Get your cylinder machined rather than buy this mass produced one. I dont think the quality is there. I would probably just take a stock 125 and do other mods to it. Not enough gain for the money imo.
Athena Big Bore Kit
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I have 2 2004 CRFs, one stock and one big bore. Big difference in power and really aggressive bark. Much more torque on hand. You have to have intake valves on spec to start the extra displacement. I may go for kibblewhite valves to keep the compression over time.
installed 4 of these kits. last kit on kx450. finished install. warmed up. cooled down. warm up. engine was quite and responsive. then I see that my engine oil is milky.. tear down. not fun the second time!! found small piece of gasket flash cut from coolant passage in center of the 3 piece head gasket. in the area between oil galley hole and coolant. see pics. contacted motosport and they helped me out and sent a replacment gasket set at no charge!!!. great customer service. replaced head gasket and ready to go!!! so check you gasket. the head gasket is a 3 piece riveted assy. just pull it open and inspect before installing.. thanks motosport!!
This was a good price and excellent investment. Put it in a CRF150RB, the power range was increased all the way around, low, mid and high. Be aware that you will need to run at least 96 octane fuel with the big bore kit.
Installed on a YZ250F. Loads of power. Was able to keep up with 450s. Easy to install. Use the circa clips provided by Athena. I made the dumb mistake by listening to a earlier review by using stock circa clips but they came out and ruined my cylinder and piston. Use Athena's. They do extensive R&D with their products to include their clips. Wasn't Athena's fault at all. All my own. Got the new (discounted) kit in there and I'm back to full power. Of course do a valve adjustment with the swap for optimal power. Now I do have hot cams so my power is extensive.
I have used the Athena kit before. The quality is the best. It does require machining of the engine case to work properly. To do it right you must split the engine cases. The performance and reliability is great. To get the most performance from the kit I used an FMF Fatty pipe and powercore 2 silencer. Jetting the carb a lot richer is a must for reliability. Installation by a qualified experienced mechanic or gear head is a must for good results.
the athena 144 kit is great! adds heaps of mid range 2 the bike and still pulls up top. However good mechanical knowledge is needed for the installation and if you cant keep your 125 on the pipe dont bother. Time with your butt in the saddle will give you far beter advantage over your competion than this kit! cheers!!!!!
this kit is great i have it on my 07kx250f it gives you tons of power. you may need to do a few other things so the bike runs right though, i had to jet mine, a bigger bowl on the carb, loudmouth intake and some fine adjustments to keep up with it. drd exhaust helped too. but once you iron out any kinks it is unreal, my friend as a 490 kit in his rmz450 and i stick with him on starts. it also runs really hot i had to get a boyesen high flow water pump to keep it cooler. best if you dont let it idle or get too hot if you stall it it will be a rough time kicking it over again.
Bought the Athena kit as a base to start a stroker build on my '07 LTZ 400. The Athena kits are really high quality, and have been around a long time. You will not be disappointed..
Nothing but problems with my new bike since installing the big bore kit. MotoSport doesn't tell you, but when purchasing this kit, you must also then spend an additional $500 in purchasing a new black box, as the stock one isn't compatible with the 290cc kit. Had I known this, I wouldn't have purchased the BigBore Kit.
bigbore kit complete and made my bike haule
i got this for my 06 yz 125 and it was definetly a waist of my money...i had to do a top end every 2 races...and then it ended up being a bottom end...i would not reccomend this to anyone...big waist of time and money...my 134 big bore has alot more power.
This kit adds huge power. Gave my lacking engine the snap and extra power i needed, it also made it sound better. It costs a little much but i would recommend it to any higher skilled or heavier rider looking for that extra power to rocket out of corners and launch over jumps you normally couldnt make.
The Athena big bore kit is an excellent bolt on for power. However.....givin the high end cost for the kit, athena has chosen to provide piston pin clips that are sub standard at best. Do your self a favor and replace the piston pin clips with factory yamaha clips instead. They fit great and will not come out. If you use the Athena clips,...you run a chance of those coming out and they will.
this was a rlly easy instaling it. the performance is rlly nice
the product is it has plenty of power. i installed this kit with hotrods stroker crank. loads of power i can now keep up with 450s off the line then naturally they stomp it in the end. but the weight to power on the trails is so much better dont get worked as bad anymore. the only down fall to the big bore is the heat it now gets so hot u cant leave it idleing for very long. if i had a second chance to increase power again i would go with stage 2 cams and a high compression piston also with the stroker crank. big bore kits arent always the way to go. hope this helps with some future ideas anyone has.
This kit is amazing! I have it on my TRX450R and I would NEVER go back! Given then only thing stock on mine is the frame, this made the biggest improvement to my bike! I love it! So, if you are looking for MAJOR power gain, this is the way to go!
This kit is a must have. Fast bolt on kit, only about an hour and half. Started first kick. I have over 200 hours on the piston with very little wear. The power increase is amazing.
I have a 2006 YZ 125 I installed the 144 kit with no problems just a bit of grinding and the rest is a breeze. No case splitting. This bike is a blast
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