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Tye's 125sx+144sx =150sx build-out

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A few months ago, I needed new forks for my 2007 125sx. The forks were bent to all hell and instead of just buying forks, I bought an entire bike. It was the same year 144sx, with a bad motor, basically in pieces in a few plastic containers. I took the forks and shock, dropped them off at Factory Connection and turned my 125sx into a beautiful machine. Few months past and I decided, why not build-out the unreliable 144sx motor into a reliable 150sx?

The 144sx had a lot of problems, one of them was chopping rings, the other was a combustion chamber issue. Most importantly, the 144sx was very different then the 125sx, the carb was larger, the gearing was different, it was quite a different motor internally as well. When KTM finally came up with the right combo of rings/porting and head, they changed the name to 150sx and the final configuration was much more similar to the 125sx in 2009.

So I did some research and with the help of many KTMtalk members AND of course Andrew Cooksey (who is invaluable) I found a complete/new 09 150sx cylinder/piston and head for sale. They were first generation, but it was still going to be a lot better then the 144 parts from 07/08. Once I received the parts, I started building the motor. Because the motor I had was in pieces, stripped down to its very core, I had to pull from memory (having built the 125sx a year prior) and of course that caused some slowness. The new cylinder was mis-manufactured slightly, one of the powervalve pins needed to be bent slightly for everything to work smoothly. I was very concerned about that, but after many tests, it seemed like it would work. I also didn't have a clutch basket holding tool, so assembling the clutch was a PITA using some home-made components. But with a new crank/rod/bearings/cylinder/head/piston/gaskets/covers and almost every screw (they were pretty much all missing) I took the bucket of parts and turned it into a motor that "looked" like it was gonna work.

Its been months since I did that and I've been holding off using the newly built 144 motor because my 125 was running fine. Recently it developed a crazy bad leak out of the output shaft seal, so I decided there isn't a better time to build the new bike like the present. I start a new job wednesday and this was my last full week-day off from work for a while. The goal was to take the cleaner 144 frame/swing arm/subframe and motor and mate it with the new 144 motor and my suspension/wheels/brakes AND most importantly, the 38mm carb, which is super important to the build as the 144 carb was originally a 39mm and that doesn't work right, which is why KTM went back to a 38mm with the 150sx.

Did the build today and it went very smoothly. Moved over the entire front end as one component (without even dismantling it). Threw the new motor in the new frame, moved over my tail plastics onto the newer subframe, mounted the exhaust and did a bunch of clean-up work. I did a few compression checks cold, 160psi, which is VERY good. So I knew the motor "should" just fire up!

The first kick was nerve racking, but two kicks later it came right to life. I didn't want to put any fluids in it just incase I needed to pull it apart, but once it ran, I killed it and filled'er up and took her for a ride around the block. This motor is for sure quicker then my 125sx, I think a lot of that has to do with the "newness" of the build, where my 125 is hundreds of hours old (56hrs on piston), this new motor has a few minutes on the clock. I also think another reason is, I set the squish much tighter on the new motor, closer to "race spec" about 1mm, which of course will make it seem like its got more power.

I can't wait to ride her this weekend, its gonna be a treat to have such a nice motor. Just running her around the block brought memories of a 250cc 2 stroke, all it wanted to do was wheelies down the neighborhood streets. That to me is a good thing, and a bad thing, so we'll see if the gearing needs to be changed and wether or not the jetting is just still too lean, causing it to react with more power. Its gonna for sure take some more tuning to get right, but eventually I'll have her setup well enough to take over full-time from the 125. In the meanwhile, the 125 motor is gonna get a well deserved refresh complete with cylinder/piston/crank and rod. Its an abused little motor and I'm hoping to make it a backup just incase the 144 goes kaput! :smirk:

After the first ride, I'll be posting my next episode of "MX the beginning" full of great material about the build, so say tuned!

Thanks for everyone who helped me as well, so far so good! :bonk:

tyeworkingonmotor.jpg

Edited by tye1138
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Sounds like a sweet build. Do you have pictures of the build process?

Yep, video, pix the whole 9 yards! Though I need to edit it all together for it to make sense. So maybe next week I'll post it all. :smirk:

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really cool, give us some ride reports as well, what you think of it compared to the 125, 250 2t, and 250f. Also if you could add in what type of dirt you ride in, hard packed, sand etc. that would be awesome :smirk:

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So... went to the track saturday and to my dismay, the motor was making all sorts of strange noises and the jetting felt very far off. I played with it for at least an hour, trying to make it work better, but failed. The jingling noise coming from the right side of the cases, really prompted me to think long and hard about what I might have messed up. So I went home dismayed, took the right side main cover off to find the main crank bolt had somehow loosened itself!!! WOW, woops! I have no idea how that happened, every other nut was tight BUT that one! So obviously the jingling sound went away quick and I the motor started to sound normal. The next issue was to diagnose the jetting and I was very confused, so I first tried the 09 150 jetting settings identically and they didn't work. I then tried the 144 39mm carb with the MXA recommended jetting and it didn't work either, same problems. The motor hesitated during the needle part of the jet and had really snappy throttle response. So last resort was to throw the 144 CDI on it, something I hadn't tried yet. BAM! the thing just worked immediately! So yea, I guess KTM did change the mapping on the CDI, even though the 125 and the 144 have the same CDI part number, the actual firmware on the box must be different. Sadly the firmware number is rubbed off on the 144, so I couldn't compare it to the 125.

So I go out sunday with the hopes of actually riding the bike! Motor sounds OK (more on this in a moment) and everything else seemed ok saturday morning. First lap, bloody clutch stops working, hydraulic issue, no actuation. So I pull the cover off the master and its empty! So I threw some oil I had in there, just to give it something and it started working again after a few pumps. So I went on the track and within 2 laps, it failed again. I don't mind riding without the clutch, but to really test the bike to its full potential I needed my clutch. So after I just rode a bit without the clutch, in 35mph winds and 48 degree temp's on a super dry and bumpy track (not ideal testing conditions) I finally got frustrated trying to start the bike with no clutch. So I pulled the slave cylinder and it was full of oil! My perfectly good and working fine slave was toast! So I rode the rest of the day without the clutch not worrying about it, but sadly not able to jump in those winds, so a real test of the bike is gonna have to wait.

Initial impressions are pretty good, it does have more power for sure, but the gear ratio's are different, so I'm having to re-learn when to shift, which is annoying. I also think its pretty snappy, where the 125 was a bit more tame. I tried both the race and relaxed map, neither one was really that much different then the other. It does pull very well, as you might be able to tell from me not being able to use the clutch and still being able to ride it. So I'm somewhat happy with the upgrade, though anxious to try the 38mm carb at some point in the near future. For the time being, I've got so many other issues from bad seals/gaskets which came up during my repeated take-aparts, to some strange issues related flywheel noise. I'm getting a "woosh" noise coming from the flywheel and I've pulled it all apart several times and nothing is rubbing, nothing is wrong, but it still sounds like a bad bearing even though the bearings are new. So I'm gonna have to just ride it and see what happens! In the meanwhile. I'm gonna re-built the good-ol 125 and have it ready as a backup so when the 144 does have a problem, I'll have a backup. :smirk:

I'll be riding again this coming weekend, so I'm excited to "try again" heh :bonk:

Pix and video are gonna have to wait until then, sorry.

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So I went home dismayed, took the right side main cover off to find the main crank bolt had somehow loosened itself!!! WOW, woops! I have no idea how that happened, every other nut was tight BUT that one!

This is a common problem on the Yz smokers. I've never personally had it happen, but I use a new bolt each time, red loctite and proper torque. Some go as far as giving it a good couple second pounding with an impact.

Now post the rest of the pictures!

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Well, another weekend of riding has come and gone. Today was my only day on dirt, favoring a sport bike track day on saturday with a friend.

So today, I started the day with 14/51 gearing (I'm use to running 13/51 but the 144 comes 14/50). I just couldn't get use to the ratio's, my brain is so hot-wired to down-shift and upshift at certain speeds and with the 14/51 gearing, I was just shifting all wrong. So I moved my gearing to 13/51 and got back the feeling I was lacking previously which was nice. This also allowed me to move the wheel back a bit and put the leverage point of the swing arm further back, this helped to settle out the suspension a bit, which helped my confidence greatly. Sadly, yet again, I went to a track I didn't know, so it was another day of struggling to ride a new track, on a new bike since the other 2 tracks I know had race's on them.

As of right now, with the current configuration, I must say, I'm not so impressed. The 144 doesn't appear to have any more power then the 125, though it is a bit snappy on the throttle, which I'm sure is just a side effect of either ignition timing OR fueling being a bit lean on the needle. I did some jetting changes to try and compensate for that snappiness and did find a happy medium that seemed to be a better place.

Anyway, the bottom end needs crank bearings badly, the A-hole who sold me this bike told me he did them and I just believed him. I'm gonna order new bearings tomorrow and hopefully get them in time to tear the motor down and have it ready by next sunday. In the meanwhile, I'm gonna re-build the one-two-five and have it ready as a backup since it only needs a new output shaft seal and piston, which are both a whole hell of a lot easier then replacing main bearings.

No video this weekend, when I'm finally riding it hard enough to give you guys some good feedback, I will shoot a video. Until then... well, hold some breath! :bonk:

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Well, it seems the hard work has finally paid off. This weekend was a strange one, had to shoot a video saturday evening/night, so couldn't risk being overly tired from riding, so we played paintball instead of riding saturday. We arrived at Milestone a bit late on sunday around noon and ventured off to the beginner track for a warm up. Sadly, someone on the vet track hurt themselves, so the track was closed for an hour. So my friend Shane and I did a bitchin' moto on the beginner track, lots of fun, ate up an entire tank of fuel! We just kept riding and I started to really get use to the new powerband. When the vet track re-opened, we only had two hours until closing time to ride it, so I hit it from the get go very hard. This is a track I only knew from rolling it a few times, so for me it was a whole new situation. But having really put in some decent laps on the beginner track earlier, I knew it wasn't going to be a big deal to really throw the hammer down on the vet.

Man, I have been wrong about this motor, it really is different. After some minor jetting and suspension changes, I came to terms with the new setup and really dug it. I tell ya, my old frame must have been broken somewhere else because the suspension works very differently on this new frame, even though its the same physical components. I felt very comfortable/confident on the 144 to the point of putting in some extremely quick laps and jumping a few obstacles that last weekend would have been out of the question due to my comfort level with the new bike. But now that I've broken through that hurtle, I'm pretty confident I'll go quicker on this new bike then my old one.

So motor seems to be holding out, I'm gonna order some crank bearings just incase the noise in the flywheel area gets worse. But for the time being, I'd say she is a completed and fully functional bike.

I apologize, but I left the house today without my camera, totally spaced out on it. So I'll shoot a video filling in the whole experience for next weekend! Until then, I'm happy with the 144 and can't wait to get back on her next sat!

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Looks really good, even if it sounds like your having a lot of problems. But i bet it sounds worse than it is. :bonk:

Would love to see some more pics though

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Looking forward to it! How much harder does the 144 pull then your 125. I always ask to see receipts if someone claims they had the engine worked on.

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How much harder does the 144 pull then your 125.

Its noticeable for sure, right away the initial throttle input has more bite. I feel like I don't have to use the clutch as much and the top end of the power band seems to be a bit stronger as well. Its an amazingly different motor all the way through the rev range, which you can blame on the completely different porting, larger carb and greater compression then the 125. I don't think the bore/stroke makes THAT much of a difference, what KTM did was make a motor that wasn't anything like a 125 and they succeeded.

The stock 144 gearing sucks (14/50), in my view its unusable. It doesn't put the gear changes where you want them to be in the power band, unless you are always on the pipe maxed out. I believe the 13/51 gearing makes more sense on the 125 (not stock but is what MXA magazine likes) so I put that same gearing on the 144 and I tell ya, it resolves a lot of the complaints of the 144 riders.

In summary, the 144 is a much better package. Its not just a simple answer of how hard it pulls, because it doesn't pull that much. The answer lies in over-all power delivery, which is MUCH different then that of the 125. I'll be honest, I'm still not 100% in love with the 144 yet in terms of my jetting, but I feel its darn close and over-time I can tweak it, maybe even try the 38mm carb again, we shall see!

I always ask to see receipts if someone claims they had the engine worked on.

LOL, yea! Sadly the guys I dealt with wound up being ass-holes. I trusted them because we hung out and were friends, heck he did a lot of free work for me as well. I just found out today, the wheels I bought from the same guy who sold me the 144, are effed up, the rims are completely warped. I was wondering why I got them cheap and he said they were perfect. Wish I had the money to sue him... sadly I've gotta live with it. I'm still learning the ways of motocross and mistakes like this are bound to happen. :bonk:

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Well, here is the first video (of many) about the 144 and the build-out.

Sadly I didn't get as much useable footage as I thought, but it does have some kool shots of the build out.

Enjoy!

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awesome video and great insight into the 125 and 144. I have almost the same set up as you. I have a 2008 125sx with Factory Connection suspension. I"ve been thinking about "upgrading" to a 144 or converting my 125 for a few months now. I have a few questions if you don't mind. What needle and jetting are you running on the 125? Do you run Vertex double ring pistons? Are you using the clutch when shifting or just coming out of some corners to keep the rpms up?

Thanks man, looking forward to your next video!

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awesome video and great insight into the 125 and 144. I have almost the same set up as you. I have a 2008 125sx with Factory Connection suspension. I"ve been thinking about "upgrading" to a 144 or converting my 125 for a few months now. I have a few questions if you don't mind.

Koo and as I responded in the other thread, keep the 125! lol :thumbsup:

What needle and jetting are you running on the 125?

180 main

Stock needle 3rd ring

45 pilot

Do you run Vertex double ring pistons?

Yep, vertex pistons all the way. I've been told NOT to run the one ring pistons because they wear out more and can score the inside of your cylinder if not replaced in a very timely manor.

Are you using the clutch when shifting or just coming out of some corners to keep the rpms up?

I rarely use the clutch doing anything but building drive. Sometimes I will use the clutch in a situation where I need the extra pop DURING a shift, but is rare. 9 times out of 10, the clutch is only being used for generating drive.

Hope that helps, the next video is already in the works! :thumbsup:

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