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

bbarfield · Veteran Member

Pipe, Jets and Airbox - Merry Christmas To Me

bbarfield · Veteran Member

I found this excellent psot on the other TTR website. Has anyone tried these exact jet sizes they mention? 52.5 and 140

http://www.thumpertalk.com/topic/282432-ttr-250-modslinkspics/

ERBS · Veteran Member

If your going to get an exhaust, Brian has an aftermarket exhaust that releases a few more ponies from the stable and still is just a quiet and lighter than the original, might invest in a zaust for my ttr from Brian as it's got to last a lifetime

TT-R250M · Super Guru

bbarfield wrote:
I found this excellent psot on the other TTR website. Has anyone tried these exact jet sizes they mention? 52.5 and 140
http://www.thumpertalk.com/topic/282432-ttr-250-modslinkspics/

A good rule of thumb is to upgrade the pilot and main jet 2~3 sizes.

If using a Mikuni jets, a 140 main would be equivalent to a #150 main. The Mikuni jets that fit are ''small round'', although I would recommend using the shorter main nozzle/emulsion tube from the earlier 1993~1999 model, as the Mikuni jets do not leave much space between the bottom of the float bowl and the bottom of the jet.

The price of the Powercore seems about right, can't say how good they are but they are loud!

I bought the 6 Sigma jet kit from eBay and am most pleased. You can buy the jets from JetsRus.com, eBay, or other online stores.

Jarrah

bbarfield · Veteran Member

Has anyone tried one of these DG brand exhaust pipes? This looks identical to the Brian exhaust mentioned above. But at $150, I hope it's not a "get what you pay for" type of bargain. I want to get the most power possible and spend under $250. If the Powercore is the best tool for that, I'll deal with the noise, or buy the $35 silencer insert when needed.

ERBS...can you comment on how the Brian style exhaust compares with the other brands?

http://www.amazon.com/DG-Performance-02-4250-R-Series-Burnished/dp/B00CJF47IU/ref=sr_1_2?s=automotive&ie=UTF8&qid=1384898009&sr=1-2&keywords=exhaust+for+TTR250

bbarfield · Veteran Member

I just tried to install my new jets and have problems with both of them. On the main jet, I ordered the small round jet, size 52.5. But the new one appears to have threads that are slightly smaller, or a different thread type. It feels like I can probably drive it on in there, but I obviously don't want to do any damage.

For the pilot jet, the threads are fine. But the new jet is way longer than the original, so it doesn't recess up into the housing like the original did.

I feel like I ordered the wrong parts, but I used the model numbers provided in the sticky.

Any insight on this? See picks below.

texasT · Senior Member

Hi Brandon,
Glad to see another TTR man in the U.S.A.!
My OEM jet (#50) looks like the short one you show (in middle/
I think you may have gotten the wrong part (Bottom row)?
When I rebuilt mine a while back, I ordered my jet from Bikebandit Part 43F-14342-25-00
I think forcing it any could damage carb so be careful! make sure everything is clean.
Greg

TT-R250M · Super Guru

bbarfield wrote:
I just tried to install my new jets and have problems with both of them. On the main jet, I ordered the small round jet, size 52.5.

TT-R250M wrote:

If using a Mikuni jets, a 140 main would be equivalent to a #150 main.
Jarrah

Not sure why but nobody listens to me when it comes to buying Mikuni jets!

Should I waste my time letting you know you have the right parts but wrong sizes?

Jarrah

bbarfield · Veteran Member

I did listen to you Jarrah. I bought the Mikuni Pilot Jet size 52.5 (VM28/486) and the Mikuni main jet size 140 (N102.221). These are the exact part numbers listed on the sticky.

bbarfield · Veteran Member

I ordered my parts form Jets R Us.com. I was a bit confused because they have one column for pilot jets labeled Genuine Mikuni Jets, then another column right next to that labeled OEM Equivalent Mikuni Jets. I honestly wasn't sure which column to choose from, but noticed 52.5 wasn't offered on the OEM side. It stopped at 50. I had two columns listed for the main jet as well.

Two long lists popped up after I did an advanced search just for my model of bike. Perhaps the pilot jet being longer isn't a big deal, and those threads are just a bit tight. When you bough new jets, did they look exactly like the the old ones?

bbarfield · Veteran Member

According to the Jets r us website, the original and OEM equivalent jets should be exactly the same. So I'm not sure what the problem is.

TT-R250M · Super Guru

bbarfield wrote:
I did listen to you Jarrah. I bought the Mikuni Pilot Jet size 52.5 (VM28/486) and the Mikuni main jet size 140 (N102.221). These are the exact part numbers listed on the sticky.

Once again- If using a Mikuni jets, a 140 main would be equivalent to a #150 main.

bbarfield wrote:
I'm not sure what the problem is.

The problem is- in theory, you now have a pilot jet that is ten sizes too large.

The pilot being larger is not a problem and the Mikuni jets are not the right thread pitch but ''SQUEEK'' in.

Jarrah

bbarfield · Veteran Member

Ok...I think I see my error now.....

For the main jet, I wanted to go from 137 to 140. So I meant to order a Mikuni 150, using your suggestions. Now that I re-read my receipt, I have purchased the Mikuni 140. So I need to send it back and get the 150.

Now my goal on the pilot was to go from a 50 to a 52.5. So I ordered a Mikuni 52.5. I didn't think there was a variance for the brand vs. size on the pilot. So I'm still confused as to why the Mikuni pilot jet looks completely different from the original pilot. Should I have adjusted the size on this one as well?

I was actually following these other guidelines from Thumpertalk (http://www.thumpertalk.com/topic/282432-ttr-250-modslinkspics/), which I pulled from the Uncork The TTR Article on this website (http://www.thumpertalk.com/topic/282432-ttr-250-modslinkspics/). This article seemed spot-on, so I followed the suggestions verbatim, and assumed the brand differences were already factored in.

I'm sorry if I misunderstood, and hate to ask you to repeat yourself, but please clearly explain what I should do to correct each of these jets.

Thanks!

TT-R250M · Super Guru

Pilot Jet

A Mikuni #42.5 or #43 pilot jet would be more suitable as Mikuni sizes are different than Teikei. In theory a #42.5 would be the same as a #52.5 Teikei pilot jet.

Main Jet

A Mikuni #140 is the equivalent of a #150 Teikei/Yamaha. If using a Mikuni #140 main it will be either perfect or slightly rich. You may need to raise the jet needle clip position to lean the mixture out some-

If a #52.5 pilot has been used in the US with no problem than it is worth a shot. However, I would expect it to be too large and cause it to accelerate slowly from idle~1/3 throttle (maybe even pop/backfire).

Hope that clears up the confusion?

Jarrah

bbarfield · Veteran Member

Ok...yeah, I was way confused. So I'll keep the main, squeak it in, then adjust the needle clip as needed.

Ill return the pilot and order a 42.5. Thanks for all your help!

TT-R250M · Super Guru

I'm glad you have the right idea now wink

No problems, glad to answer any questions that may arise.

When adjusting the jet needle clip position- if you have it correct- it will splutter slightly from 1/3~full throttle and may pop on deceleration from full throttle if the clip is moved 2~3 settings lower (towards the sharp end).

Let us know how you go.

Jarrah

yamaha42 · Senior Member

I use a mikuni 42.5 pilot and a 137.5 small round main. The main jet won't screw flush to the nozzle, so I just screw it till it seats a little bit past lightly. Maybe a washer can be used underneath it?

TT-R250M · Super Guru

yamaha42 wrote:
I use a mikuni 42.5 pilot and a 137.5 small round main. The main jet won't screw flush to the nozzle, so I just screw it till it seats a little bit past lightly. Maybe a washer can be used underneath it?

Sounds like you got the jetting fairly correct for your mods and country

I have heard reports of the Mikuni jets not sealing properly, thank you for verifying this. If you want to use a washer you can but make sure that it does not make the main jet protrude further than without the washer, this could cause problems. Otherwise I would suggest to just tighten it in and be done with it.

Jarrah

chrisstdt · Senior Member

Just read the link to thumpertalk ,do uk ttrs have a restrictor in the header pipe ?

TT-R250M · Super Guru

chrisstdt wrote:
Just read the link to thumpertalk ,do uk ttrs have a restrictor in the header pipe ?

My understanding is that UK models do have the restrictor (from other owners previous posts).

The best way to find out would be to take the exhaust off and check as the previous owner may or may not have removed it.

Jarrah

Yuraku · Veteran Member

TT-R250M wrote:

My understanding is that UK models do have the restrictor (from other owners previous posts).
The best way to find out would be to take the exhaust off and check as the previous owner may or may not have removed it.
Jarrah

How do you take the exhaust off? confuse

Yuraka

TT-R250M · Super Guru

Yuraku wrote:
TT-R250M wrote:

My understanding is that UK models do have the restrictor (from other owners previous posts).
The best way to find out would be to take the exhaust off and check as the previous owner may or may not have removed it.
Jarrah
How do you take the exhaust off?
Yuraka

Take the RH side guard off (to make it easier), loosen header pipe~exhaust clamp (part 12 below), remove the two retaining bolts from the muffler (part(s) 17), remove the muffler, remove the header pipe retaining nuts (part(s) 16) , remove the front engine mount (not necessary apparently but makes it easier for me) and remove the header pipe.

Diagram of Yamaha Motorcycle Parts 2000 TTR250 - TTR250MC EXHAUST Diagram

Jarrah

Yuraku · Veteran Member

Thanks a bunch.

Which is the restrictor?

Is it item No 11 in the diagram or is it further in the header? confuse

Also - which "front engine mount" - there's one on the head and one in front of the engine? Neither is in the way of the header though. confuse confuse

Yuraku

-- Edited by Yuraku on Wednesday 18th of December 2013 07:47:53 PM

Yuraku · Veteran Member

Thank you another bunch.

The other front mount I was wondering about is shown No 16 in the diagram - I wasn't thinking of the rear "head steady" mounting. disbelief biggrin

I'm going to have to look at mine now - or is it only on UK models that are restricted?

Yuraku

TT-R250M · Super Guru

Yuraku wrote:
Thanks a bunch.
Which is the restrictor?
Is it item No 11 in the diagram or is it further in the header?
Also - which "front engine mount" - there's one on the head and one in front of the engine? Neither is in the way of the header though.
Yuraku

The restrictor is in the end of the header pipe. It does not have a part number and cannot be bought separate.

This is what the restrictor looks like (hope Brian doesn't mind?)-

detail+of+restrictor.jpg

To remove it cut the last 10mm from the header and it will come off with it. More info here- http://www.ttr250.com/#exhaust

This is Markvan's picture of his header pipe that has had the restrictor removed, hope he doesn't mind?

The engine mount in question is the front upper engine mount (not the upper one at the rear of the engine). As mentioned, this doesn't need to be removed but it makes it easier for me to fit the header pipe. However, I think it is because I have the US header pipe (restrictor not fitted standard in the US). See part number 11 below-

Diagram of Yamaha Motorcycle Parts 1999 TTR250LC FRAME Diagram

Jarrah

bbarfield · Veteran Member

I'm ready to try out my new jets. Do I have to completely reinstall the airbox in order to crank it? Or can I just fire it up in the garage with no box and rev it up on the stand to see how it run and determine if I need to adjust the needle clip?

bbarfield · Veteran Member

I put it back together and ran it up and down my street. Seems fine, with no popping or idling issues. But I'm pegging it out quite easily and getting just a bit of gurgling at the top. I can't tell if it's just that small sprocket that I'm not quite used to yet, or if I have a jetting issue. Itd hard to tell on my short street. I'll report back after I've hit the trails.

saintken · Veteran Member

You, ll never really know until you try it under a proper load wth a warm engine, find a big hill :)

Cubber · Super Guru

Welcome, Saintken.

Do you know Saint Nicholas - he's rather busy this time of year?

Martyn

TT-R250M · Super Guru

If you continue to have trouble, I would suggest going larger on pilot jet. The Keihin #42.5 may not be large enough.

What are the symptoms and at what rev range etc.?

Jarrah