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

Rger8 · Member

Adding pipe without Jetting & Airbox?

TT-R250M · Super Guru

I would advise to at least drop the needle clip position down as doing that will make it run lean. Especially if the air filter or airbox is upgraded.

Jarrah

petenz · Super Guru

I put the GYTR pipe & short header pipe on... Made it run like %#@$
Then cut the top out of the air box & put a OB filter in..
It's now running not to bad.. again confuse
still needs a little fidding to get it dead right..

-- Edited by petenz on Wednesday 18th of September 2013 06:18:05 AM

-- Edited by petenz on Wednesday 18th of September 2013 06:18:21 AM

Rger8 · Member

Jarrah,

So your saying it might run rich if I just throw the pipe on without mods? Wont the bike run hotter if it's to lean?

PS - I do have a GYT-R air filter on it .

Thanks for your feedback!

TT-R250M · Super Guru

Rger8 wrote:

Jarrah,

So your saying it might run rich if I just throw the pipe on without mods? Wont the bike run hotter if it's to lean?

No, I wrote that it would lean out the mixture...

TT-R250M wrote:
I would advise to at least drop the needle clip position down as doing that will make it run lean. Especially if the air filter or airbox is upgraded.
Jarrah

I suggested that you (at the very least) lower the needle circlip position which would make it a little richer.

Jarrah

TT-R250M · Super Guru

petenz wrote:
I put the GYTR pipe & short header pipe on... Made it run like %#@$
Then cut the top out of the air box & put a OB filter in..
It's now running not to bad.. again
still needs a little fidding to get it dead right..

-- Edited by petenz on Wednesday 18th of September 2013 06:18:05 AM

-- Edited by petenz on Wednesday 18th of September 2013 06:18:21 AM

The GYT-R is a different exhaust but when you upgrade the airflow on any bike you need the air filter to allow more airflow. It does not work half doing the job and all components should be upgraded at the same time.

When I had finished my mod's (see signature below) I ended up having to go up 3 sizes larger main jet and 2.5 increase on the pilot jet. The 6 Sigma jets are made with the same flow rate as YAMAHA.

Jarrah

TT-R250M · Super Guru

I thought I had better explain this properly...

If you upgrade the airflow on the exhaust port, you now have to upgrade the flow to the intake port. This is achieved by fitting a high flow air filter. For example, if you upgrade the exhaust without upgrading the air filter, you will run rich. This is because it wants to suck more air but can't, so it sucks more fuel instead.

The TTR250 has very restrictive air flow, especially the ports (they need porting and polishing), and the airbox needs upgrading also for maximum benefit.

You may not need to change the carb set up until you upgrade the airbox, but it would be good to at least check by dropping the needle clip position as mentioned in my previous post. Especially if planning on upgrading the airbox.

Jarrah

Rger8 · Member

Jarrah,

Thanks for the explanation on airflow. Gives me a better idea of what I need to do.

PS- Do you know what redline is on the TTR250? I have a 2003 blue U.S. Enduro version.

Thanks, Roger

TT-R250M · Super Guru

Rger8 wrote:
Jarrah,

Thanks for the explanation on airflow. Gives me a better idea of what I need to do.

PS- Do you know what redline is on the TTR250? I have a 2003 blue U.S. Enduro version.

Thanks, Roger

No problems Roger, glad to help

As for the redline- The 2001 Yamaha TT-R250 came with a 28-horsepower, 249 cc, four-stroke, single-cylinder, air-cooled, four-valves-per-cylinder, double overhead camshaft engine with a bore and stroke of 73 mm x 59.6 mm and a compression ratio of 10.3:1. It reached its maximum 28 horsepower at 8,500 rpm and had a maximum torque of 15 ft.-lbs. at 7,000 rpm.

Enjoy!

Jarrah

yamaha42 · Senior Member

15 ft.-lbs.? sounds a bit low!

TT-R250M · Super Guru

yamaha42 wrote:
15 ft.-lbs.? sounds a bit low!

I don't get payed enough round here to make you believe it. biggrin biggrin

If you want higher than 15 ft.-lbs, buy a WR400. wink

Jarrah

petenz · Super Guru

28hp will be crank HP... they are around 21HP at the rear wheel..
which works out about right as on avarage a bike motor loses
around 20% from mechanical drag etc between crank & rear wheel..

I have to weld a 1/4bsp fitting in the header pipe as I have a air/fuel ratio
gauge I use the set the XT660R injection..great as it takes the guess work
out of getting it right... wonder what the optimin A/F ratio for the TTR is ?
The XTR I set for 13.6/1 for a constant throttle setting & jumps to 14.1/1
when the throttle is opened... Is what a pumper carb trys to do..

Bugeye_bob · Veteran Member

stoich for normal fuel is around 14.7

TTRfan · Super Guru

petenz wrote:
I have to weld a 1/4bsp fitting in the header pipe as I have a air/fuel ratio
gauge I use the set the XT660R injection..great as it takes the guess work
out of getting it right....

Hi Pete

Sounds interesting. How does that work then?

Brian

petenz · Super Guru

TTRfan wrote:
petenz wrote:
I have to weld a 1/4bsp fitting in the header pipe as I have a air/fuel ratio
gauge I use the set the XT660R injection..great as it takes the guess work
out of getting it right....
Hi Pete
Sounds interesting. How does that work then?
Brian

They are very simple...

hook them to the battery... put the sensor in the exhaust header pipe...

you need it in before any joins in the pipe.. If you have a leak air getting

sucked in.. It will screw up the reading..

There are a lot cheaper ones... mine was $60NZ

http://www.ebay.com/itm/INNOVATE-3796-DB-DIGITAL-AIR-FUEL-RATIO-GAUGE-WITH-LC-1-/370521765969?pt=Motors_Car_Truck_Parts_Accessories&hash=item5644d17851&vxp=mtr

brindabella · Senior Member

pete nz, that sure beats trying to read a spark plug (almost an extinct/useless art, with clean burning fuel and zappy ignition) !

you could just about make a rough 2D map of AFR on your TTR, using the sensor.
i.e. AFR at various combinations of throttle opening and rpm. (yeah, easier said than done).

if you did that, maybe you would hope to see (in an ideal world), that at high rpm wide open throttle you read about 13.0,
and at various medium throttle medium rpm scenarios, somewhere up towards stoichiometric value of 14.7.
and at idle who cares but maybe quite rich (eg 12.0) so it will idle ok when cool.

it should be momentarily richer at the instant the throttle was opened (due to the squirt from the "pump")
but that would be too quick for the meter to register.

if by a miracle the readings were optimal across the map you could mainly thank the designers of the emulsion tube.

it would be interesting to see the effect of jet or needle clip changes - they would distort the map, hopefully for the better.
but sadly with a simple(ish) carb, nothing will be perfect all over the map - swings and roundabouts.

BUT, unlike injection driven by sensors, our TTR250 carb cannot protect against going too lean,
eg if you tuned for riding at a high altitude in summer,
you would be running too lean at sea level in winter (where the oxygen density is higher).
so maybe you have to compromise to be safe.

I'd love to know what results you get, as would many others, I am sure. please keep us posted.

TTRfan · Super Guru

Air/fuel sensor

petenz · Super Guru

RE: Adding pipe without Jetting & Airbox?