ttr-125 jetting question

39 replies to this topic
  • Thumpin2do

Posted July 04, 2007 - 06:58 PM


Hey all, this is my first post. I have a 2006 ttr 125. I installed a 17.5 pilot and a 110 main jet and removed the snorkel from the airbox. Now it wants to cut out at higher revs. Anybody know what I should do?

  • SX89

Posted July 04, 2007 - 07:07 PM


you are probabaly to rich on the main jet and needle.. try a smaller main

My buddies 01 was real lean stock but when we removed the snorkel it ran much better especially high RPMs and that was without jet changes

Try getting to high RPMs with as little throttle as possible (like 1/4 or 1/2)
If you can get there then you are too rich so if that happens try a bigger main,, if it gets worse than before try the 20 main

  • Thumpin2do

Posted July 04, 2007 - 07:19 PM


Thanks SX89. I'll keep trying.

  • ovrrdrive

Posted July 05, 2007 - 01:14 AM


I'm guessing you're too rich on the main too.

If you just pulled the snorkel out it's probably not getting enough air in it to warrant the 110 main. If you want to keep the 110 in there cut the top of the airbox some and do the washer mod to the exhaust and it will probably be fine.

If you don't want to mod it any further, you'll probably need to go back to either the stock main or possibly the 107.5. This time of year the bikes are rich anyway due to temp and humidity so it wouldn't surprise me if you needed the 105 if you don't have any other mods.

You'll be fine with the 17.5 pilot though as you can turn it back with the fuel screw.

  • Thumpin2do

Posted July 05, 2007 - 01:06 PM


Thanks ovvrdrive. I'm just trying to get more bang for not too many bucks. Ha Ha

  • Thumpin2do

Posted July 06, 2007 - 01:57 PM


O.K. I left the 110 main jet installed and cut five 7/8" holes in top
of the airbox beside the snorkel hole(arranged like five on dice),
removed the screen
from behind the air filter and put one washer(approx. 3/32" thick) on
exhaust tip bolt to shim out the exhaust tip. I noticed an improvement
at higher rpm's in that it no longer bogs transitioning from midrange
to top end
and it seems to cut out when you get it wide open.
Also at low rpm's (near idlle speed) when you snap the throttle quickly
it will
die. If you roll the throttle on more slowly it does better. Its like
there is a
little hesitation when you roll the throttle off and back on while
I have the 17.5 pilot jet and 110 main jet. It is hot and humid here in
Alabama. Any advice would be greatly appreciated.

  • ovrrdrive

Posted July 06, 2007 - 04:04 PM


Snapping the throttle on a bike without an accelerator pump is a good way to create a bog but you should still be able to open it up rather quickly. What's more important though is to figure out at what throttle positions you're having the problem.

From your description it sounds like you're still having problems at wide open throttle which is the main. The problem is that being lean or rich will both create a bog you just have to learn which is which. A rich bog is rather sudden and the bike feels like it's being choked out. Sometimes you'll get a puff of black smoke out the back too. A lean bog feels like the engine just sort of falls off and just starves for fuel. The motor will also run hotter when it's running lean.

It sounds like your airbox and exhaust are fine now. I'd probably try out a 112.5 jet and see what it does.

Btw, are you sure the carb is clean?

  • Thumpin2do

Posted July 06, 2007 - 07:01 PM


I have about 3hrs. on the bike. The air filter is still clean. The
carburator is
brand new and is not dirty.

The throttle position where I'm having the trouble is just off idle.
The bike is warmed up after 5 minutes of testing, transmission in
sitting on the side stand idling, try to twist the throttle sort of
quickly and
the bike just dies.

Is this an air screw issue?

Wouldn't a 112.5 be too rich for high heat and humidity?

In hindsight I kind of wish I had just put the 17.5 pilot jet in and
left the main
jet, airbox and exhaust tip alone. I was just wanting an easy way to
increase the engine performance a little bit. It comes on stronger(I
think) in the midrange but when you speed shift and try lift the front
wheel it kind of studders.

I have a 112.5 main jet I can try but I'm wondering why it dies when
opening the throttle quickly off idle.

This can be a little frustrating:confused:

  • ovrrdrive

Posted July 07, 2007 - 04:31 AM


How many turns out are you on the fuel screw?

Does it pop or backfire when you decelerate?

Hanging idle at all?

It can't hurt to try going out a little on the screw. This time of year I'm out to around 2.5-3 turns. Bogging at that throttle position would kind of indicate a pilot or fuel screw issue...

  • Thumpin2do

Posted July 07, 2007 - 05:05 AM


I have not adjusted the fuel screw yet.

I have noticed no popping or backfiring on decceleration.

The bike will idle fine. Please define hanging idle.

I was kind of thinking a pilot or fuel screw issue also because of the
throttle position.

I will record my stock fuel screw setting and try to clean the low end
up by adjusting it. If not I'm back to square one. I hope the 17.5 is

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  • Hawker

Posted July 07, 2007 - 05:32 AM


Raise the needle/lower the clip. Your off idle bog is a lean condition. Sometimes after the airbox mod they will completly die if you touch the throttle. I put the clip in the lowest position in the summer and then a small washer under it in the winter.

Hanging idle happens when you let off the throttle and come to a stop and the bike is idling high.

  • Thumpin2do

Posted July 07, 2007 - 07:30 AM


Thank you Hawker for your response. I have read that no one has
recommended changing the clip position on the jet needle but I am willing to
try. I see from the service manual(page 4-7) that there are three clip
positions and that the standard clip position in the number two groove.
I will try the number three groove which lowers the clip and raises the
needle. My
pilot air screw(#18 on page 4-4) is still at the factory setting. Is
this something I will have to adjust along with raising the needle?

At this time my bike is not hanging idle. Thanks for the definition.

I really appreciate everyones help!!!:thumbsup:

  • ovrrdrive

Posted July 07, 2007 - 02:05 PM


Most people leave the needle alone but there is definitely some tuning that can be done with it depending on the way the bike is running. 95% of all of these bikes don't need the needle messed with but I have seen some people swear by it.

Just remember how it's running now and if it doesn't get better put it back.

If you've never messed with the fuel screw there's a good chance that will help out though...

  • Thumpin2do

Posted July 07, 2007 - 03:20 PM


Thanks ovrrdrive, I'll try a few things one by one and keep ya'll
I'm kind of tempted to try the 20 pilot just to see what it will do.
Thanks for all the advice and ideas.:thumbsup:

  • Thumpin2do

Posted July 07, 2007 - 07:22 PM


O.K. Here is what I did. I pulled the throttle valve and removed the
jet needle.
I couldn't believe what I saw. The jet needle only had one groove for
the clip. I am not joking I am serious. The service manual shows three
grooves but apparantly Yamaha doesn't think it is necessary to adjust it
and is saving a few nickels on manufacturing costs. This is an 06. I
have not checked it on my 05. Also there was a plug covering the fuel
screw(aka pilot air screw[#18 on page 4-4]) which I had to remove in
order to adjust it which I know my 05 did not have from the factory.
Anyway, the factory setting was 1 1/2 turns out. I set it at 2 1/2 turns out
and then tested.

First of all the engine had not been run all day so it was cold. It
cranked on the third or fourth kick using no choke and giving it no
throttle. What's up with that? After letting it idle for about two minutes I
took it for a little test ride for about five minutes. It seems to run
pretty good through the midrange and top end and doesn't seem to fall
off so much when you over rev. It does still bog out or die right off of
idle when you twist the throttle quickly.

Correct me if I'm wrong. Idle to 1/4 throttle-pilot jet. 1/4 throttle
to 3/4 throttle-jet needle. 3/4 throttle to full throttle-main jet. All
three affected by fuel screw.

I'm tempted to try the #20 pilot jet next to see if it helps throttle
response near idle and then maybe the 112.5 main jet to see if it runs
better on top.

Summary of mods so far: Removed snorkel and screen from airbox. Drilled
five 7/8th inch holes in top of airbox. Washers installed to shim
exhaust tip. 17.5 pilot jet and 110 main jet installed. 2 1/2 turns out on
fuel screw.
250 feet above sea level. Hot and humid.

All thoughts and opinions are welcomed. Thanks!!!

  • Hawker

Posted July 08, 2007 - 01:42 AM


I have raised the needle on 7 different TTR's. All with good results. 2 of them were not rejetted just the needle raised and made a big improvment. You can fatten the jets up all you want but if the needle is too low it will be blocking all the gas. I have never really messed with the fuel screw except to make sure its 2.5 turns out.

The 2 stock TTR's I have I run 17.5 pilots, 107.5 mains, airbox mod, needle clip in the lowest postion. They both have aftermarket exhuast on them. They are both 03's.

If your needle only has 1 clip position look for a small washer at the hardware store. Something for a #4 machine screw might work.

Good luck

  • ovrrdrive

Posted July 08, 2007 - 04:23 AM


So everything is running great but you just still have the off idle bog right?

On the needles without grooves (yep it's common on certain years) people do just what was suggetsed above with the washer and it works great. If you don't want to do that you should be able to order the correct jet from Yamaha but I don't have the part number. The washer trick seems to work fine.

As for if it will correct your problem you'll just have to try it out and see. As you've already seen the fuel screw is pretty important in these carbs. I bet you could fiddle with it and work out most of your problems but it can't hurt to try other things as well. Just be sure to try them one at a time so you know what fixes it when you find it. By trying a combination of different jets, fuel screw positions and needle heights you'll eventually get it nailed.

Of course, it could be something else like float height too... It wouldn't hurt to check that. The procedure is in your manual but if you don't have it I've posted scans a few threads.

  • Thumpin2do

Posted July 09, 2007 - 05:45 PM


Yes, it runs pretty good except that it is a little flat on over rev and bogs at idle when you try to snap the throttle quickly. Maybe I should try 3 turns out on the fuel screw.

  • ovrrdrive

Posted July 10, 2007 - 01:03 AM


You should be fine at 3-3.5 turns out on the fuel screw but if you need to go further than that you should go to the 20 pilot. You could put it in now and go back in on the fuel screw and that should even it out too. It never hurts to try...

Other than that, if you're having your trouble at 3/4 throttle and above that's the main jet's territory. All indications are that you might be lean there. If you have the 112.5 I think I'd give it a try.

Remember, all of the information on these forums are just baselines. Every bike is different. Try the 112.5 main and if that makes it worse try the 107.5.

  • Thumpin2do

Posted July 10, 2007 - 03:38 AM


Thank you for your response ovrrdrive, your insight is very helpful. I
have found out that there are unused ponies hiding inside this little
engine. It was amazing how strong my bike has gotten in the midrange.
The front tire lifted almost effortlessly while attempting the speed
shift test into third gear, something that it would not do before. Although
tuning the carb has been a little frustrating I think I can see the
light at the end of the tunnel. These bikes are really fun! I plan on
doing some more experimenting this week. Thanks!!!


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