TTR 250 Mods/Links/Pics....

This thread contains pictures/links and other miscellaneous things in which you can do to “un-cork” the power of your TTR-250. My goal is that this thread/sticky will be a guide as well as an aid for any questions you have.

You take full responsibility for anything you do to your bike... :thumbsup:

First Download the TTR 250 service manual HERE (This will be your best friend as it will come in handy and it’s free.)

Air Box Mod:

This mod simply consists of removing the snorkel. If you want you can cut a 2.5 X 3 in square in the top of the air box to draw more air in. Once you have opened up the air box, you should buy a high flow after market air filter. Uni air filters work good and they can be bought from the Thumper Talk Store HERE

Exhaust Mod:

The stock exhaust pipe is rather restrictive and quite which doesn’t yield the full power out put. You can fix this one of two ways.

1) First is to modify the stock exhaust. If money is an issue or your good with hacking stuff up then is might just be your best bet. If you have a non-USA model you need to remove the restructure in the header… HERE. For further details and pictures please see THIS write up at

2) Second is to purchase an after market exhaust. When it comes to after market exhaust pipes, there are a few different ones out there that fit the TTR 250, I went with a Pro Circuit T-4 because I felt it was built the best compared to other exhausts. You can purchase this pipe up from the Thumper Talk Store HERE.

Please Note: After market exhausts and modified stock exhaust pipes are louder than stock. You can hear sound clips of different set ups HERE. I ride in California Nation forests with it and have not had any problems so....its not that bad :thumbsup:

So now you have 1) opened up the air box and 2) modified the exhaust in some way. Since you have done this, you need/must rejet your carburetor or else your bike will run lean. Running lean will significantly hurt the life of your engine. Don’t worry all the hard work has been done for you!

When it came time to rejet I had a hard time finding which jets to buy, what sizes to buy and where to buy them. The carb Yamaha uses on the TTR-250 is not a name brand carb. However, with that being said the carb on this bike does take Mikuni Jets.

Carb Removal:

To get the Carb out of the bike I used the service manual as a guide (CH 5)

-Take seat off bike

-Take gas tank off bike

-Take side plastics off

Once the Carb is out you need to remove the three screws on the bottom found HERE. Once you have removed the three screws, remove the bowl and turn the carb upside down. It should look like THIS (Sorry they are blurry)

Also while the carb is out, remove the throttle screw that restricts the throttle from only opening half way. By doing this, you will be able to open the throttle wide open and reach full speed!

Pilot Jet:

The top jet is called a pilot jet. This controls the first ¼ of the throttle. The stock pilot jet size is a 50; replace it with a 52.5 pilot jet. NOTE: Use a Mikuni pilot jet with part number VM28/486. You can order this pilot jet here. Also note that from time to time links break and no longer work. If for what ever reason the link to this jet no longer works, make a phone call. Western Power Sports sells this jet and many dealers sell Western Power Sport products.

Main Jet:

The middle jet in the picture is called the main jet. This jet controls the ¾ and up throttle. The stock main jet is 137, replace it with a 140 small round main jet. NOTE: You must run a small round main jet as the hex main jets hit the bottom of the bowl. The part number is Mikuni No. N102/221. You can order this pilot jet from the Thumper Talk Store HERE.

Once the jets are in put it all back together, take your time it’s not a race. Make sure to let the bowl fill up with gas before you start it. Once you do that twist the throttle twice and try to start it, my fired right up with out the choke!

Let the bike run a bit and then adjust the FUEL SCREW. Once you have done that your bike is now uncorked....happy riding.

Miscellaneous Parts and Accessories

Skid plate from Baja Designs just type ttr250 in the search box and you will see it.

MX Style rear fender from

Maier USA

Lowering Kit from

I would like to take a minute and say thank you to the people in this guys are great. Also if I have missed anything or think I should add something please let me know!

Other Helpful Sites

-Yamaha TTR250 FAQ Owned and operated by Brain Sussex

-OEM Parts


-Thumper Racing 325 Big Bore Review By: Bryan Wedmore


nice job :thumbsup:

That was beautiful :thumbsup:

Seriously this should be a sticky. There is alot of great information here. The only thing you need now are some handguards

Sticky Updated

Thanks again......very good post :thumbsup: some pictures

Excellent post. Found the last piece to Dual Sport my bike from the Baja Designs link you posted. The license plate bracket I've been looking for was on the TTR250 search.

Thanks again.

thats dad just added the pro circuit t-4, rejeted, airbox mod today...i post some new pictures later

Updated this post with some more links for parts. If you there is anything i missed let me know and ill add it. lets build this post to be the 250 sticky

Dear Mods,

Please make this a sticky....NOW

Small Round Main Jet (Mikuni No. N102/221)

the first link you posted...ill update the link in the first post i didnt realize it wasnt working

This is a great post. Why is this not a sticky yet?

The pics are great. I pulled the airbox out like in the pictures, makes getting to the carb alot easier. My question is:

Is there an easy way to disconnect the throttle cables from the carb for easy removal without messing up the free play and adjustments? I need to clean the carb. Was curious as to how you did it.


Is there an easy way to disconnect the throttle cables from the carb for easy removal without messing up the free play and adjustments? I need to clean the carb. Thanks.

just unscrew the cables, i was scared at first on taking them apart and messing with the free play but after playing with it for a few mins while i was putting it back together i seemed to figure out how it works. you cant really mess this up. i would take a picture of it before you take it off that way you have a visual on how it should look when you put it back together! hope this help if you have any other questions just ask


You didn't replace the needle jet, but did you change the clip setting at all or was it okay with stock setting?

You didn't replace the needle jet, but did you change the clip setting at all or was it okay with stock setting?

I didn't change the needle, it is perfect in the stock position. At first I thought that this bike wasn't sensitive to needle adjustments but now I think Yamaha put a needle with just the right taper in it for this application. Everyone I've talked to thats jetted this bike for a pipe/other mods says they didn't even touch the needle.

Well, I changed my needle last year. I dropped the clip one notch toward the tip to enrich the mid throttle a little. I don't know that it was necesseary but it does run excellent. I've never had any hesitation on the throttle. I can go from any position to full throttle and it just goes there immediately. Who knows, maybe I'll switch it back to stock and see if there's any difference.

Did you need a special tool to remove the jets from the carb?

Did you need a special tool to remove the jets from the carb?

A small flat head screw driver for the pilot jet and a the right size socket (6mm I think) for the main jet

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