Big bore 125's

[thorns]

Really needing a winter project to keep me entertained, already loosing the plot now that its dark by the time get home from work and have nothing to occupy me in the evenings!

Can anyone tell me what 125's dont require crank case mods to build them into a 144?
Has anyone on here built one themselves, and how did they turn out? Reasonably straight forward build, or a nightmare to get running right?
Would I be best just to buy an Athena kit, or is it better to send the cylinder out for boring/replating/porting at the same time?

Any companies you could reccomend who have built these before and has experience with them I could talk to?

[scott411]

Really needing a winter project to keep me entertained, already loosing the plot now that its dark by the time get home from work and have nothing to occupy me in the evenings!

Can anyone tell me what 125's dont require crank case mods to build them into a 144?
Has anyone on here built one themselves, and how did they turn out? Reasonably straight forward build, or a nightmare to get running right?
Would I be best just to buy an Athena kit, or is it better to send the cylinder out for boring/replating/porting at the same time?

Any companies you could reccomend who have built these before and has experience with them I could talk to?

i think most of them will go to 139 with out crank mods, some to 144,

appranlty the 139's run better as the still rev a bit better than the 144,

this is the company i used last, but it was over 10 years ago, i was thinking about doing a 139 to my KX125

http://www.maxrpms.com/

[thorns]

How do you find the KX125's, how do they handle compared to a RM? Doesnt seem a lot of love for them like other brands which is good because it makes them a bit cheaper.
Currently have a 12 KX450 which is the best fitting bike I have ever ridden, are the 125's suited to larger riders as well, or are they quite cramped?

[scott411]

How do you find the KX125's, how do they handle compared to a RM? Doesnt seem a lot of love for them like other brands which is good because it makes them a bit cheaper.
Currently have a 12 KX450 which is the best fitting bike I have ever ridden, are the 125's suited to larger riders as well, or are they quite cramped?

i have a KX125, but normally ride a 14 KX450F, and i had RM125's when i had the shop, the RM is probably a better bike for a taller guy than the KX, the KX125 is a bit cramped for me (im 6 foot) , the RM motor is probably faster, esp top end, the KX125 was never that quick near the end, the suzuki's turn better, but the KX's is more stable,

if you are looking for one see what you can find, and take it on condition, any of the jap 125's never really changed after 2005,

[Stylo]

i have a KX125, but normally ride a 14 KX450F, and i had RM125's when i had the shop, the RM is probably a better bike for a taller guy than the KX, the KX125 is a bit cramped for me (im 6 foot) , the RM motor is probably faster, esp top end, the KX125 was never that quick near the end, the suzuki's turn better, but the KX's is more stable,

if you are looking for one see what you can find, and take it on condition, any of the jap 125's never really changed after 2005,

Do any of the Jappa's still make a 125 ?

I know Yamaha still sell the YZ250 which is way behind anything from Europe in terms of technology but, 10 points for still manufacturing and regurgitating them.

How long that will last, I have no idea but, unless they spend some R and D coin it won't be long for sure.

04 KX500 , 01 CR500

[scott411]

Do any of the Jappa's still make a 125 ?

I know Yamaha still sell the YZ250 which is way behind anything from Europe in terms of technology but, 10 points for still manufacturing and regurgitating them.

How long that will last, I have no idea but, unless they spend some R and D coin it won't be long for sure.

04 KX500 , 01 CR500

yes Yamaha still sell the YZ125, it has not had any major updates from about 06,

[10bikekid]

I know its not a 125 but am impressed with the difference the 290 kit made to my YZF

Massive change and I had to gear it up to stop it blowing through the gears to quick even then it was pulling the front up a gear higher

139- 144 should give a 10% increase putting a modern 125 hp up to about 37 rwhp with a good torque increase, I did ride a 144 a few years ago and remember it feeling quite a bit torquer

[Jay GTI]

When I was back in the UK, I read Trail Bike Monthly (TBM), which was a bit more interesting magazine than it sounds (not much more, fark they have it hard in the UK, trail riding is NOT easy). They loved the big bore 125s and as most of the Euros make them, they decided to make their own using a YZ125. I think it was an Athena 144 kit, but don't quote me, however they couldn't get to run right, they couldn't jet it properly and it finally grenaded during a club enduro.

Each kit is different of course, but I wouldn't bother, I'd just buy a factory 150 (like the KTM150SX).

[scott411]

When I was back in the UK, I read Trail Bike Monthly (TBM), which was a bit more interesting magazine than it sounds (not much more, fark they have it hard in the UK, trail riding is NOT easy). They loved the big bore 125s and as most of the Euros make them, they decided to make their own using a YZ125. I think it was an Athena 144 kit, but don't quote me, however they couldn't get to run right, they couldn't jet it properly and it finally grenaded during a club enduro.

Each kit is different of course, but I wouldn't bother, I'd just buy a factory 150 (like the KTM150SX).

big bores can be a nightmare to jet, i have seen people have issues on 2 stroke and 4 strokes as well,

[10bikekid]

big bores can be a nightmare to jet, i have seen people have issues on 2 stroke and 4 strokes as well,

I didn't have any problems, With 4 strokes, big bores actually can run richer due to the greater suction, like having bigger lungs.

Am guessing that would be the same with the 2 stroke two, it only when people try to be to clever and run them to lean to get the last 1/2 hp or so that it might be a problem, My old KT100 2 stroke gocart had a manuel fuel lean valve that we could us to gain Hp for overtaking but you could only use it for a few secs or risk blowing the motor, 2 strokes are better off a touch rich and blubbery, its possible those mags where trying to pull everything they can out of the engine to make their mods look good on the dyno.

KTM150 would be the go yes if you got the 10k+ of coin to spare, on a budget a big bore might be just the thing

[ktm84mxc]

Husky were selling CR125's with a free 150 kit late last yr for 10g, a good deal for a new bike. You don't need to spend over 10g unless ur buying new, a 150 wont cost more then an equivalent 125 second hand. The 014 Yam YZ 125/250 look much better with the YZF plastic upgrade.