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

Terrence R · Senior Member

Throttle stop, myth or fact?

TT-R250M · Super Guru

The TTR250 is brought out from the factory with the throttle stop adjusted so you cannot use full throttle. It only goes to just before full throttle. So, yes you will be able to get a bit more by adjusting it until full throttle is reached.

To do this you must remove the carb and carb top cover to check that when full throttle is reached, the throttle stop ''stops'' it. Failure to make sure that the throttle stop is doing it's job and is not overextending the carb slide could cause damage to it or the top of the carb.

Jarrah

TTRfan · Super Guru

This is the "official" take on it from the manual:

Carb stop adjustment.jpg

ttboof · Super Guru

spot on.brian smile

TT-R250M · Super Guru

TTRfan wrote:
This is the "official" take on it from the manual:

Keep in mind that that is most probably the standard Yamaha setting. To reach full throttle I would think it would be better to use the method that I mentioned above.

Jarrah

saintken · Veteran Member

According to the diagram Brian posted the throttle slide is already clear of the venturi so you already have the maximum "opening" possible, if you raise the the slide further you will only enrichen the mixture due to the taper on the needle. In fact if you raise the slide more you will create a pocket at the top of the venturi which may create turbulance and not help the induction process.

Cubber · Super Guru

I agree with Brian & Saintken, sorry Jarrah. hmm

Who, in all honesty, really opens their throttle fully, anyway? confuse

And if they do, for how long when compared with the rest of their riding? confuse confuse

For my money if I wanted more power than my TTR has then I'd get a bike that gives me more power (I have that bike too - so I don't want another). smile

Martyn

TT-R250M · Super Guru

Cubber wrote:
I agree with Brian & Saintken, sorry Jarrah.
Who, in all honesty, really opens their throttle fully, anyway?
And if they do, for how long when compared with the rest of their riding?
For my money if I wanted more power than my TTR has then I'd get a bike that gives me more power (I have that bike too - so I don't want another).
Martyn

You are all welcome to your opinion, I stand firm on mine.

Jarrah

Terrence R · Senior Member

Can I visually inspect and adjust the throttle stop with the carb on the bike, the air box completely removed, and twisting the throttle to verify the proper slide height?

ttboof · Super Guru

Terrence R wrote:
Can I visually inspect and adjust the throttle stop with the carb on the bike, the air box completely removed, and twisting the throttle to verify the proper slide height?

yes , its just a matter of being able to see the slide travel up to and just past the bore of the carby

saves disturbing the manifold rubber and cables as well as saving a bit of time (no use being slack unless your good at it )

-- Edited by ttboof on Sunday 16th of February 2014 04:17:10 AM

brindabella · Senior Member

this just HAS to be a myth.
a millimeter of extra throttle slide movement would surely not effect typical drive-by noise tests anyway, so is pointless for the factory.

my ttr was bought new and I asked for it to be in the shipping crate, out of curiosity.
so I had to assemble it and I can say how it was set up "from the factory".

one of the first things after initial assembly and test ride was to change the needle position.
so this meant I had a good look at where the stop was set, and it was perfect!

However, in the past I have bought a new 1996 Honda XR250, which ran absolutely horribly and would barely exceed 60kph on the first drive home from the bike shop. It was ridiculously restricted - with a screw which only allowed about half throttle and a thin metal plate almost completely blocking the inlet - imagine an airbox snorkel with the flow of drinking straw! It also had a main jet about HALF the proper size (luckily they came with an extra "racing" jet which was merely the proper standard jet). Other two stroke dirt bikes crudely set up to pass Australian Design Rules in the past have had a plate at the front of the exhaust header, right next to the port, which had a hole you could barely fit a pencil in, to restrict the bike.

It is examples like that which lie at the heart of the myth, bringing out our paranoia and raising our hopes of easily found power, but I don't reckon the ttr is "restricted" except maybe by the ridiculous 14/44 stock gearing, and arguably by the slight restriction in the header (though mine goes fine with the exhaust system completely intact). But I don't want to start an argument on that, just saying you would have to be very lucky to gain anything by a throttle cable adjustment on a new bike - but always useful to check it, of course.