biggrin

Jarrah

Terrence R · Senior Member

Just as an update,
I just got done riding the bike around after solving the problem. As I assumed, it was slightly lean on top. I raised the needle to its richest position and it now works better and has no popping on deceleration ( i'ld hate to spell that incorrectly). So it looks like the google twits were also right in this situation. Maybe it was the way I was explaining it that caused your confusion jarrah, but I don't think that there was any other way to explain it. Either way, it was lean, it's now solved, and I hope that's there's no hard feelings.

TT-R250M · Super Guru

So it didn't need the #145 after all that.

All I can say is that either your explaining skills need work or your bike is SO much different from mine.

If you want to believe Google mechanics you go right ahead. It is just a coincidence (or in your head) that anything from those links worked as none of them address needle clip position.

If I ever have to help you again, remind me to shoot myself! wink

Jarrah

-- Edited by TT-R250M on Tuesday 20th of May 2014 04:34:06 PM

Terrence R · Senior Member

wink Lol. All I was trying to say about putting the 145 main is that I could've put it in and lowered the needle to help compensate for the bigger main jet. That was actually my question. Because of it almost wanting to backfire, I knew it was a slight lean condition. I'll try to explain in better detail next time I ask any questions on here. wink Thanx

Terrence R · Senior Member

We were discussing if it was lean, or if it was rich. U assumed it was rich, I assumed it was lean. It was lean. Problem solved. The links I posted were to just indicate the lean popping symtoms that I was having. Thanx for your input though.

TT-R250M · Super Guru

It is now that I might remind you that without me you would still have the #150 installed and swearing that it was the float height too low (or still trying to adjust it).

As I said, backfiring/popping can be caused by either a rich or lean condition and can be confused easily, especially when you are trying to fix something over the internet. More info than ''backfiring'' or ''popping'' is needed as it's not like I can take it for a test ride.

Thanks for appreciating the time I spent, even if most of it was ignored.

Jarrah

Ps. when you say '' I raised the needle to its richest position'' does that mean that you lowered the clip position (towards the sharp end) or raised it (towards the blunt end)?

Terrence R · Senior Member

I raised the needle by putting the clip in position #5, which is closest to the sharp end. Which richens it if was too lean. The blue line on your needle adjustment diagram can be used as a reference.

TT-R250M · Super Guru

So you mean to say that you moved it one position and it stopped backfiring? I find that VERY hard to believe but anyway, if the problem is solved it's solved, any way you want to look at it (thank the lord).

I still think you should have taken my original advice to save all this confusion...

TT-R250M wrote:
I did not notice that you were in Canada when I first posted. I hope you know that the US/CA standard jetting is #50/#137. Therefore by rights you should only go up to a #52.5 and a #140 main jet.
If you upgrade all components a good rule of thumb is to go 2-2.5 sizes up on pilot and 2-3 sizes on main jet.
Oh, if you are talking about the drain as in the carburetor float bowl drain bolt, that much fuel would be perfectly normal if you still had the fuel line attatched.
Enjoy!
Jarrah

TT-R250M wrote:
Fine tuning the carburetor by adjusting the needle is not something that can be done over the internet. It is a matter of trial and error. At a guess I would say the middle or one down from the middle.
Start at the standard setting (the middle) and work your way down (moving the clip towards the sharp end) until you get a slight flat spot/splutter at high revs (WOT). Now raise the jet needle clip position two setting (towards the blunt end), this will be the optimal setting. If you do not get a flat spot at full throttle (or slow throttle response) when lowering the jet needle clip position, it suggests that you need a larger main jet (unlikely in your case).
Jarrah

Glad this thread is at an end is all I can say at the end of it all.

Jarrah

Yuraku · Veteran Member

TT-R250M wrote:
If I ever have to help you again, remind me to shoot myself!
Jarrah

-- Edited by TT-R250M on Tuesday 20th of May 2014 04:34:06 PM

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