For the record, dellorto jets don't work well in a Scorpa TK carb.  They fit, but are different.  Wanted to jet down for 5,000 ft.  Had a hard time finding TK jets.  Stock main is a 140.   Got ahold of a 132.5 that was supposed to be a dellorto jet.  It fit, but was round instead of hex.  Ran it for awhile, and watched the spark plug get blacker and blacker, then it started backfiring when I was starting it, so I pulled the carb (again) and did some testing on jet orrifices. That 132.5 has a bigger offifice than the stock 140 TK main.  Don't know how they measure them, but it was way too rich. I wanted to find some TK jets, but the usual sources kept pointing me at dellorto jets.  Finally found a TK jet source and ordered some jets to play with.  135 main jet and a 40 slow jet seem to be the ticket for my '08 SY250R at 5,300 ft.

 

Here's the TK jet source;

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

Edited November 28, 201510 yr by ridgrunr

You have the jets backwards in your head. You can get the jets from Yamaha. You are talking a 140 main(288-14343-70-00) and 36 pilot (43f-14342-18-00).

Lineaway, you're right, I got them backwards for the post.  Thanks for the heads up!  I wondered about Yamaha so I tried a local bike shop.  He said they don't deal much with jetting.  They could only look up the jet if I could tell them what type of "Yamaha" I was riding so they could look it up in the fisch. I told them I had a Yamaha Trials bike.  They said Yamaha hasn't built Trials bikes since the '80's.  Imagine the looks on their faces when I showed them my Scorpa in the back of my truck with that Yamaha embossed on the engine case! 

Oh, and I tried a 35 slow (pilot) jet.  Stumbled right off the idle when smacking the throttle.  Ran a lot crisper with the 40 piot.

These jets have been used in Yamaha`s for years and years. The TY350 had a TK carb. And yes the dealerships are useless because they are only as smart as the useless computer. All the old parts guys are gone. By the way your Yamaha engine was 15 years old in 2008!http://www.partzilla.com/parts/detail/yamaha/YP-288-14343-70-00.html

The third set of numbers, in this case the 70 is the jet size according to Yamaha part numbers. A 75 would be a 150 jet. Same with the pilots, a 20 would be your 40. http://www.partzilla.com/parts/detail/yamaha/YP-43F-14342-19-00.html

Tell that story to your Yamaha parts specialist. Back when they still printed Yamaha complete parts books it was easier without the computer. I bet the dealer actually has the mains in stock, but not the pilots. Good luck!

Oh, and I tried a 35 slow (pilot) jet.  Stumbled right off the idle when smacking the throttle.  Ran a lot crisper with the 40 piot.

http://www.trialscentral.com/forums/topic/53494-pilot-jetto-go-big-or-small-and-which-is-which-its-all-so-confusing/

If you followed my advice here, you would of tried a 42+. So how did it go?

Guess I missed that post.  Have to go back and check it.  Should try the 42 I guess, but I was having a heck of a time getting anything.  That's why I ended up with the Dellorto.  Least now I know where to get them.  The 40 seems to be pretty good, but I'm assuming the 42 would be just a tad richer?  I've got a Trials meet this Saturday.  I'll see how it feels in the sections.  Thanks for the help.

Lineaway, you are correct sir!  I should have gotten a 42 pilot jet for the 135 main.  Bike ran petty good today, but was hard to start.  Had to screw out the air screw 2.5 turns to get it to run semi decent, then it would sometimes backfire when I was kicking it to start.  In the sections though, when Ii whacked it for a wall, the 135 main ran really strong.  So a 42.5 pilot jet is on the way.  Thanks for the words of wisdom!

Our very-own (Utah's) Rocky Mountain ATV has provided me with some of these jets as well. Here's a link to their OEM TK carb parts. https://www.rockymountainatvmc.com/oem-schematic/2

utahpete, can't seem to get the link to work or find TK jets on the RM site.