Jetting on TTR125

[oabike]

I just pulled the snorkle and cut a great big hole in the top of my airbox.The bike breaths good but now it is a little too lean. Can anyone suggest any jetting changes. I've already heard 110-115 main but what about the others? I'm at sea level and 70 deg year round.

 

[stormer94]

I put the BBR pipe on ours, it's got the 112.5 jet now, did the aribox mod's I'm happy as a clam.:)

Bob

 

[ACS]

With an openeded up exhaust 112 or 115 would be about right. I would go the 115 as you are at a low level and warm.

 

[bulldog71169]

I am about the same level and temp as you here in N. CA and started with the 110... but was a bit lean. I recently put the 112.5 in and she is running like a champ now, although still a hair lean. I will try the 115, but I'm affraid it will be a bit rich.

I have opened up the airbox, and have the BBR pipe installed, btw.

 

[oabike]

Thanks, I'll grab a 112.5 today. Has anyone messed with the pilot jet,needle jet or the pilot air screw?

 

[bulldog71169]

I am no wrench so I have been following BBR's recomendations. They have not been able to dial it in right with the stock carb if you change pilot or needle position, so I have left well enough alone. I know they have gone up to a 120, depending on the riders style. If you are running wide open 90% of the time then you do want a larger main. But I want to be able to put around at the same time without fouling plugs constantly.

 

[ACS]

The standard carb is pretty small but works good. I tried adjusting the needle etc and it made the bike run not as well. This was on stock bike with airbox opened and standard exhaust unplugged. If you go with pipe, lightened flywheel and other engine stuff a bigger carb works really well but then you find the limits of the CDI and head design.:(

A side note is that I talked to the development guys at Wolf ignitions which are sold in USA as FMF (orange box ones) about new cdi. They would probably be willing to build them but is there any interest?

 

[oabike]

I put in the 112.5 main today and it runs great. My hand is currently in a cast so the bike will see a lot of use next week when the pins come out. The little thumper should help my timing before I hit the track again. Thanks for your help.

 

[simimi]

112.5?

Hello,

I have the air box mods, bbr exhaust, airbox mods, and flywheel done and am still finding it running cold blooded.

I called the dealer and he had 110, 115, 120 size jets, but no 112.5 Where are you finding the 112.5? Is it a stock type of jet I can find at parts stores???

thanks,

Mike

 

[bulldog71169]

most shops can order the half sizes mike. I never did find anyone with them in stock tho. BBR sent one to me. but anyone should be able to order it for you. Are you going to ClubMoto tonight? I will be there around 5:30-6:00 depending on traffic, but not riding tonight.

 

[LocoCD]

Most of the shops around here cary them, go to any shop - not just the Yamaha Dealer and ask for a large round Mikuni 112.5, they are fairly prevelant.

We have 2 TTR 125's, one with an FMF pipe and the other with a Pro Circuit T-4, the 112.5 jets seem to be spot-on.

 

[deadhead]

My 2001 TT-R has the stock pipe with the PowRoll Thrust Chamber extension. I've also drilled six quarter-inch holes around the outlet into the spark arrestor so she'll push a larger volume of exhaust, while keeping the spark arrestor functional. I've removed the airbox snorkel and drilled 2 one-and-a-half inch holes in the airbox. This allows me to run a small sheet of foam filter at the top of the airbox, without it getting sucked in.

Anyway... Every dealer I've been in (I check Yamaha parts places whenever I travel on business) asks me for a part number. I don't have one, so they ask me if it's slotted or hexed. I haven't actually taken the main jet out yet to show them--I don't feel like taking the carb apart only to be told they don't have what I want in stock.

Can one of you tell me what the part number for the 110 is? I take it a "large round Mikuni..." as posted by LocoCD indicates it's slotted.

Thanks.

deadhead

 

[simimi]

I do not know a part number but stopped at my local aftermarket shop and asked for a "large Round Mikuni, 112.5" and they pulled out a small box and had a whole selection. Aparently the Large is the key, they make small also.

mike

 

[simimi]

air screw

I have changed jets, but am new to this "tuning thing".

what are you running the air screw at?

Mine has all the mods, BBR exhaust, air box, flywheel, etc, but it still runs supper cold and can be tempermental to start. I tried the needle one step richer but when my daughter putt-putted around it fouled a plug.

I am back to stock on the needle, running a 110 main. will the 112.5 help the cold starts?

Any tips appreciated.

ps. my yz400 is a one kick wonder, hoping to get the ttr as dialed in too!

 

[bulldog71169]

I didnt even check to see where the mixture was... I simply left it alone. Mine has gotten easier to start over time and when I put in the 112.5 main , it did start a little easier... but ran a lot better on the top end.

 

[ACS]

The TTR is a cold motor to start. I remember that the choke has to be on for ages with the stock setup. I think its the tiny carb they come with and lean jetting that is stock especially as you open up the airbox and exhaust. I foud that it started easier after it had done a fair bit of work. A bit like the YZF's.

Bigger carb cam etc and they are still take a long time to warm up. You adjust the airscrew to whatever suits the particular bike where you are. The YZ250F/YZ426 guys spend ages checking out each others airscrew settings and its a lot of garbage. Jetting specs can vary a bit, sometimes a lot from bike to bike and if you want to be really fast you should jet on the day for temp, altitude etc etc. The air screw should be adjusted to get the bike idleing as smooth as possible by adjusting the idle on the slide stop then adjust the airscrew then the idle stop then the airscrew an keep on going and get the best and smoothest idle then richen a tiny bit and it should now idle perfectly and rev cleanly. Its a fiddle thing not a 1.75 turns out thing.:)

I have tried different grades of plugs to see if I could jet differently but the stock seems best but for a stock bike just plugging around a try of a hotter plug could be worth trying for the few $$$ they cost. Be careful though if you then go out and thrash it as the plug could melt things.:eek:

 

[Idaho Charley]

Hard starting? Up your pilot to a 17.5 pilot - at lower elevations you may even want to up it to a 20 size. We live in Idaho and ride at 5000 feet and up. I raised the clip on the needle one - lowered the main to a 100 - increased the pilot to a 17.5.

Mods - air box opened, lighten flywheel, 14T spocket, opened stock exhasut snorkel to 1.1 inches and installed a thrust chamber - runs strong from idle to WOT rpm.

 

[simimi]

what is the desc. or part number.

Cool, good info about the pilot jet.

What type/size of jet is it? If I can find one I will try it out.

Mike

 

[Idaho Charley]

Don't have a Yamaha part number for the pilot jet. If you look in your owner's service manual on page 4-4 the pilot jet I mentioned is item number 15 located adjacent to (i.e. recessed hole) the main jet. Just remove it and take it to any place that stocks Mikuni carb parts and ask for the next size up. You may even want to buy the next two sizes up (17.5 and 20). Install the new pilot jet and warm up the bike; then adjust the pilot air screw identified as item 18 on page 4-4.

Although the pilot air screw is somewhat of a pain to get to I just made a small straight screw driver tool (about 2 inches long) from a piece of 1/8 inch welding rod. i.e. touched one end to a grinder on opposite sides and then clipped the rod to the length I needed. Reach in and tune away. I start with the air pilot screw open about one and 1/2 turns and try to find the adjustment which gives the fastest slow idle then I turn the air screw in 1/4 of a turn: It just seem that the throttle response off idle is better when I do this. My boy's bike can now come off the choke much sooner without bogging or killing the motor under a light load. Also starts with 2 or 3 kicks when cold where before we were stroking maybe 12-15 times before it would light-up.

BTW - Noted that a number of the posts seem to indicate that their bikes would not rev out. After making our initial mods - air box, opening the snorkel, etc. our bike would also studder at high rpm and not run clean. I verified there was no rpm limiter via the dealer and then went ahead with a plug check. Plug check indicated rich on the main, so we went down in sizes until it ran clean which was with a 100 main and I could likely go to a 97.5 main. Just to clairify we do ride at much higher elevations (5000ft) than many of you and we have not gone with an after market pipe which can drastrically change jetting. The bike really revs and we have not noticed any valve float or any sort of studder at high rpms; the bike just builds power to a peak then power tapers off (bike is screaming) and it is pass time to shift.

Hope this helps!!

 

[destructo]

I am no wrench so I have been following BBR's recomendations. They have not been able to dial it in right with the stock carb if you change pilot or needle position, so I have left well enough alone. I know they have gone up to a 120, depending on the riders style. If you are running wide open 90% of the time then you do want a larger main. But I want to be able to put around at the same time without fouling plugs constantly.

I run the 20 pilot and the 112.5 for the main, removed the intake air tube and mounted a UNI filter right to the carb, mine flys, throttle response is awesome. Dont change any needle settings it will work perfect, starts awesome runs perfect, im at sealevel to here nc. The 115 made it start to loose power, kinda bogged.