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

noeyedear · Senior Member

cylinder head mods ??

TT-R250M · Super Guru

By cylinder head mods you mean port & polish right?

I have done this to my TTR250 and could not be happier with the results. The intake usually has quite a bit of porting to do, but the exhaust should not take as long. What you want to do is take out the casting imperfections & port it a little to increase flow. To do this, port where it curves around to the valve. If you do not do it right it will not be a performance increase, more like wasting fuel for nothing.

I started off using an old dentist drill, but it started playing up, so I had the rest finished by my local mechanic for $30.00.

All in all- highly reccomended

Jarrah

noeyedear · Senior Member

thanks for fast response. so basically you smooth the inlet, just on the valve side bend ??and make the inside mirror like and enlarge the exhaust side a little. any pictures ? might have to go on the todo list.

TTRfan · Super Guru

There is a school of thought that a mirror finish is not good as some turbulence from the port walls helps mix the fuel and air.

It is worthwhile checking if the carb stub sits tidily on the head. If any of the head protrudes into the inlet tract then it is worth marking it and filing it back as that createstoo much turbulence.

I have a head on the bench which was allegedly ported but I am struggling to see the difference. Also, the bolt holes on the cam gears have been elongated allowing the cam timing to be advanced. Without trying it back to back with standard cams I have no way of knowing if that gave a power improvement.

As I understand it, you need to do the full range of mods to get maximum benefit i.e. intake, valves, cam and ignition timing, raise compression, exhaust, etc.

But at the end of the day there is no substitute for cubes IMHO wink

Brian

Lostboyscout · Veteran Member

I'll go with Brian on this there ain't no substitute for cubic inches ......
And I've seen you with a grinder ......lol

TT-R250M · Super Guru

The intake port of the TTR250 is rough cut and also has a lot of imperfections. Porting will definately help for performance but as Brian suggested, you would need to upgrade further (re-jet) to get the full benifiet from this.

The intake should not be polished to the extreme as it will make the fuel puddle rather than atomize. The exhaust on the other hand can and should be polished for better air flow.

Here are some pics from when I did this..

First the intake side...

Now the exhaust side ported & slightly polished. May finish off the polishing if i have time...

noeyedear · Senior Member

Ok, I am going to give it ago. Easy on the inlet side leaving slightly rough, and polishing exhaust side. Someone mentioned valves, can I fit larger/better ?the exhaust is sorted, so reject carb, and thinking as I might need a rebore might go for. Third oversize, 260cc ?? What you all think???????

TTRfan · Super Guru

If you are going for a big rebore you might as well go the whole hog and the 2.0mm oversize. The TTR engine is reliable so the engine should last.

Another barrel or re-sleeve wouldn't be that expensive if the worst happened! The after-market pistons, such as Wossner and Wiseco, usually promise a higher CR as well which is another bonus.

Brian

noeyedear · Senior Member

2mm oversize, , porting and polishing the head, and motad exhaust, with shorty header, reject the carb, anything I am missing??

TTRfan · Super Guru

Clip ons and rear sets biggrin biggrin biggrin biggrin

mud · Veteran Member

Mod the airbox with a bigger hole, or trim the snorkel, a better filter and check your throttle stop. My throttle stop was set at half way, probably from the factory which I found amazing for a 1993 bike! 2 minutes with a spanner and she certainly woke up!

Cheers Mud

Lostboyscout · Veteran Member

noeyedear wrote:
2mm oversize, , porting and polishing the head, and motad exhaust, with shorty header, reject the carb, anything I am missing??

I want to know what you gana use if you 'reject' the carb ?

Are you going fuel injection ?

Could go blower too !

Lol!

TT-R250M · Super Guru

Fuel injection is not an upgrade for performance, rather an upgrade for less maintenance and better mpg than a carb. By no means will injection beat a carb for performance, unless it is direct injection.

Jarrah

texasT · Senior Member

Lostboyscout wrote:
noeyedear wrote:
2mm oversize, , porting and polishing the head, and motad exhaust, with shorty header, reject the carb, anything I am missing??
I want to know what you gana use if you 'reject' the carb ?
Are you going fuel injection ?
Could go blower too !
Lol!

I hope noeyedear really meant "re-jet" not 'reject'. blankstare ...Or maybe I ain't getting the joke, and you lost THIS ol' scout! confuse

BTW-Careful about that blower comment Lostboyscout, next thing Jarrah may try to do is go that route, just to see how much more power he can get

greg

TT-R250M · Super Guru

texasT wrote:
Lostboyscout wrote:
noeyedear wrote:
2mm oversize, , porting and polishing the head, and motad exhaust, with shorty header, reject the carb, anything I am missing??
I want to know what you gana use if you 'reject' the carb ?
Are you going fuel injection ?
Could go blower too !
Lol!
I hope noeyedear really meant "re-jet" not 'reject'. ...Or maybe I ain't getting the joke, and you lost THIS ol' scout!
BTW-Careful about that blower comment Lostboyscout, next thing Jarrah may try to do is go that route, just to see how much more power he can get
greg

LOL Greg

I already have HEAPS of power (for a TTR250) and if I want more I can always take my WR400 for a spin- well when I get it rebuilt lol smile

Thinking- should put the blower on my WR400 instead? Hmm... maybe not lol smile

Jarrah

mingle · Veteran Member

Do the 7mm overbore. Aka 325 kit. Along with porting. No replacement for displacement.

TT-R250M · Super Guru

mingle wrote:
Do the 7mm overbore. Aka 325 kit. Along with porting. No replacement for displacement.

There is also no liability with two mm over-size reliability wink

Just my 2 cents lol smile

Jarrah

Lin · Senior Member

TT-R250M wrote:

Fuel injection is not an upgrade for performance, rather an upgrade for less maintenance and better mpg than a carb. By no means will injection beat a carb for performance, unless it is direct injection.
Jarrah

Interesting. Jarrah can you enlarge on why a carb would offer better performance than port fuel injection?

TT-R250M · Super Guru

Lin wrote:
TT-R250M wrote:

Fuel injection is not an upgrade for performance, rather an upgrade for less maintenance and better mpg than a carb. By no means will injection beat a carb for performance, unless it is direct injection.
Jarrah
Interesting. Jarrah can you enlarge on why a carb would offer better performance than port fuel injection?

Once you have a bike jetted PROPERLY there is not much else you can do to make it go faster. On a TTR250 this would be a waste of time unless you wanted to get slightly more response and smooth delivery. The engine is not HUGE so it can only push so much air/fuel through at one time. Trying to feed it more fuel/air than it can burn and exhaust will not work no matter how hard you try. Also, relying on an ECU to deliver the right amount can be hit and miss. Unless the ECU is upgraded along with the fuel maps it is not all that great anyway. The ports of a TTR are not designed for fuel injection so this would be a factor to take into consideration also. While fuel injection would have some benefit it would not be much of an upgrade given that the carb is dialled in.

The reason the injected is able to deliver a smoother response from idle is the fact that it does not have to wait until the engine sucks air from the air filter to the engine and therefore supplying fuel. The TTR250 has an accelerator pump that squirts fuel in to stop the ''lean off idle'' problem that older carbs have and gives quite good throttle response already. Without direct injection this is not much of a benefit unless your talking throttle response. The atomization is not much different to modern carburettors so there is not much to compare with that apart from fuel efficiency and smoother delivery (obviously fuel injected being more efficient and smoother).

From experience- I have ridden with a fuel injected YZ450, YZ450 non fuel injection and out of the three bikes the fuel injected was the slowest. I had to overtake him so I did not crash into him when starting off the mark (he had a headstart) lol. To add to this- another mate has the 04 YZ450 (naturally aspirated engine) and makes the fuel injected YZ450 look slow (even though they are both good riders). I know this paragraph is not proof of anything but says a bit.

This is not to take anything away from the ''believers'' of fuel injection. If you think that injecting your TTR is going to be better, by all means try it. I am just stating what I believe to be true.

petenz · Super Guru

TT-R250M wrote:

Lin wrote:
TT-R250M wrote:

Fuel injection is not an upgrade for performance, rather an upgrade for less maintenance and better mpg than a carb. By no means will injection beat a carb for performance, unless it is direct injection.
Jarrah
Interesting. Jarrah can you enlarge on why a carb would offer better performance than port fuel injection?
Once you have a bike jetted PROPERLY there is not much else you can do to make it go faster. On a TTR250 this would be a waste of time unless you wanted to get slightly more response and smooth delivery. The engine is not HUGE so it can only push so much air/fuel through at one time. Trying to feed it more fuel/air than it can burn and exhaust will not work no matter how hard you try. Also, relying on an ECU to deliver the right amount can be hit and miss. Unless the ECU is upgraded along with the fuel maps it is not all that great anyway. The ports of a TTR are not designed for fuel injection so this would be a factor to take into consideration also. While fuel injection would have some benefit it would not be much of an upgrade given that the carb is dialled in.
The reason the injected is able to deliver a smoother response from idle is the fact that it does not have to wait until the engine sucks air from the air filter to the engine and therefore supplying fuel. The TTR250 has an accelerator pump that squirts fuel in to stop the ''lean off idle'' problem that older carbs have and gives quite good throttle response already. Without direct injection this is not much of a benefit unless your talking throttle response. The atomization is not much different to modern carburettors so there is not much to compare with that apart from fuel efficiency and smoother delivery (obviously fuel injected being more efficient and smoother).

From experience- I have ridden with a fuel injected YZ450, YZ450 non fuel injection and out of the three bikes the fuel injected was the slowest. I had to overtake him so I did not crash into him when starting off the mark (he had a headstart) lol. To add to this- another mate has the 04 YZ450 (naturally aspirated engine) and makes the fuel injected YZ450 look slow (even though they are both good riders). I know this paragraph is not proof of anything but says a bit.
This is not to take anything away from the ''believers'' of fuel injection. If you think that injecting your TTR is going to be better, by all means try it. I am just stating what I believe to be true.

My XT660R which is injected...

what you say is some what true... but the injection has a few more little tricks up is sleeve..

ride at sea level / at 10,000 ft / thougth a desert / thought a rain forest... the injection will

alway hold the air , fuel at the same ratio by means of a air temp sencer in the air box & a O2

sencer in the exhuast pipe... open the throttle to accelerate & it richen the mixture..

The XTR's ECU has a open & closed circuits..open circuit fuels at 14.7:1 , closed at 13.6:1

cruseing is on the close circuit , open the throttle it switchs to the open circuit...

I have a unit conected to the airbox temp sencer that lets me change the fueling at the turn of a nob

bascly it makes the temp sencer tell lies to the ECU about the air temp... tell the ECU the air temp is hotter

than it is and the ECU will lean out the air/fuel ratio.. tell it, it's colder & the ECU will richen the mixture..

but the ECU has set air/fuel ratios that it will not go out side of... so theres no chance of running to lean or rich..

TT-R250M · Super Guru

Yeah, that is the long story. I was talking about performance not whether or not you are running rich or lean. As mentioned, the TTR250 has the AP so it helps to regulate the lean condition that carburetors without the AP have. Provided you are not riding over huge mountains or riding at different elevations/climates, there is no need to adjust the fuel mixture.

Jarrah