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

Thomas ttr250 Williams · Veteran Member

Just ordered a fmf q4 from the us .

barra8 · Guru

That would be up to you but i would go either #150mm main jet or #148mm main jet with #50mm pilot.

If rejetting it would be advisable to buy a new pin (needle) but not absolutely neccessary.

Jarrah.

-- Edited by barra8 on Wednesday 12th of September 2012 07:52:04 AM

TTRfan · Super Guru

I guess it depends on what main jet you currently have installed.

If it's already a 147 then you may be OK just raising the needle a notch or two and richening up the pilot by turning it out a few turns.

Brian

barra8 · Guru

It will either run lean or rich

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If it runs rich the spark plug will turn black

If it runs lean it will form white crust

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It will either splutter at high revs and feel like it's starving =too lean

Or splutter down low and feel like the choke is on= too rich

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If you are going to upgrade your jets do it one mm at a time (where applicable) and see how it goes.

My bet is that #158 main jet or #150 main jet will be perfect (depending on your bike)

#50 mm pilot should be fine but #52.5 pilot jet may be needed (depending on your bike)

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#157 main jet should work although maybe not as desired (depending on your bike)

Air box mods will be needed for maximum performance

Also an air filter upgrade

Remember:

Don't go over #150 main jet or #52.5 pilot jet unless doing serious mods
Start at #147 main jet and 50mm pilot jet and work your way up.

.............................

Jarrah.

-- Edited by barra8 on Tuesday 11th of September 2012 01:44:58 AM

Thomas ttr250 Williams · Veteran Member

How will I know if I need to re-jet when I fit my exhaust tommorow ? What sings will be showing for a re-jet ?

TTRfan · Super Guru

Check out this thread - http://ttr250.activeboard.com/t49951533/jetting-information/

MotoWard or Fowlers are good mail order firms.

Brian

Thomas ttr250 Williams · Veteran Member

Jarrah thanks for the reply . Iv fitted the fmf and done about 2 miles only on the bike . And it seams to be running better than before. Don't want to ride any further as don't want to damage the engine in any way . Where could I purchase the 150 main jet and the 52.5 pilot in the uk ? Thanks

Thomas ttr250 Williams · Veteran Member

Is there any chance I could have the link to the exact jets I need for my bike not very michanical minded so haven't got a clue on witch jets to get on motoward. Im going to go wit a 150 main jet and a 52.5 pilot jet .

domski1 · Senior Member

Don't go over #150 main jet or #52.5 pilot jet unless doing serious mods
Start at #147 main jet and 50mm pilot jet and work your way up.

MotoWard or Fowlers are good mail order firms.

Google motoward for there phone number and then give them a ring to order the jets, I have used them and there service is really good.

Thomas ttr250 Williams · Veteran Member

Mods Iv got on my bike is a k&n filter trimmed snorkel . Uncorked the exhaust and fmf silencer . Is that enuf mods just to put a 150 main and 52.5 pilot do you think . The bike already got a 147 and a 50 pilot ?

barra8 · Guru

Should be buddy,

# 148 main jet might be more the go though but it will depend on your bike i guess.

I'd say go for it,if it's too rich go #158 main jet and #52.5 pilot

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Jarrah.

Cubber · Super Guru

Try this chart

Martyn

barra8 · Guru

Thomas ttr250 Williams wrote:
Does any one have a photo on how your spark plug should look when it's running perfect ? . As Iv orderd the jets and would like to compare. Thanks . Also with the 147 main and 50 pilot the spark plug started to get the white crust you said about jarrah

Means it's running too lean! Not good for the engine Go up to #150 main jet & 52.5 pilot & try that out. I think you may find that combination perfect.

........................................................................................................

Jarrah.

-- Edited by barra8 on Tuesday 18th of September 2012 10:31:21 PM

Thomas ttr250 Williams · Veteran Member

Does any one have a photo on how your spark plug should look when it's running perfect ? . As Iv orderd the jets and would like to compare. Thanks . Also with the 147 main and 50 pilot the spark plug started to get the white crust you said about jarrah

Thomas ttr250 Williams · Veteran Member

I phoned motoward and they want to see my jets to see if they can match them up . But they don't do a 52.5 pilot jet . Is there a certain make to the jets for my carb so I don't have to send my jets off for them to match them up ? Thank

domski1 · Senior Member

Just out of Interest did you have to pay any import tax on the exhaust?

TTRfan · Super Guru

Thomas ttr250 Williams wrote:
I phoned motoward and they want to see my jets to see if they can match them up . But they don't do a 52.5 pilot jet . Is there a certain make to the jets for my carb so I don't have to send my jets off for them to match them up ? Thank
____________________________________________________________________________________________

If you have a standard TTR carb then all the jetting info and part numbers can be found here

barra8 · Guru

Thomas ttr250 Williams wrote:
I payed £52 for customes on the exhaust

Unlucky We don't pay anything in AU unless the value is over $1000.00 biggrin

Howd you go finding jets? Any luck?

I'd help but there has already been so much talk already & can't be too hard

If your stuck see here Jetting help or here Jetting 101 or Help! Pilot jet differences? or Rich or lean or

stuttery running at low revs Low rpm stuttering q4 exhaust jetting

or here's a funny one Main nozzle differences wonder if that carby has a trunk aswell (no offence to anyone :)

There was heaps more but yeah good luck.

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By the way, i'm not sure who messed this thread up by making there post too wide but it is soo annoying furious lol biggrin

Someone in this thread needs to see here Notice to newcomers click here

Jarrah.

-- Edited by barra8 on Tuesday 18th of September 2012 10:57:52 PM

Thomas ttr250 Williams · Veteran Member

I payed £52 for customes on the exhaust

barra8 · Guru

This may help.

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My turn to ask for help wink

I am rebuilding a carb and want to go down from a 52.5 to a 50 pilot jet. The replacement jet looked right but didn't fit as the small diameter section was a tad too wide confuse

I have a new genuine Yamaha 50 pilot jet in my spares box but it is much shorter. See pic below:

Pilot jets.jpg

The shorter jet fits fine but will it work the same?

Anyone know if the jets are interchangeable please?

The only part number I can find is for the short jet 43F-14342-25

Brian

Later....

Good news biggrin

I decided to try the carb with the "wrong" length pilot jet in and it runs absolutely fine - no problems at all at low revs. Started well and ticks over nicely when warm.

Brian

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Jetting information	Reply Quote Printer Friendly

That is a really useful post and I will make it a sticky! My own experience is that the TTR isn't as sensitive to jet size as other more highly tuned bikes and therefore it is likely that standard Yam jets can be used, especially bearing in mind that there is additional adjustment via the different clip positions on the needle. I have highlighted in blue all the jets that I have bought in the UK from Yamaha dealers. I have found that some of the jets are no longer available but can't immediately recall which ones Standard Yamaha TTR250 pilot jets: 43F-14342-24 #48 43F-14342-25 #50 43F-14342-26 #52 43F-14342-27 #54 in US parts lists they probably have an extra '00' suffix, eg 43F-14342-25-00 Here are some Yamaha MAIN jet part numbers: (I'm not so sure about all these, though - 288-14343 types are from XT350?) 4GY-14329-69 #137 standard US 4GY-14329-73 #145 [AKA 288-14343-73?] 4GY-14329-74 #147 standard AU 288-14329-71 #142 (Fowlers say no longer available - 11 July 2012) 288-14329-74 #148 [AKA 288-14343-74?] 288-14329-75 #150 [AKA 288-14343-75?] 288-14329-76 #152 [AKA 288-14343-76?] 288-14343-68 #135 288-14343-70 #140 288-14329-78-00 №156 If anyone else can add to or improve the list please do so Brian

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If the pilot fits in the carby & is the right thread try it

If it starts,idles, runs well & aint running lean then alls well

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Jarrah.

-- Edited by barra8 on Saturday 22nd of September 2012 12:00:34 PM

Thomas ttr250 Williams · Veteran Member

Hi all I orderd the jets . The 150 main come back and was great but the 52.5 pilot jet was nothing like the standerd jet . It was same shape as the 150 jet that screwed in . The part number was ( Mk441160-052.5 ) does any one know what the part number is for a 52.5 pilot jet thanks . I got the last part number from a link on the forum

barra8 · Guru

Hey Thomas,

Good to see people appreciated the time we spend helping people. Also good to see a finished result.

On the carby subject...

I would suggest you drop your pin one setting for more instant responce.

Check that your pin still has a cylindical cone shaped point to it-- not just round & sharp.

If it does'nt have the cylindical cone shaped point don't worry.. It will still work but not as well as if you bought a new one.

Steps to dropping the pin.

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Take the top of the carby

Undo the bolt that holds the throttle slide arm on-you will see this looking straight down at carby with the top cover removed.
Now undo the two small philips head screws (inside the slide) --you will see this looking straight down the slide of the carby with the top cover removed.
Now remove the pin
Remove the circlip from the pin --taking note of what setting it's on
Replace the circlip one setting up the pin
Now put the carby back together.

Remember: The cut out in the throttle slide goes towards the air filter
Note: When removing carby (if you are) it is easier to remove the inlet manifold rubber boot rather than try to squeeze it out. I have broken a carby boot trying to squeeze it out.

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If it's still not quite right move it one more setting as described above

If your still not sure what i mean let me know,

Jarrah.

-- Edited by barra8 on Wednesday 26th of September 2012 01:54:11 PM

TTRfan · Super Guru

Thomas ttr250 Williams wrote:
Dropped the clip 1 slot And now it's got a terrible splutter .I didn't try it with the clip in standerd position tho . When it's reving hi it's great but if I want to bring the revs down it starts the spluttering . And I also haven touched the mixture screw . . Thanks again jarrah you been a great help

Sounds like its running much too rich.

Try it with the airbox cover off for just a short trip and see if it runs better. If it does, then that points to an over-rich rich mixture.

Brian

Thomas ttr250 Williams · Veteran Member

Do I need to move the pin in the carb and what grove should it be on . Any info be great . Thanks every 1 for the info so far

barra8 · Guru

Once you have done what Brian mentioned

While idling the bike screw the mixture screw in until it changes revs

Then turn it out one and a half turns (roughly)

Now give it a rev and adjust it slightly while noticing where it runs best.

You will need to set it out about another 1/2 - a full turn from the standard setting.

Try that & if still bad you may need to go down to #148 Main but not likely.

Jarrah.

-- Edited by barra8 on Wednesday 26th of September 2012 09:38:44 PM

Thomas ttr250 Williams · Veteran Member

Dropped the clip 1 slot And now it's got a terrible splutter .I didn't try it with the clip in standerd position tho . When it's reving hi it's great but if I want to bring the revs down it starts the spluttering . And I also haven touched the mixture screw . . Thanks again jarrah you been a great help

Thomas ttr250 Williams · Veteran Member

I give it a run with the air box cover off and it was the best it's ever run . Really fast and responsive perfect . But air box cover on and it starts the spluttering again I also turned the mixture screw as you said and still the same I turned it everyway you could as I was ridding the bike to but no different . What would you recommend doing now ? Thanks

Thomas ttr250 Williams · Veteran Member

Also the mixture screw is the star shape screw under the carb as I couldn't find any other

TTRfan · Super Guru

Bit of a puzzle really as you said your engine was running weak on the standard jetting confuse

Are you sure that was the case?

Maybe go back to standard jetting, raise the needle and do a plug check after putting on a few miles?

Brian

barra8 · Guru

You will either have to go down to #148 main jet or back to #147mm. As Brian says it's a bit of a mystery as you said it was running lean with the standard jet? confuse

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Jarrah.

Thomas ttr250 Williams · Veteran Member

I've had this splutter since owning the bike only when hitting climb tho and the revs start dieing down the spluttering starts . And after the re-jet it's gone a lot worse . How comes when I take the air box cover off it runs perfect ? . Its like the bike needs more air intake

TTRfan · Super Guru

More air - or less petrol!

Presumably you have a good air filter that isn't over-oiled?

If your bike runs better with the cover off then it certainly points to a mixture problem and the assumption is that the spark plug and ignition circuit are OK.

Thomas ttr250 Williams · Veteran Member

Do I go down on the pilot jet if I go down to a 148 on main jet ?

TTRfan · Super Guru

Thomas ttr250 Williams wrote:
Do I go down on the pilot jet if I go down to a 148 on main jet ?

In my experience the pilot jet doesn't make much of a difference - unless it gets totally blocked that is! It is used in only a small part of the rev range. I wouldn't worry too much as you can adjust it on the turn screw anyways.

Brian