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

Here's some background waffle on engine exhaust gas temperature (EGT) in case anyone has an interest.
It is not meant to be advice on overcoming (or achieving) header pipe heating in TTR250s but could help with understanding.
[disclaimer: it could be only half the truth, check with a thermodynamics expert].

First an observation that the two main things that affect EGT are ignition advance and fuel mixture.
The safest thing to change is mixture and the safest mixture change is to go rich.

What causes heat is of course burning of fuel in the presence of oxygen from the air.
The amount of oxygen is determined by the amount of air let in by the throttle.
The amount of fuel in that air is determined by jet sizes etc (yeah, yeah, obvious, I know!).

The most energy that can be extracted is when there is just enough fuel for all the oxygen to be consumed in the fuel burn.
This sweet point of complete combustion is theoretically at a ratio of 14.7 air to fuel (or lambda = 1.0).
At this "stoichiometric point", all the fuel is turned into water and carbon dioxide (go greenhouse!).
The exhaust gas contains this plus nitrogen (plus a few nasties, if we are talking real world instead of theory).

This point of complete combustion also gives the highest EGT (yep, complete burning is hottest).

If you lean out the mixture from this peak, the EGT drops (because there is less fuel, there is less energy).
If you richen the mixture from this peak, the EGT also drops. The reason for this drop in EGT is a little more complicated -
related to the fact that the unburnt fuel has more "degrees of freedom", and to the "equipartition of energy".

Look up the kinetic theory of gases if you are interested, but it really does not matter - just note that
going EITHER rich or lean from this magic point will drop the EGT.

Now here are the interesting practical jetting consequences..

1. if you go very slightly leaner than this maximum EGT point you get best economy (but watch out for pinging);
2. if you go a bit richer than this maximum EGT point you get best power, in practice;
3. usually a standard factory jetting is even richer (and so cooler EGT) than the maximum power point.

The last point explains why people often say "leaner is hotter" (as it depends on the starting point).
To account for fuel, temperature, altitude variations, manufacturers of simple carb engines err on the rich side.
So from STANDARD, going slightly leaner usually means a hotter exhaust, but a bit more power (AND economy!).

Race tuners often use peak EGT as a handy reference point. If you go "lean of peak" (as the tuners say),
you will be running cooler (and same if you go "rich of peak", which is the usual case).

The actual EGT can only be known if you have a good sensor installed, but it can safely go as high as 1400F to 1500F.
This EGT is not the same as cylinder head temperature, which is much much lower.
It is not EGT which kills motors, but detonation.
(when detonation happens, EGT actually goes down!).
However at continuous high load (the zone controlled by the main jet), the high power and high temperature operation can lead to climbing oil and cylinder head temperatures, which are not good for long life.  A plug check at maximum power may be the best way to check this.   

The EGT will be roughly the same, regardless of throttle opening and rpm (but only with proper ignition and jetting).
However there are often irregularities at cold engine start, and at idle, where fuel metering is imprecise,
and exhaust resonaces can have compounding effects at certain rpm.

Motorcycles like the TTR don't have EGT sensors, but the color of the hot header pipe is a kind of crude sensor.
The header pipe won't be hotter than the EGT but it will get very close.
If the exhaust pulses are more frequent (higher revs) or have more volume (bigger throttle opening),
and if the exhaust header is not well air cooled (stationary running) and is thin steel,
then the exhaust will transfer a lot of heat at a high rate to the header
and it will EASILY reach an equilibrium temperature close to EGT.

The header temperature can be very roughly guaged by eye (if you are a good blacksmith).
Higher temperature colors can be seen in daylight, but rarely in full direct sunlight.

1100F is brown red (you probably need it to be very dark to see this color)
1200F is blood red
1300F is dark cherry
1400F is cherry
1500F is light cherry

Also note that the header can retain a permanent discoloration, different to the above, often a blue/purple.
This happens to stainless steel at quite low temperatures (artist do it for effect) and is related
to the type of stainless steel and the surface oxidation, and is of no real significance.

What is the optimum EGT for a Yamaha, and should we worry about a slight header glow?

I have absolutely no idea, but I'm not worried about my own bike.
But if it suddenly started to get a very obvious header glow which is more than I had seen before,
I would start scratching my head and wondering about the ignition control circuitry and stuff.

I hope this lengthy post has at least amused some of you who read this far

[postscript: I am just presenting background information, not prescribing anything. jetting changes should always be made in small increments, usually trying rich first, taking into account temperature, elevation and riding style, with the presumption that standard is probably best, and noting all the effects carefully and taking plug readings. I am certainly not advocating a mindless policy of "just go leaner" (OR richer).]

-- Edited by brindabella on Thursday 21st of February 2013 04:40:05 AM

At last we have a sensible response.

Thank you for your well written, succinct and understandable reply in plain English, Mr. B.  

I think this thread has just about been thrashed to death and taken round the houses; but you've nailed it with that response.

At least LRJ has now had enough answers on which to work to rectify his TTR's running.

A simpler answer would be to not go out at night - just ride the bike in daylight only.

Martyn

 

Well, I think that I am ready to update the story of the glowing header.

I ordered the larger main jets, but they took over a week to arrive. So, in the mean time, I tried a few experiments: 1. I removed the silencer insert from the end of the muffler (I think the NA set up is different than Aussie/NZ/UK/SA mufflers) for more airflow to see the effect of running a bit leaner. Result was that it ran crappy and the header glowed. Was worse with the cover off the air box. (No surprise, there.) 2. I covered up half the snorkel to reduce air flow, to try and have it run richer. The result was it ran even crappier than when it was lean, and the header still glowed! Granted, covering the snorkel is not the same as having a larger main jet, but I was surprised at the result.

Then, a friend said that his mechanic, when told of my issue, told him that he had fixed this problem before with other bikes. When I spoke to him, he talked about needing to check the timing and the cams, after double-checking the usual issues of valve clearances, etc. He took the bike and went over it carefully. In the end, the timing was spot-on, the compression was 170 psi, and everything else checked out. The bike runs beautifully, but it still glows. He called it an "enigma". He noted, though, that a stainless steel exhaust pipe should tarnish to a bronzy-gold color if the temperature is correct, but it turns to blue if it is too hot. My pipe is gold everywhere, but right by the engine, where it is blue. In examining as many photos as I could online, I noticed that the few North American bikes that had stock exhaust systems (with photos that showed the header pipe near the engine), had blue-colored headers, like mine. All the British, Australian, and South African bikes (larger pilot and main jets as stock) that I could see had gold pipes right up to the engine. It would make sense that Jarrah's assertion that the bike needs larger jets is correct. As the glow on my bike is quite obvious at 1/8 throttle, it would seem that a larger pilot jet might be the first place to start.

However, I also called two other advertised Yamaha mechanics (One at a dealership, the other independent). After hearing all the facts, they both said to not worry about it and just ride it. One of the two said that he sees this situation in lots of bikes, and it is pretty normal for many bikes.

I still felt kind of uncomfortable about having a glowing header, though. Opinion on the subject online among American enthusiasts is highly divided. Clearly the larger jetted bikes in other countries don't run so hot. Then I noticed that my trusty xt-225 (My main daily commuter.) also has blue coloring on the pipe next to the engine. It is a lot harder to see the header on that bike while you are riding, but I made the effort while riding to work early this morning, and saw that it, too, was glowing. It didn't seem to be glowing quite as bright as the TTR, but the signal lights are set out farther and are brighter than the ones I have on the TTR. This xt-225 is also stock, except the needle has been shimmed a small bit, and it runs like a dream.

As I said, I believe that Jarrah is probably correct in saying that larger jets would probably solve the glowing issue. At this point, though, I am not sure that it is worthwhile to experiment further with putting in different jets, and then figuring out how to tune the bike so that it will run properly with the current stock exhaust, etc. I would have to continue to pay mechanics to do this for me, because I really don't have the experience/training to do this myself.

Sorry for such a wordy contribution, but that is the whole story, up to this point. I am very grateful for everyone who contributed their knowledge and expertise. This has been a good education for me.

Larry

It's possible that you didn't read the part where it says ''I think Jarrah is right''.

I am yet to see the day (or night for that matter) that my header pipe glows from a rich condition. In fact, this will never happen :) However, I have already seen the day (night to be correct) that it got hot at the header pipe from running lean.

Oh, I will say it again; this is NOT from running rich lol, it is NOT possible without the bike running like cr@p! Even when running that rich that it runs bad, splutters, backfires on decel, un-burnt fuel smell, black plug etc.. it has not caused this to happen EVER!

All said & done; at least my bike is running right after 1500 KM (even though slightly rich).

ps. You like RED header pipes that turn blue; , I like a COOL header pipes that turn to gold;

 

 

I do remember, Brian. One day, though, I want try to try changing those jets, and see what happens.

Some people on this forum seem to believe that it is normal- let me tell you, it is NOT!

At no time should the header become red (even at night), unless left to idle for longer than 15-20 mins. This condition is caused by a lean condition, either pilot jet or main jet, depending on when it gets red. If it gets red while at wide open throttle but gets better when running just under an idle it suggests that your main jet is too small or your main jet needle is not adjusted properly. If it gets red at idle and up to 1/3 throttle but gets better when at full throttle it suggests that the pilot jet needs to be larger. If it happens constantly at any rev range it suggests that they are both too small.

Of course there are other things that will make it overheat like- air flow hole in cylinder head blocked, valves not sealing, accelerator pump not working correctly or too much backpressure (if aftermarket exhaust is fitted or it has been repacked too much) etc. However, it is more likely to be from a lean condition.

Does it happen when at full throttle, idle to 1/3 throttle or both?

Jarrah

 

Not normal dude and may result in some expensive damage, have a little spray with some carb cleaner or wd40 around all the carb fittings and seals to make sure your not sucking in air. If the revs pick up as you are spraying then you know its sucking air. Also check if the air filter is seating correctly.
Easy things first :)

TTRfan wrote:

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comeragh wrote:

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I wouldnt advise fixing this glowing pipe if u are a smoker .
Have been out on many a late night bike ride and forgotten my lighter .
The glowing pipe will light a rolly or cig if held just of idle for a few seconds .
A very useful feature works just like a car lighter .
This and the good lights are the reason i always chose the ttr on dark winter night .

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As funny as that was it was all kinds of wrong lol.

For one, you can fit a cigarette lighter if it's needed that much and (2). It will wear out things a lot quicker due to the extra heat and in extreme cases, burn a hole in the piston.

Jarrah  

 

Hp wrote:

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Not normal dude and may result in some expensive damage, have a little spray with some carb cleaner or wd40 around all the carb fittings and seals to make sure your not sucking in air. If the revs pick up as you are spraying then you know its sucking air. Also check if the air filter is seating correctly.
Easy things first :)

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 I am afraid that will not work. As 2wheelWillis  has suggested, it runs fine. If it was sucking air it would have a flat spot, especially on higher revs.

Checking that the air filter seating properly may be worth it, but unlikely that it would not be correctly fitted.

Jarrah

Hi, 2WheelWillis.

Since yours is a North American bike, I will risk telling you that mine (also North American) does the same--even when the air flow is choked off to the point that it will hardly run at all I can still see it glowing. Right now, it runs great at sea level, but the pipe does glow red in real dark conditions. I am reasonably sure that it is not running too lean, because it changes from running great at sea level to stumbling with signs of running too rich at between 4,000 and 5,000 ft. My carb is clean and jets, air box, and exhaust system are standard for North American bikes. It has been assessed and tuned by two different professional mechanics with many decades of experience, each.

I don't want to reopen the whole controversy, again, and I don't have any business directing you what to do, but I thought that you should know about my personal experience with this issue.

petenz wrote:

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I have not looked... but dose the TTR have a AIS. ?..

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 No!

Popping or backfiring is usually due to a lean or rich condition. In this case I highly doubt it is a rich condition. It can also be caused by the valves not seating correctly or misaligned timing.

Jarrah

Today for the first time i took the ttr for an offroadtrip, BIG FUN!!

Tonight i cleaned the bike with the high pressure hose and afterwards i started up the bike and let it run for a few minutes ,choke on and idle speed.

After a few minutes the headerpipe turned RED , don't think that's normal .

What could be the reason?

Just because he was running on choke?

was you engine hot if so it will struggle on choke you may have a mixture problem

Engine was cold when i started it, putted choke on and started ,ran for a max5'.
The headerpipe was very hot.
Only thing i changed was getting the intakesnorkel out.
Mixture problem ? to lean or to rich?

Some pics from the carb.

That plastic white tube ,is that necesary ?

What jets you guys run with the same set up , snorkel and headerpipe restriction gone.?

 

the snorkel would not affect this problem i cannot see pics clearly ask ttr fan for std jets & air screw is air filter clean not using oil etc

more common than you think.... my XT660 dose it...
My TTR prob dose aswell not let it idle long enough in low light

to see it.....

no air flow over the pipe to cool it...

if the plugs not white.. prob no issue...

the easy fix is not to leave it idleing to long...






.......

-- Edited by petenz on Friday 16th of December 2016 06:22:01 AM

petenz wrote:

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more common than you think.... my XT660 dose it...
My TTR prob dose aswell not let it idle long enough in low light

to see it.....

no air flow over the pipe to cool it...

if the plugs not white.. prob no issue...

the easy fix is not to leave it idleing to long...

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Agree 100% it's thin stainless steel with no airflow very easy to get glowing 

I've had blisters from the gearbox burning me trough the boots mustering cattle it's amazing how hot they can get 


.......

Come back Jarrah

We need people to debate different ideas.

Never tried to see if mine does it in the dark, will have a look sometime, so this may be a normal phenomenon !

Running lean would not make a difference to the temperature? Why have we seen pistons that have been running lean with heat damage and in extreme cases I have heard of holes in the piston, just would like to know and put it in my new carb journal 

As I am still learning about this stuff and some answers may help others.

TTRfan wrote:

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Why would a lean mixture cause the exhaust gases to be any hotter than a correct or rich mixture? I would have thought the the more efficient the burn in the combustion chamber the hotter the exhaust gases would be?

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 Very easy answer on why lean mixture causes more heat 

A lean mixture burns slower so it's still burning when it's pushed into the exhaust .a rich mixture is incomplete pushing unburnt fuel through slightly cooling temps .

First thing I learnt back doing my engine tuning training back in the day  

So as suggested watching average fuel consumption is prob the best on the ttr as it's not a highly stressed engine and is usually slightly rich from standard as air cooled engines like a little extra cooling 

Water cooled bikes are a bit more forgiving 

welp long story but bought a 06 ttr250 lil while back, here in Kentucky, usa, and carb was in a coffee can. So a few forth and backs of ordering parts and assembling, i completed the carb and installed it. She started up with choke, and ran off choke but very high idle. I may have to back off the throttle slide, stop screw. It was just dark when i got bike running and after a minute of high idle the header pipe was glowing red, so i shut it down and cleaned up tools. When i noticed red hot pipe i tried enriching the star shaped low circuit idle screw, to no noticeable difference in sound or heat.

Can yee all explain how i might be lean, i was meticulous doing the carb over, complete with checking every orifice after a good ultasonic cleaning. Did many a carb before so please rule out the obvious. Also no air leaks at boots, etc. everything is stock, airbox, exhaust, so are the jets. 

I appreciate any and all experience and knowledge shared on a lean condition and solution. Thanks

thats why i ad methonol to the gas and jet u pilot jet up a click and richen the needle its runing to lean clean the carby and she will run mint