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

rattlyolddt · Senior Member

JETS!

TTRfan · Super Guru

I found the part numbers copied below for TTR jets but not many are still available.

If your TTR is on a 50 pilot and 137 main then it might be worth trying the 52 and 142 jets. MotoWard or Fowlers are worth a try. Yamaha jets are about £5-6.

I have highlighted the ones I know are available (coz I bought some) in blue.

Brian

Idle Jets

3F-14342-18-00 №36

43F-14342-19-00 №38

43F-14342-20-00 №40

43F-14342-21-00 №42

43F-14342-22-00 №44

43F-14342-23-00 №46

43F-14342-24-00 №48

* 43F-14342-25-00 №50

* 43F-14342-26-00 №52

43F-14342-27-00 №54

Main Jets

4GY-14329-69-00 №137

* 288-14329-71-00 №142

* 4GY-14329-73-00 №145

* 4GY-14329-74-00 №147

288-14329-74-00 №148

288-14329-75-00 №150

288-14329-76-00 №152

288-14329-77-00 №154

288-14329-78-00 №156

288-14329-79-00 №158

rattlyolddt · Senior Member

Cheers Brian. I'll be ringing Fowlers then.

mud · Veteran Member

Jets and where to get them

TT-R250M · Super Guru

When uncorking any bike it is not a case of ''one size fits all'', there are many factors to consider.

Main factors are- elevation, fuel quality, humidity, average temperature & of course, the modification(s) you have done to your bike.

Questions that need answering-

What size jets do you have installed now?- does it run right?

What mod's do you plan on doing to it?- details?

What is the elevation that you ride at?

What is the average temp where you ride?

What fuel do you use?- If not the usual UK Ethanol blend.

..................................................................

As you can see, without all those factors taken into account there is NO possible way to tell what jets you need.

I would give suggestions once these questions are answered, but nearly everybody around here is an expert, so you should have NO trouble wink

mud · Veteran Member

Hi Aussie pride, thanks for getting back to me.

What size jets do you have installed now?- does it run right? The bike runs well, but it is a bit slow & it's totally standard. TBH I haven't had the carb apart as I didn't want the bike off the road any longer than necessary.

What mod's do you plan on doing to it?- details? I want to uncork it as per the guide, unscrew the throttle stop, trim the snorkle, remove the exhaust restriction and that's it for the moment. Really I just want a bit more poke.

What is the elevation that you ride at? I live in the Oxfordshire, UK so we aren't very high above sea level

What is the average temp where you ride? It's freezing at the moment, and even in the summer we rarely get very hot at all. Nothing like you guys!

What fuel do you use?- If not the usual UK Ethanol blend. I use standard petrol from the pump

I hope this helps.

Cheers Mud

TTRfan · Super Guru

mud wrote:
What mod's do you plan on doing to it?- details? I want to uncork it as per the guide,............... remove the exhaust restriction............

Hi Mud

You may be disappointed as the earlier white models didn't have the restrictor fitted to the best of my knowledge but, as always, I am happy to be corrected wink

Brian

TT-R250M · Super Guru

It does not sound like you will need a much larger size from the ''mods'' that you are doing.

Pilot jet

To upgrade jets, all you will need with the set-up described is on size bigger pilot jet, but you will have to go two sizes to #52.5 because #151 pilot jets are not available. I'm not sure if your ''mods'' will be up to it without an aftermarket twin air filter, exhaust upgrade, snorkel removed but worth a shot.

Main jet

If you go up a size to #148 main jet this should be perfect. It may take a fair bit of mucking around with the needle clip position to dial it in though.

Remember: If buying jets it's not ''one size fit's all! Mikuni jets are in thoery 10 sizes larger than Teikei so if you want a #148, you would buy a Mikuni #138. I am not so sure about using Mikuni jets because the tapering may give less performance? Just a thoery.

Snorkel cut down

I have tried this twice now, both times had the same result. I tried to trim it first, it made it run rich & would splutter if I reved it past 1/3 throttle. So I trimmed some more with no luck. In the end I just removed it.

Some people ''seem'' to get good performance from the trim method but I have NEVER had success with it. That said it would be up to you what you do in that respect.

If you want to see more on jetting this carb, I have my own site that I upload this info to HERE.

I have not finished uploading & editing it all yet, but the info should be of some help.

TT-R250M · Super Guru

I thought I had better mention, if using the standard muffler (restrictive), you may only need to drop your needle clip position down to the bottom setting.

Without a twin air filter & exhaust upgrade, there would not be not a lot of difference just removing the snorkel or minor mod's. With the UK's ETHANOL blend of fuel it would make even less difference.

This is not to say that you cannot use a size bigger on main jet, but the chances are you will have to upgrade further to benifiet from this.

petenz · Super Guru

Jets

Cubber · Super Guru

Most carburettor details are here CLICKY

Which says, "early TTRs were 142 main jet and 48 pilot jet though from about 96/97 the main jet was a 147 and pilot was a 50. ("50" pilot jet is 43F-14342-25-00, "54" pilot jet is 43F-14342-27 and presumably the "52" pilot jet is 43F-14342-26-00 - about £10 each in UK).

At least one UK owner has a 96 Open Enduro with 137 main and 50 pilot jets - very confusing! However, the carbs on the blue UK/Euro TTRs I have stripped all had 147 main and 50 pilot jets and I understand that Aussie TTRs have the same. US TTRs seem to have 137/52 jets.

Johnny Davies TTR (see above) was a later model so he found a local carb specialist that did Kiehin carbs, took in his main jet and needle jet and they tried a standard round Kiehin main jet and it fitted perfectly. They measured his original jet and it was 1.47mm (apparently different makes of jets don't always mean that the no. on the jet is the size in mm) and suggested trying a 148mm, 150mm, and 152mm (Kiehin). Johnny tried them all (about £3.00 each) 148 no difference, 150 spot on, 152 too rich (like running with the choke on). Johnny has left the snorkel off the air box and has the needle on the standard position. He is looking at different needles at the moment, also he has left the mixture screw at 3.5 turns out compared to standard 2.25. The firm he used is:
Allens Performance Ltd, Unit B9, Moorbridge Road, Bingham, Notts, NG13 8GG - tel. no. 01949 836733, fax. 01949 836734
You should get better power throughout the range.

Yamaha part numbers for jets as follows (thanks to Mike Stoddard):
288-14329-71 #142
4GY-14329-73 #145
4GY-14329-74 #147"

So it's not set in stone that all TTRs have the same jets. confuse

Martyn

petenz · Super Guru

take yer pic by the look of it...

I won't really know till I have a look inside it..

thanks MR Cubber

TTRfan · Super Guru

My guess is that your mixture is weak with the GYTR on.

A quick check is to flip off the airbox cover and, if its even worse, that would confirm a weak mixture. If it ran better (unlikely) then it's too rich.

petenz · Super Guru

TTRfan wrote:
My guess is that your mixture is weak with the GYTR on.
A quick check is to flip off the airbox cover and, if its even worse, that would confirm a weak mixture. If it ran better (unlikely) then it's too rich.

Yes ... It's definitly lean..

If I have to re-jet I may aswell do the air box mod at the same time..