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

nwrider · Veteran Member

Carb - jetting information

TDVT · Senior Member

Jetting information

TTRfan · Super Guru

Carb - jetting information

brindabella · Senior Member

RE: jets long or short?

TTRfan · Super Guru

Hmmm - just had a call from Fowlers and the 142 jet is no longer available cry

The part numbers for the 140 and 145 are valid so I have ordered one of each but that doesn't mean they are still available. They are now on back order and I will let you know when I either get them or am told no longer available.

Brian

TDVT · Senior Member

brindabella wrote:
I don't get it - what is wrong with using standard jet alternatives for tuning?

If I had to guess, I would say availability of both parts & information. From what I had found, people were pretty pleased with the Mikuni substitutes so that started the ball rolling as more tried it, I guess. The Yamaha part numbers are also not as easy to find.

In my case, I was resurecting my bike from a long storage (previous owner's) & the carb was completely stopped up, so it seemed like good time to do the swap as that info was right there in front of me. But I wish now I had started with the stock parts to establish a base line & may still order some up.

There is also the nagging question of why the North American bikes have the different jets, given that everything else seems to be the same. I would like to try the Euro-spec Yamaha parts as well.

As for that specific Mikuni pilot, the stock TK jet is buried deep in the casting where the Mukini ends up about flush with the top of the "socket" where it screws in. I wouldn't think it would make much difference but you never know.

I think the list here will be helpful.

nwrider · Veteran Member

my local shop doesnt have part numbers on the jets, they have them by brand and size, they have the 52.5 but both a long and short, doing research online i cant seem to find a comparision to both without taking my bike apart to bring the jet down. i wanted to install jets and muffler on the same time!

TTRfan · Super Guru

RE: Jetting information

nwrider · Veteran Member

i havent, i talked to a local non yami bike mech, he said they run a little rich here in montana, and adding the q4 should make it just about right. I installed the muffler, and have had no issues, still takes a little choke to start, but as soon as i turn off, runs great, no back fires, no throttle misfiring. anything i should look for. i was told to put a new spark plug and check it for coloring or residues. true?

TTRfan · Super Guru

Just had a sort out of carb parts and I have two small round 140 Mikuni main jets.

Are these the same as the original Yamaha hex-headed 140 jets?

Brian

Butcher · Member

hi guys i took my TT-R 250 on its first long ride "under my ownership" and it was fluttering on high revs and wasnt performing well so i dicided to strip my carb down.. i had a 52.5 Mikuni pilot in there and a 140 main jet.. i consulted with a mechanic i know and he said my needle was too small for the jet.. (i've never heard that before) he gave me a 126 main jet and now the bike is moveing like a 250 but i can feel it isnt giving its all, what do i need to put that 140 back in as i have been trying to "mod" this bike up.. ive since fitted a custom power bomb to the headder and gone up on both front and back sprockets... P.S i called Yamaha and apparently there is only 1 needle size for that carb..

TDVT · Senior Member

Brian, Was wondering if you had tried the "288-" prefix jets on the list for fit, as I see you purchased at least one?

TTRfan · Super Guru

TDVT wrote:
Brian, Was wondering if you had tried the "288-" prefix jets on the list for fit, as I see you purchased at least one?

The 288 I bought was a perfect fit wink

TDVT · Senior Member

Thanks, think I might pick up a different few sizes in my carb quest. What are you running for sizes?

TTRfan · Super Guru

Jet sizing on the TTR still makes no sense to me. How can carbs with exactly the same body, slide etc run perfectly well on either 137 and 147 confuse

I have just started to refurbish a 2006 registered TTR250 that has been standing for a while and the carb was the worst I have seen - completely covered with green gunge with everything blocked and the float needle valve stuck down. I had a spare carb from a white TTR that I had just rebuilt with a 137 main jet and fitted that one whilst the green carb was left soaking. The TTR runs perfectly with it. The main jet on its original carb is 147. Go figure hmm

Unless you have opened up the airbox and/or put on a freeflowing exhaust then you shouldn't really need anything bigger than a 147 main jet IMHO.

Brian

TDVT · Senior Member

TTRfan wrote:
Jet sizing on the TTR still makes no sense to me. How can carbs with exactly the same body, slide etc run perfectly well on either 137 and 147
I have just started to refurbish a 2006 registered TTR250 that has been standing for a while and the carb was the worst I have seen - completely covered with green gunge with everything blocked and the float needle valve stuck down. I had a spare carb from a white TTR that I had just rebuilt with a 137 main jet and fitted that one whilst the green carb was left soaking. The TTR runs perfectly with it. The main jet on its original carb is 147. Go figure
Unless you have opened up the airbox and/or put on a freeflowing exhaust then you shouldn't really need anything bigger than a 147 main jet IMHO.
Brian

I find this all very confusing myself. So I'm thinking of starting over with the carb.

When I got it, my TTR had been stored for a few years & the carb & also the pet**** sound very similar to your project bike. Absolutely plugged with green stuff, the tip on the float had rotted away & what liquid there was had flakes & sediment floating in it. I put in the Mikuni jets mentioned on Thumper Talk since the originals needed to be replaced. The bike ran OK for the season but still a flat spot on the very top end, which I don't get to often anyway.

Looks like Yam #'s 146,148,150 & 152 are still available over here at powersportsplus.com. Think I might get the set along with a new main tube, needle & diaphram.

I have opened the airbox somewhat & also found a cheap WR-F exhaust I am going to try as per Matteo's thread.

bluebynature · Member

The most practical explination for the confusion on the jetting, is that the big 3 jet maufactures offer the small round jets. Keihin size runs large in number, dynojet runs in the middle, and mikuni runs small. I have been through several different jets to finally figure this out, and several hours of research.

(http://www.jetsrus.com/FAQs/FAQ_mikuni_vs_dynojet_vs_keihin_sizes.htm) offers alot of useful information. This gives you the common breakdown of the jet size conversion. (jetsrus.com) is a great resource for any future jetting information.

Sorry for the lengthy post, but not all YAMAHA dealers carry YAMAHA jets and will sell you the small round jets. Depending on what set of jets they have, as to what number works best for you. Hope this adds clarity to a foggy subject.

bluebynature · Member

http://www.jetsrus.com/a_jet_kit_dirt/yamaha_250_TTR250_2001-2005.htm

This is the closest i have found to side by side comparison of factory sizing and mikuni sizing. You would have to use both charts together to find the right combination of which jet to use.

TTRfan · Super Guru

bluebynature wrote:
The most practical explination for the confusion on the jetting, is that the big 3 jet maufactures offer the small round jets. Keihin size runs large in number, dynojet runs in the middle, and mikuni runs small. I have been through several different jets to finally figure this out, and several hours of research.
(http://www.jetsrus.com/FAQs/FAQ_mikuni_vs_dynojet_vs_keihin_sizes.htm) offers alot of useful information. This gives you the common breakdown of the jet size conversion. (jetsrus.com) is a great resource for any future jetting information.
Sorry for the lengthy post, but not all YAMAHA dealers carry YAMAHA jets and will sell you the small round jets. Depending on what set of jets they have, as to what number works best for you. Hope this adds clarity to a foggy subject.

Welcome to the forum Ron - and an excellent first post wink

It would be really good if someone could add an extra column to the table shown in your web link with the Yamaha/Teikei jets alongside biggrin

Brian

brindabella · Senior Member

I think we can agree that different brands of jets have different flow rates, and there is no good way to calculate from one to another. An equivalence chart may be useful but effective flow also depends on the actual carb, so a chart could be a bit off.

There are not many teikei carbs out there so it is no surprise that nobody sells copies of teikei jets, although they sell mikuni and keihin and copies of them.

the different types of jets do not differ just in how they are numbered, but even if they screw in properly, the internal dimensions such as length at the internal nominal diameter and chamfering on each end of the jet also differ.

so it must be guess plus trial and error to get one that works.

It is also useful to note that two jets from same maker with same number could flow differently due to manufacturing tolerances.

By the way, apparently mikuni use a different basis of numbering for round versus hex jets.

If you had two jets, one unknown (or from a different manufacturer), you could probably (if you had the time!) rig up a canister with a drain pipe and a method of holding a jet in it and time how long it takes a cup of water to drain through (repeating and averaging) and obviously the one which is faster flows more.

and now just a tiny bit of extra info about alternative yamaha main jets:

numbers 288-14329-xx and 288-14343-xx and 288-14355-xx (with extra -00 in US) may all fit a TTR250.
the xx is the size divided by 2. eg a number 148 jet would have xx = 74 (ie half of 148).
these jets are original equipment for various XT and TW models.

Andy_C · Veteran Member

Hi
I been looking at "uncorking" my ttr250 so been looking at re-jetting, started reading a brilliant post on the subject here. http://www.thumpertalk.com/topic/282432-ttr-250-modslinkspics/

One particular page in this very big topic relates to different jet sizing by different manufacturers which really cleared up a lot confusing questions in relation to what sizes of jet different people were quoting. Read this top post..... http://www.thumpertalk.com/topic/282432-ttr-250-modslinkspics/page__st__300

The link which is quoted for dyno & yamaha oem jets in comparison to Mikuni jets. http://vmaxoutlaw.com/tech/dyno-mikuni.htm

Another link with jet comparisons... http://www.4strokes.com/tech/carbjetxover.asp

This really makes sense of things for me, mikuni jets are quoted by "flow rate" and dyno/yamaha jets by the size of the jet hole diameter.

TTRfan wrote:

Just had a sort out of carb parts and I have two small round 140 Mikuni main jets.

Are these the same as the original Yamaha hex-headed 140 jets?

Brian

From the information I've uncovered Brian I would conclude its not. They equate to the yamaha oem jets of 150. The hex heads would work out between 130 and 132.5 mikuni sizes.

brindabella · Senior Member

I want to throw just a little cold water on these jet sizing charts!...

the Keihin vs DynoJet vs Mikuni sizing charts found on the internet (if correct) actually imply that NONE of these manufacturers size their jets exactly by diameter.

And to back it up, I found another chart, "Conversion Chart for Drilled Jets" on www.kawieriders.com which seems to match these charts but includes an extra column of information, namely the actual measured internal diameter of the jets.
So here are 2 rows from that chart, chosen because the 2nd row has twice the diameter [I added an extra column which is the conversion to metric hundredths of a mm]:

Width------Keihin # -- DynoJets # -- Mikuni # [mm/100]

0.0400---- 105--------- 102---------- 95.6 ---------- 101.6
0.0800---- 205--------- 182--------- 170.6 ---------- 203.2

Clearly, the numbers did NOT double when the measured jet bore diameter doubles, and the only one which comes close is keihin.

One interesting thing is that in the chart, the dynojet number with the same diameter as a mikuni jet has a totally predictable number - just multiply the mikuni number by 1.0669 to get the dynojet. So therefore IF the mikuni jets are rated by flow THEN dynojet are also rated by flow.

You won't necessarily get the same fuel flow even with the same diameters, due to other geometrical features.

Of course you cant believe anything you read on the internet (including this post of mine of course) so maybe the chart is junk or applies to only certain specific product lines from those manufacturers.

And anyway we are still in the dark as regards the orphan teikie jet numbering on our TTRs.
And that is just main jets - let alone pilot jets, needle jets / emulsion tubes!

TTRfan · Super Guru

I appreciate all the effort you guys are going to in sorting out this jetting conundrum but, meanwhile, I think I will stick to the standard Yamaha jets blankstare

I am not convinced that the TTR is that sensitive to main jet size (preparing to be shot down in flames) but my 325 didn't seem to flinch when I swapped out a 147 jet for a 137 and Adam is saying that going up from a 130 to 137 hasn't made a big difference on his 250 hmm

Brian

brindabella · Senior Member

yep, I agree, "STANDARD IS BEST" (except maybe for needle clip position)!
and if it is not working very well, then carb cleaner is the most likely fix.

but it is nice to have this site as a repository of possibly useful information for someone someday.

anyway, maybe we could have a competition for lowest and highest numbered main jet numbers for which the bike would start, run, AND reach cruising speed. but all competitors MUST specify jet brand and type as well as merely the number (otherwise it is meaningless).

no need to specify other bike changes (eg exhaust etc) as these have no real effect on performance

to set some upper and lower bounds:

(1) how does the TTR250 go with a fully blocked main jet? [jet number 0 - no need to specify brand]
(2) how does the TTR250 go if the main jet is completely removed? [jet number infinity - no need to specify brand]

actually I'm not joking, I would like to know, although I couldn't be bothered to try these two simple and zero cost experiments myself - just hoping the magic of the forum can supply an answer.

TDVT · Senior Member

I had a saved list of carb part/jets to try but when I went to order, some were discontinued. So I took the list of Yamaha jets from the beginning of this thread & Googled all the part #'s to see what what #'s are still available.

Yamaha Jets/ TTR250 in US

updated 3/13

Pilot Jets

43F-14342-24 #48 Available
43F-14342-25 #50 Available
43F-14342-26 #52 Not Found
43F-14342-27 #54 Not Found

Main Jets

288-14343-68 #135 Available
4GY-14329-69 #137 standard US Available

288-14343-70 #140 Available
288-14329-71 #142 Not Found

4GY-14329-73 #145 [AKA 288-14343-73?] 288-14343-73-00 =#146, Available
4GY-14329-74 #147 standard AU Not Found

288-14329-74 #148 [AKA 288-14343-74?] Discontinued, both numbers, possible old stock
288-14329-75 #150 [AKA 288-14343-75?] Available, both numbers

288-14329-76 #152 [AKA 288-14343-76?] Available, both numbers

This refelects what comes up in english & primarily in the US. There may be a few suppliers in Europe that have different stock.

I also found this page on motorcyclecarbs.com:

TK Large Main Jets

I haven't ordered from them & they say they might not have some part#'s in stock, though they list all the sizes right up through. They only mention TTR's at the very top, but list these jets as fitting XT350 which use the same Yamaha parts as TTR250's, so they should fit. Pretty sure this is the place that TTRKYM bought his Mikuni from that was supposed to be pre-jetted but wasn't.

-- Edited by TDVT on Sunday 10th of March 2013 09:07:18 PM

Cubber · Super Guru

Wow ........

Nice work there, Sherlock Ted. biggrin

Martyn

TDVT · Senior Member

I have decided to go one more round with the TK before I give up on it, so I just ordered the stock jets as well as the other sizes that are still available from Yamaha. I did NOT replace my main tube last time so that is also in the order.

One thing I did come across while Googling was THIS SITE with fairly extensive information about TK-22 carbs which were on numerous 80's Kawasaki sport bikes. The owner of the site has obviously done some research & the jet page (linked) has detailed cross-sections of TK jets (same dimensions as the ones used in TTR's) along with Keihin & Dynojet, which he claims ARE sized the same (in mm decimals) but are machined differently. He also mentions the Mikuni VM28/486 pilot jet (suggested in the Thumper Talk TTR jetting thread) as being unsuitable because of size & shape & Brindabella raised that point back at the beginning of this thread. The information there seems pretty thoroughly researched so I would tend to trust it more than many other sources. There is also a lenghty chart of drill sizes on the jet page.

bbarfield · Veteran Member

Hey Everyone,

I know there is a ton of info (and confusion) about jetting, size variances between manufacturers, and what part numbers are available in OEM. I've been emailing back and forth with Jetsrus.com, and let them know the Mikuni jets they show on their website as appropriate for the TTR are actually the wrong style of jet (though they may work). He informed me that they failed to update their reference page, but they now have tekei compatible jets available that will match exactly with no converting necessary. They are actually Keihin jets. The info is below. Happy riding!!

Brandon

Here is more information that may help when rejetting, we now have the main and slow jets for the tekei carb. We failed to get the page you ordered from updated but here is a link to the main and pilots we carry for teikei.

http://www.jetsrus.com/a_jets_by_carburetor_type/jets_teikei_main_hex_3T.html

http://www.jetsrus.com/a_jets_by_carburetor_type/jets_teikei_slow_3U.html

It is very helpful when folks like yourself let us know what jets they need as we will get them made if there is enough interest. I don't think many know that we have the teikei jets. Also if you are in need of other jets here is a link to most of the jets we have http://www.jetsrus.com/FAQs/FAQ_identify_that_jet.htm

Here are the correct jets for your bike, if you agree let me know and I will send the 42.5 to you http://www.jetsrus.com/a_jets_by_carburetor_type/jets_teikei_slow_3U.html

-- Edited by bbarfield on Monday 16th of December 2013 08:08:00 PM

Padowan · Senior Member

Been cleaning my jets in an attempt to sort out a dodgy idle on one of my TTRs,

On trying to clean the pilot jet and poking some copper wire through the bore it appears that there is a step inside between the threaded part and the 'holey tube' part, is that expected, the jet size is perhaps determined by only part of the bore or should the whole jet have the same bore, in which case it would appear I have some sort of restriction.

Any suggestions before I take the carb off for the 4th time this weekend!

Thanks

TTRfan · Super Guru

I just pulled out a new #50 jet and confirm there is a restriction in the middle of the jet. I can get a reamer in at both ends but there must be something like a restrictor collar in the middle. No wonder they are so flippin' difficult to clean thoroughly disbelief

You are welcome to try the new jet if you like - at least it would determine one way or the other if that was the cause of your running problems.

Brian

Padowan · Senior Member

I reckon the more aggressive cleaning has done the trick, the stranded copper I put up there did come out with some glaze/gum on and looking through the jet it definitely looks a larger opening now.

All reassembled and road tested and it all feels fine. Once warmed up (riding it) it didn't need any choke and idled smoothly with no cut outs, stutters or backfires. Pulled nicely in all gears with no bogging down or hesitation. Quite pleased!

Good to know there's a restriction in there for the future, and good experience as I reckon I can now remove the carb in about 5 minutes now, just using my trail toolkit!

TTRfan · Super Guru

Pleased to hear that Simon!

I am thinking I need to find someone with a good selection of small drill bits and find which one is the best fit in a new pilot jet and use it to check I have properly cleaned my pilot jets in the future!

Brian

Markvan · Guru

Seen this on ebay from China 3 dollars. Comes with a built in

led light and 60 times magnacation. May be handy for

checking to see if Jets are spotless. ( unless you are

superman ).

TTRfan · Super Guru

Just bought one off UK eBay - will let you know if it works on TTR pilot jets in due course wink

TTRfan · Super Guru

RE: Carb - jetting information

TTRfan · Super Guru

Bad news. I have just had an email from Fowlers to say that the #52 pilot jets are discontinued and no further stock available cry

We only had one left in stock and it's now been sold and is on its way to Australia!

Brian

TTRfan · Super Guru

More bad news as, I guess, Yamaha sell their remaining stock. #150 main jets are no longer available. I have a small number left if anyone needs one - see here - but, once they are gone they are gone

Not many options left in the genuine Yamaha jet range cry

Brian

peteBLUEttr · Super Guru

Its a shame when they have to go and discontinue oem parts and you have to knob around sourcing other gear, dont spose they can make it forever though..

coloredo · Newbie

Great site, found the carb rebuilding information very helpful. Especially comments about thorough cleaning, more of an issue for me running with Ethanol gas. I now clean using a basket in a gallon of gunk (need to remove all rubber parts first).

There are some Teikei jets available this site - www.jetsrus.com/a_jet_kit_dirt/yamaha_250_TTR250_2006.html

I have found comparable main jet performance and fit using Teikei (Yamaha, ones from jetsrus), Mikuni N102.221, and Keihin 99101-103. The Mikuni and Keihin are available from multiple dealers and online sites here in the US, lower cost than above site. All these jets fit in the Yamaha carburator. The diameter of the Teikei, Mikuni, and Keihin jets are virtually identical (photo comparison). There are dimensional differences, height, hex vs slot head, etc. which might affect fluid flow through jet orifice.

I have a couple of completely stock US 1999 TTR-250s, one used by my son. We ride 5280 feet elevation and higher in Colorado and Utah. For reference, we run a stock 50 pilot (Teikei or Mikuni VM28/486) , 130 main jet (Teikei, Mikuni N101.221 or Keihin 99101-393), needle in slot 3 (US stock position).

mossproof · Super Guru

Useful source info, thanks for adding it.

ttr steve · Super Guru

+1

I have added it to my look into list smile

Gauguin · Member

Jets available in UK

TTRfan · Super Guru

RE: Carb - jetting information

Gauguin · Member

Hi Brian,

I spoke to Fowlers earlier who could only get hold of a 147main jet ... Other sizes discontinued.

... I'm having a devils own job tuning my carb in. The bike seems to run at its best when the needle clip is on the leanest position but it's still not 100%. I'm going to try out some different jet sizes... It's my last option before taking it in to the stealers.

I've gone through the posts here extensively but to no avail...I'll type up the issue fully in a new thread and see if anyone has any ideas.

Cheers

TTRfan · Super Guru

Why not try a 137 main jet as fitted to earlier TTRs etc? See https://totallyttrs.com/epages/699105d9-e4cc-4b32-b236-84e72cd67f84.sf/en_GB/?ObjectPath=/Shops/699105d9-e4cc-4b32-b236-84e72cd67f84/Products/TTR-0512

Brian