Honda CR125 2007 tips and mods

[Critta]

hey guys i was wondering what's the best way (apart from bore kits) to get more power out of a 2007 cr125?

i'm hopefully getting one soon to race against 250f's because motocross is getting dull to be since i've been riding four strokes.. 

i currently ride a honda crf450r that is for sale..

[Critta]

[cnrcpla]

I don't think anyone is going to buy the 450f on here, unless they want the roller to put a 500 in...    And to add some power the 125, put a pipe on it. You may also want to have someone port it too, depending on how far you want to go with it. Someone else will have some more suggestions I'm sure. Good luck with it and welcome to the forum 

[Jeram]

reeds, a decent aftermarket pipe, porting, head alterations.

[Critta]

haha yeah i know that just thought i'd put it up for people to have a look (no where near as cool as a 2 stroke) but it's alright haha

yeah i'll get pipe and reeds and that sorta stuff, i used to have a '05 cr but i sold it to get a 250f.. rookie mistake that was 

[motoman356]

nice 450. ok i know this isnt the answer your looking for honestly for the cr your money would best spent on pipe silencer vforce and a 144 kit.  the CR suffered from poor case design ever since the abandoned the engine from the 97 model. The engine that the CR had from 98 and on was a rocket on the GP street bikes and in Kart racing but you dont need much bottom with total traction.

 Ive talked to many tuners and the consensus was that you could get a ton of bottom end and no top, or all top and no bottom. it wouldnt give any midrange. the cases on the motor are too big and in fact ive heard of one tuner using epoxy on the cases to "close" them up to make it more tunable but that was coming from a reputable tuner who heard another guy found a way. the 144 fits very easily on a cr due to the larger cases unlike a yz or rm that has to have the cases shaved for clearance 

since you should have a healthy budget from sellling the 450 get a big bore for the bike along with port and polish and all the other bolt on parts along with some 50/50 race fuel. this will make racing fun and enjoyable as it will allow you to have fun on your 125 and still be competitive which wouldnt be fun in last place. do it right the first time and you wont second guess the choice

[Critta]

hey mate thanks for the tip, do you know any sites or dealers that sell a kit with a good name because i used to have a 2005 cr125 and raced it for a year when i was junior then we put a 138? or something like that in it (i only ride them) but we kept having problems on the butterfly flange on the inlet? or something like that it kept on cracking?

and if you put a 144 kit in don't you have to change the bottom end also?

i'm no mechanic i'm just 17 year old kid who rides so if i say things that sound dumb that's probably why hahah
but i'm interested so tips and advice are welcome

[Jeram]

if you want more mid range thats not too hard to fix.

you just simply get the crank rebuilt will a longer rod (110mm) from another motor, and make a spacer plate thats cut to the base gasket shape (same thickness as the change in rod length).

This decreases the exh duration slightly, as the piston spends more time at TDC and BDC.

it has the effect of increasing mid rang (lower port timing) without sacrificing top end & while also making the bike reg hungry. (presumably due to both spending more 'time' prior to the exh port opening, and the increased crank case volume.

other benefits include longer piston and rod life due to the straighter rod angle and reduced piston skirt pressure against bore.


heres a bloke with a 45+ hp CR155 with a 110mm long rod

http://www.thumpertalk.com/topic/950474-thought-id-share-anotherthis-is-for-a-cr125-2005/


just depends how serious you want to go with mods.

PS: if your racing amature stuff, cant you install a 144 kit to race against 250F's?

[motoman356]

most ametuer rules allow racing 144 vs 250f's. not sure where your from so i can only recommend a few places. http://www.eric-gorr.com/ is pretty well known name on here and reputable and also http://www.maxrpms.net/shop/index.php/ has built some reliable big bores. i couldnt tell you who to go through to get the longer rod build, however i remember back in 03 the Factory Connection 125 Michael Byrne raced had this modification and that team has always had great motors

[Jeram]

most ametuer rules allow racing 144 vs 250f's. not sure where your from so i can only recommend a few places. http://www.eric-gorr.com/ is pretty well known name on here and reputable and also http://www.maxrpms.net/shop/index.php/ has built some reliable big bores. i couldnt tell you who to go through to get the longer rod build, however i remember back in 03 the Factory Connection 125 Michael Byrne raced had this modification and that team has always had great motors

you dont need a 'pro' tuner to do a long rod mod.

All you need is a crank rebuilding company to install the new rod (150 for rod, 50 bucks for rebuild), and get a CNC shop to make you a gasket via you supplying them with a base gasket (maybe 100-150 bucks)
so all up, probably 300-350 bucks to get some extra torque.

Iv got a 12.5mm longer rod (!) on my 250 Supermoto, but unfortunately I cant say what it does because it went from a 28hp enduro bike to a 45-50hp race bike in one step. All I ant say is that its the next obvious step once youve done the reeds, pipe, head, porting, carb.

[Critta]

i'm from australia and you can run up to 150cc 2 stroke against the 250f's but last time i put a bore kit in my old 125 it kept cracking a inlet flange in the head? which is apparently a common problem on the newer cr's?

doing all these mods sounds like it will make enough power but how long will the motor last?

but all these tips are interesting and very helpful thanks guys

[Jeram]

if you get the mods done by someone who knows what they are doing they can stop the exh port from cracking by:

1. welding extra material onto the back of the exh bridge and then grinding it back smooth like an aerofoil
2. they do the boring off center so the exh bridge doesnt loose any material.
3. adding oil holes to the top of the piston skirt to lube and cool the bridge, or in pistons with the holes you can enlargen the holes a little.

also running an EGT guage to help you monitor the exh temps to esure your not getting too hot. it too will save you alot of greif with cracking exh bridges.

[motoman356]

i wasnt saying you needed a "pro" to do the long rod. I pointed out that one of the few times i saw it was on a pros bike showing that it can be done and used to good effect.

the problem with long rod modifications is this practice is not practiced much and has declined with 144s being built with just a bigger piston isntead of longer stroke and bore.

also with a long rod motor wouldnt you have to also change the ports on the cylinder? unless this is what the spacer is for.

[Paul P]

I would not use the longer rod unless you want to tame (slow) the motor down. The longer rod and a spacer will give you less base compression, ( to push the fuel charge up the transfer ports into the combustion area) which makes a big difference coming out of sharp corners, and snap for big bumps or jumps. If the rod kit is 5mm longer, I would pass, if it's only 1 or 2mm longer, you may not notice it as much.
     The last CR 125 I modded was a 2001 model for a local expert. The intake track of the rubber carb intake was a lot smaller than the carb. I shaved it out to get a constant size, matched the boost ports to the cases, and roughened all the intake, transfer area's for better atomizing. Cometic used to make special gasket kits with different thickness base gaskets for more or less compression. The bike was able to run with all the other modded cr's, and walk away from the stock CR's.

[scotty dog]

i'm from australia and you can run up to 150cc 2 stroke against the 250f's

You can ride a 250 2 stroke against 250f's