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Discussion Starter · #1 ·
Hi all, new to the forum and a new Z125 owner! Let me start by saying I’ve always been more of a car person, this is my only road legal bike and the bike is absolutley a blast, with that said, let me apologize in advance for any ignorance, I became a gearhead later in life and hence skipped the small engine side of things and cars are what I know more about (suspension and chaisis, not so much engines which is what I’m curious about on the Z as I desire more power)

Anyways my small engine experience pretty much ends with hopping a harbor freight 212cc 6.5 hp predator motor on an old school stretched frame doodlebug minibuke up to around 18hp. Cool but seems a little more straight forward than the Z125 (at least from the outside).

So..... my main question is.... you can see all the mods I have on order in my signature, I should have everything in the next week or two..... I’m debating between complimenting with the complete 143 bbk with race head, cam and throttle body vs doing the 12:1 high compression piston and cam and leaving the stock head.... has anybody had experience with both or does anyone have dyno info on either set up with similar supporting power mods (again in my signature)? Just wondering how much difference between the 143 bbk vs the 12:1 piston and cam.

My main goal is to be able to hold 60-65 mph uphill and around a slight turn without going into a full tuck. It would also be nice to not have to run the engine at 10,000 rpm to do 65.... I live on hilly back roads and that’s where I do most of my riding, speed limit is 60 and I’d like to be able to hold that and have some more to spare. There is a lot of construction right now out my way and dump trucks riding my *** up a hill is a bit freaky. So basically looking for the most power possible.

PS: I like to overbuild things. I’m building a pro-touring chevelle right now. I made the mistake of under-buying at first, now I have 3 different coilover setups sitting in my garage, from typical bolt on “pro-touring street set-up” to full road race set up requiring extreme chassis modification. (direction I’m actually going with it), two engines, 4 different sway bar combos, etc... etc... a lot of extra parts that I will have to sell on Craigslist basically.... I would like to avoid this with the Z125 and just get it done to have some fun... so what is the verdict? Does anyone have input on if the full 143cc bbk produces ALOT more power than the 12:1 piston and cam, or do you think I can achieve what I’m trying to achieve doing the 12:1 piston and cam given the mods I have on order?

Thanks all!
 

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I have the Kitaco high comp piston and cam installed. I top out at 72mph with a 15 tooth front sprocket and 30 rear. Runs 65mph at 9000rpm. Not as much power as a 143 kit but much better than stock.
 

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from the dynos I've seen the hi cojmp piston and cam gets about 10.5 HP where the 143 and head goes to an honest 14+
 

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Discussion Starter · #4 ·
Oh wow, ok 14+ is def a bit more than 10.5, assuming stock bike is around 8-8.5 hp then that’d be around 20% gain vs a 60% gain. Thanks Greedy, I think that probably answers my question about which direction to go.

EK, with your set up, with the 12:1 piston and cam coupled with the +1 sprocket on the front, did you feel your acceleration still improved due to the power increase from the engine mods, despite the taller gearing, or is acceleration pretty comparable to stock but with a higher top speed?
 

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Discussion Starter · #5 ·
Thanks guys for yalls input, really appreciate it!
 

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The stock head on a Z is very restrictive. I wouldn’t waste the time and money on tearing down the motor and not replacing the head. Unless you were limited by cc in a race series, even then the z is the wrong bike for that sadly.
I have the full 143 kit with a few extra mods and it makes barely over 14. Stock gearing, rev extended 500rpm and a 120/80 rear tire net me 69mph top speed via gps. And it gets me there a lot faster than stock. I can cruise at 65 sitting straight up with no problem.
Whichever you decide I would recommend having a custom tune done.
 

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I'll counter with my opinion. I wouldn't bother racing the Z unless it was in a stock only class or limited to Grom/Z/Motrac/other clones. Even in 125cc restricted classes, the 5 speed in the TTR125 gives you an advantage, and the TTR125 motor isn't horrible. And if your class allows, you can run 17 inch race rubber on the L sized swingarm and forks. A cam and high compression piston with new carb and a little intake work will get you close to 12-13hp in the 125cc size. And it probably weighs in at 170 pounds. But that machine also runs in the same class as my KAYO, and I'm not ready to give up on the KAYO because it should be faster. Up the road from there is the 150cc aircooled class, that would be dominated by the Honda CRF150R engine, but that apparently bolts right up to many of the similar sized dirt bike motor mounts. So if you liked the rolling frame of your TT125, you could put either a 150 kit in it, or a 150R engine.

I see the Z and Grom as best in stock form rather than running in a modified class, I don't think they will ever evenly compete with other modified machines in the same engine size. At least in the classes we run on the East coast. They run a few other things in the South Florida arm of the organization, you can see their rules here: https://www.sflminigp.com/mini-gp-racing/race-classes/ and the NJ and NY rules are the same with no exceptions: https://www.nyminigp.com/mini-gp-racing/race-classes/ (yes it is a franchise that started in NJ). Ohio and Texas are pretty similar class structures from what I've found.

But none of those are street legal here, and getting something like that legal may be more work than it is worth. But I'm going to look into it.
 

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Since you are new to tuning bikes it might be good to start with the easy to bolt on 143cc kit, but if you like to overbuild things and you were used to an 18HP minibike then you might want to look beyond the 143cc kit and think about where you want to end up with the Z125. If you are technically skilled then I would think about the larger bore kits like the 165cc & above. They often require splitting the cases, but once you have done that, then why not throw in a 5mm stroker crank at the same time? That will give you a lot more torque than a 143cc has and torque is what you need when trying to climb hills and out running dump trucks. There is a thread on here about a 177cc build that made 17HP on pump gas, so you might want to look into that. It will cost a bit more $$$ and effort but if you can afford to buy 3 coilover setups at once then I doubt it's an issue. Besides, anything with twice the stock HP is much more fun to ride than a small bore motor. Here's a dyno chart of the stock Z125 power curves and my 173cc engine's curves for comparison. Good luck.
 

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Discussion Starter · #9 ·
Colticus, what you describe as your performance characteristics sounds very close to what I’m looking for.... Thank you very much for the input. The other concern besides being able to hold speeds of 60-65 mph is getting up to speed. My neighborhood entrance is on a 60 mph backroad with blind turns in both directions, pulling out can definitely be a bit scary on the Z, so getting there quicker would give me much more piece of mind. Given the little bit I know about motors I kind of had a hunch the big bore kit was the way to go for my application, always heard, especially when it comes to torque not just hp (torque = getting to speed vs hp = holding that speed) was there is “no replacement for displacement”, so I figured the 143cc kit would be the best of both worlds. Could I ask... do you have a 143 kit with a 2v or a 4v head? Also, are there any mods you are running that I don’t have on order (everything is in my sig) that you feel are quiticential to your performance characteristics?
 

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Discussion Starter · #10 ·
Greg_E, that is definitely something to consider and some good thoughts. I know in many applications (like my chevelle I’m building, in which was a stock 402 BBC, it was far cheaper to make near 600 horsepower and ft-lbs of torque just buying a crate 454 BBC with EFI than trying to build up that 402, it would have cost neaarly 150% of just buying the turn key crate engine to build up the 402 to that power level). I will think about that approach for sure. Very good input, thank you!
 

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I'll counter with my opinion. I wouldn't bother racing the Z unless it was in a stock only class or limited to Grom/Z/Motrac/other clones. Even in 125cc restricted classes, the 5 speed in the TTR125 gives you an advantage, and the TTR125 motor isn't horrible. And if your class allows, you can run 17 inch race rubber on the L sized swingarm and forks. A cam and high compression piston with new carb and a little intake work will get you close to 12-13hp in the 125cc size. And it probably weighs in at 170 pounds. But that machine also runs in the same class as my KAYO, and I'm not ready to give up on the KAYO because it should be faster. Up the road from there is the 150cc aircooled class, that would be dominated by the Honda CRF150R engine, but that apparently bolts right up to many of the similar sized dirt bike motor mounts. So if you liked the rolling frame of your TT125, you could put either a 150 kit in it, or a 150R engine.

I see the Z and Grom as best in stock form rather than running in a modified class, I don't think they will ever evenly compete with other modified machines in the same engine size. At least in the classes we run on the East coast. They run a few other things in the South Florida arm of the organization, you can see their rules here: https://www.sflminigp.com/mini-gp-racing/race-classes/ and the NJ and NY rules are the same with no exceptions: https://www.nyminigp.com/mini-gp-racing/race-classes/ (yes it is a franchise that started in NJ). Ohio and Texas are pretty similar class structures from what I've found.

But none of those are street legal here, and getting something like that legal may be more work than it is worth. But I'm going to look into it.
Well, I beg to differ. We have been racing a modified 125cc Z125 for the last 2 seasons out here on the westcoast and in our last 7 hour endurance race we beat a highly modified GROM(pro-built motor running race fuel, carbon fiber wheels, etc) in our 12" wheel class and only finished behind bigger bikes in the class above us with more power like the watercooled CRF150R. It's not easy and it's not cheap but the little Kawasaki motor has a lot of potential for racing so I wouldn't discount it so readily.

https://www.facebook.com/unitedminiracingassociation/
 

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Discussion Starter · #12 ·
Lobot, very good suggestions there as well, thank you! I know I would be way more pleased doing the bigger displacement kits vs 143cc kits, I will definitely put some thought into that as well! I was definitely trying to keep it purely bolt on as not to detract too much from the time spent on my car build, but at the same time, I’d hate to double buy things again. I got sick over having to do that with my car build, but.... If something is worth doing, its worth doing right! I should definitely consider that building up the Z.
 

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Discussion Starter · #13 ·
And again, want to thank everyone for their input! Really appreciate it!!

Lobot, that Facebook link looks awesome! Haven’t been on Facebook in well over a year and damnit...!!! You pulled me back!!! Worth it though, very cool!
 

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Oh wow, ok 14+ is def a bit more than 10.5, assuming stock bike is around 8-8.5 hp then that’d be around 20% gain vs a 60% gain. Thanks Greedy, I think that probably answers my question about which direction to go.

EK, with your set up, with the 12:1 piston and cam coupled with the +1 sprocket on the front, did you feel your acceleration still improved due to the power increase from the engine mods, despite the taller gearing, or is acceleration pretty comparable to stock but with a higher top speed?
I go back and forth with the gearing. The plus one is fine for the streets and on the freeway. It effects the acceleration a bit though. I did notice some nice gains with the kit but I haven't had it back to the track since I installed it. Head work is next on the list. I want to keep it a 125cc motor for racing. Opens up more classes. I will run stock front gearing at the track and try the 30 tooth rear next time out to see how it works.
 

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Colticus, what you describe as your performance characteristics sounds very close to what I’m looking for.... Thank you very much for the input. The other concern besides being able to hold speeds of 60-65 mph is getting up to speed. My neighborhood entrance is on a 60 mph backroad with blind turns in both directions, pulling out can definitely be a bit scary on the Z, so getting there quicker would give me much more piece of mind. Given the little bit I know about motors I kind of had a hunch the big bore kit was the way to go for my application, always heard, especially when it comes to torque not just hp (torque = getting to speed vs hp = holding that speed) was there is “no replacement for displacement”, so I figured the 143cc kit would be the best of both worlds. Could I ask... do you have a 143 kit with a 2v or a 4v head? Also, are there any mods you are running that I don’t have on order (everything is in my sig) that you feel are quiticential to your performance characteristics?
I have the 2v head as I will not ever buy anything from finbro and they are the only ones I could find with a 4v setup.
As far as acceleration, my setup reaches 69mph right a 1/4 mile. Video is in the link below. I did have a +2 in the rear with this setup and it accelerated even quicker. The bike would power wheelie in first gear. The +2 with the taller rear tire gives the bike an overall ration real close to stock. I mainly rock stock gearing tho as my local track is better suited with the stock gearing.
Here is a link to my build.
http://www.z125owners.com/forum/kawasaki-z125-general-discussion/14410-colts-track-build.html

As far as mods to compliment the 143, I would say the basics is all that is really needed. 143, exhaust, intake, primary gear, hd clutch, and a pcv with a custom tune. I would skip the throttle body and 300 injector. With the basic setup the bike dynoed 13.8.
 

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And again, want to thank everyone for their input! Really appreciate it!!

Lobot, that Facebook link looks awesome! Haven’t been on Facebook in well over a year and damnit...!!! You pulled me back!!! Worth it though, very cool!
Yeah, the 125cc class endurance racing has been a lot of fun and it's gotten a few of my friends to go buy Z125s and do track days with them. We have been running the Kitaco 56mm piston & cam with the stock head and the usual mods(PCV, pipe, filter, etc) so we run 13T & 33T or 34T gearing for our local 9/10 mile long kart tracks. And we run the Takegawa 6 speed which makes the most of our little 12HP motor. We're not the quickest class of bikes on track, but our corner speeds are right up there with the faster KX65s and lighter XR120s. And afterwards, I can reinstall my lights and go ride it down the street, something they can't do. I'm having a lot of fun with the Z125 these days.
 

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What mods did you do to that machine? I assume cam, compression, fuel controller, but did you do a head or work on the head?
Sorry to continue to hijack this thread, but if you are referring to my post, then yes, all of the above but with an unported TB V2 head. This was a mild pump gas build for a friend. The Z125 motor is capable of much more power than that, but the trick is building it bigger and still maintaining the reliability. That's the part that takes way more time and tuning than just bolting on the parts.
 

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Are the 143 kits from MNNTHBX and Steady Garage the same (minus the injector from Steady Garage)? $140 is quite the price difference in price...
 
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