TTR 125 Big Bore Kit +/-

I just installed a 150 cc BBR Big Bore Kit on my son's TTR 125 and I thought I would share some of my findings.

First let me say I have never done anything like this before and I was amazed at how simple it was. I used the Yamaha manual and was able to do this in one afternoon. It was very straightforward and I am a novice "mechanic" (using the term loosely so as not to offend a true mechanic). I left the engine attached and it with extremely minor wiggling the head bolts were manipulated out.

The biggest trick for me was the cam gear. When I took it out - I realized it was going to be a problem getting it back in. It took me about 30 mins to figure out the right combo of moves before I could wiggle it back in. TIP for those to undertake this: I lowered the gear as deep into the head as possible affording me the greatest amount of slack in the chain. Trial and error will get the gear in and low enough to accomplish this feat of mystery and magic.

I had my son by my side the whole time. I had him help with nearly everything. He was a huge help in getting the piston pin in place because that was a real 4-handed job.

We also installed a 26mm Kehin carb. No major issues. It took me a few tries to get the slider down all the way. I realized it was not bottoming out because when I started it (started second kick!) it rev'd way up and I had to kill it.

Biggest bummer for me was i was expecting mass power. The piston is dome shaped, the cam is noticeably different profile and for the money i was expecting bang for my bucks$$$$$. I rode it it and was unimpressed. My son said he could tell the difference but I think he was being nice to me.

That's my story. We went on a ride the very next day and he enjoyed the bike but he always has. He learned to do a "no footer". I unexpectedly did a "flatliner" on my YZ250F coming off a step-up jump and created an impact crater on the landing (but I lived to ride again). :D

it rev'd way up and I had to kill it.
that sounds kinda odd..something in the carb or did it just do it the first time...i have the bbr 150 and i love it i dont know if ill get the carb or not i want one but i want to get a bigger bike also

that sucks.. but after getting off my yz125 after my brother has put some stuff on his bike it still feels super slow. he says its all made a huge difference. look at bbrs dyno.. its like a 3 hp gain. so theres definately some power in there. but coming off a 250f it will still feel like a dog

I would have loved to have dyno tested this before and after for more definitive results. 3 HP is significant (33%) increase. The carb should have added a bump as well. We are trying to work with a friend of my son's to trade pipes. My son has an FMF pipe on it now and his friend has a BBR. The friend no longer rides the bike so we have a chance a straight-across trade. I ran across some dyno charts comparing the various available pipes and BBR looked best. That is the only tweak left before we get into some minor suspension mods.

that what someone rich should do is take the big bore kits and dyno the before and after.

It would be nice if a dirt bike rag did this for us. It is paid advertising for the one that comes out on top. It seems like there are endless choices and combos.

the fmf works ok for stock but once you start modding it doesn't help as much as others.. Swap out of that pipe first thing. the bbr was made for thier big bore kit's also so it is the ideal trade

Jetting makes a HUGE difference, so make sure you are jetted properly.

my freind has a bore kit in his ttr 90 and it runs like shit so if i got a bore kit i would get something diffrent than bbr

i dyno'd my stock ttr125le last year with the air box opened and carb jetted at 8.5 rwhp. i then dyno'd my ttr125le this year with a bbr big bore kit, air filter, pipe, and stock carb rejetted at 11.75 rwhp. that's almost a 40% increase in power.


I adjusted the main jet to a 112. I have not "read" the spark plug yet. We just returned from a ride a couple of hours ago and my son got major air off a few jumps. When he returned he said he could really feel the difference. I really need to at least try the BBR pipe. I will work on the trade some more. The air box is opened up all the way as well as the plastic holder. He now has air box mod, flywheel mod, 26mm carb, fmf pipe, engines-only shifter, 150cc big bore kit, TAG bars and lots of stickers!

sounds like a cool bike. i hope that all works out and you didn't waste your money. i find it hard to believe that a company as big as BBR could make a product and have it just not do anything. it would be bad rap for the company. so im sure that anybody with a big bore kit just didn't do it right by not jetting correctly or something else. thats just what i would think

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