KZ Shifter - Cost of ownership

Hopefully you can see the following:
1)a top of the line TM factory-prep is a really good quality motor, right out of the box
2)they are really solid and dependable. I did jet it a little too lean in a couple of occasions, nothing happened. They are surprisingly tolerant to screw-ups
3)Rebuilds are really cheap and do not require crazy knowledge. Just work clean, don’t use hammers or power tools…Not sure how cheaper you can get with a shifter than this
4)You can’t see it from the pictures, but I can tell you these are very, very close to those run by the top guys. Once you buy one of these you are set to be competitive, as long as you know what you are doing with jetting. Tuners have few areas that they can work on, but believe me it’s not as big of a hedge as some people make it out to be.

Hope it helps dispel some myths/rumors, I’ll add more as I hit the full rebuild milestone


So, a couple of things:

You mention you ran it a bit lean at times; do you use EGT, Computec 1000, et

Why do you think there would be such a difference in ring gap, the .23 vs .40

Do you anticipate needing to hone the cylinder any time soon, based on wear or experience?

I greatly appreciate you taking the time to document all of this.

@Andy_DiGiusto Thanks for taking the time to do both your shifter build thread (beautiful kart your built BTW) , and this Cost of ownership thread; I’ve really enjoyed reading them! :+1:

1 Like

My pleasure! I actually had the idea when I was going back and forth with somebody on the phone on ROK vs KZ, so I thought a reality check may help with some misconceptions.

1)EGT (target 1120F, spark plug reading and piston ceiling reading). I got it higher than 1,300, spark plug snow white and still didn’t seize. I didn’t run an entire session, I caught it and came back to the pits. My point is that the band is pretty wide, many people are under the impression that if you are a couple of points off then you destroy everything immediately…that’s just not the case
2)Ring gap of .23 is a result of new ring out of the box on a fairly new cylinder. I think they keep them tight to accommodate different stages of cylinder wear, you then need to gap them yourself. Since mine had barely any wear, it ended up being super tight. But I would never risk to run that small of a ring gap. Running tight gaps and thinner rings is a recipe for disaster. In theory you think you’d make more power, then you stick and make no power at all. Maybe you can find a tenth of horsepower meddling with ring gap (I would go down in steps and watch what happens to the tips), but the price to pay is not worth it for such a small gain. Thinner rings are also a no-no, 0.8 is already super thin. Lower than that makes no difference in HP, just increases the breakage rate
3)No honing of the cylinder needed. These are Nikasil-coated so you cannot bore them like you would with a conventional iron liner. They are super hard so they keep their shape and finish, while the piston wears down instead (even that, not as much as I thought). Should you have a catastrophical failure, the cylinder can then be rectified and re-coated by specialists. Frequency of that happening is pretty low for the average to advanced user


Understood, thank you!

I tend to beat this drum as lot, but TM makes a couple TaG-KZ (battery+starter) versions of the shifter engines that are more internally “regulated” (mainly via more conservative ignition parameters) that extend the maintenance intervals of these engines to schedules akin stock moto &/or the IAME SSE (but in 125cc format). They don’t top out as high as a “full-on” state-of-tune KZ motor like Andy’s, but on a more technical course, you won’t really see a performance difference; long courses are where it might show. Worth noting that because these aren’t bleeding edge screamers, so they’re more forgiving in terms of carburetor jetting relative to detonation. I don’t even mess with the carburetor settings on mine.

Having a starter is a nice luxury, & in the case of installing an electric paddle shifter like I have, an appropriate level A-hr Li+ version battery can be used to power the e-shifter box + your Mychron or Alfano, if you choose. So if you’re not wanting to have to spend & tear down with less frequency, this can be an option. Got mine at IM-USA.

1 Like

That was a killer breakdown Andy!

To simplify this for the OP, they are expensive. You will stick one. A bottom end will blow or need rebuild (this is the biggest issue IMO). Maintenance is high. Difficult to tune. Also the most fun :slight_smile:

As for tuning/jetting: agreed. It takes some time to learn and small changes can make or break your day. That’s also the beauty of it, you can have a (big) hedge over the competition once you figure it out. Not sure about the sticking and bottom end troubles…once I get to 12 hrs I will post the process and cost for a complete rebuild, including the full bottom end (it will also be surprising). When you say everybody is doomed to stick it or blow a bottom, are you talking from personal experience or from what others say? Generally or based on what you’ve seen recently at supernats or other big races?
I have a decent list of things that I’ve seen going wrong with these engines, none of them are an inherent design issue. If you think it helps, I can share a list here and let’s have a debate

Keep up the good work. As an R1 owner I am of course interested to read more about the bottom end rebuild as I only did the top end on my own engine so far.

1 Like

Most of the people that I see at the track (club level, road racing, with club racers making up the vast majority of consumers) with KZ style engines really do not have an understanding of how to run, tune or maintain them.

I see constant issues with not tuning/jetting resulting in top end seizures. Or, engines are setup on the redline and seize. Most people do not have the tools or capacity to do their own top-end rebuilds. So if you have to pay to ship an engine 2 ways (easily $200) then you now have labor and parts on top of that. Call it $500 bucks assuming no damage?

Bottom ends, Swedetech states a bottom end rebuild charge of approximately $900 plus your shipping, so let’s just call it $1,000 to be nice. In order to avoid having a potential rod failure the service interval on the bottom end is 20 gallons of fuel…

Compare this to the stock Honda. Bottom end virtually bulletproof and will last a LONG time without requiring service (i.e. multiple seasons). Top ends, depends on how much you want to squeeze out of it. Tuning much easier/forgiving compared to the KZ.

I understand why stock Honda is going away but it was a great option for the club racer/newer less experienced racer, which again IMO is probably the vast majority of karters.


Thanks for sharing, this is interesting. The bottom end interval should be 120lt or 32 gallons of fuel. That covers opening, checking, change pin, bearing, spacers, truing. If rod is ok you can run another 80lt/20 gallons with it no problem. That to me it’s a fairly decent amount of time, even if you farm it out. In a different thread about the KA100 they were talking $600 for a top end and $1000 for a complete rebuild…I will get to that for the KZ once I turn 12 hours, but it’s way less than the KA example if done (partially) by yourself, seems comparable if you give it to a tuner.

Overall I see two issues with the KZ and interestingly enough you touched on both, although with a different spin.
Engines that are setup on the edge: this is the most misunderstood part. There is a fair amount of engines around that have been brought to the ragged edge or over/badly-worked, which then get bought by customers (most of the time new to the class or new to karting) who don’t fully understand or even know about it, attracted by the idea of trying the “real deal” or by the low cost as they would sell at a discount. These engines are usually tricky and sometimes they were meant to last 1 race event only before requiring a full rebuild. I had one of those, I made it work and I totally enjoyed it, but I bet next buyer didn’t, even after my 100% transparency and disclaimers on what to expect…you sneeze, you seize :laughing: These should be just exceptions and niche situations, but I have seen too many examples of this already. I think educating people and showing some real examples can really help.

Second aspect is how to run them. Especially with TM and since the 10b came out, reliability has become a non-issue. You are right on the jetting, it’s not uncommon to see people try to go down the rabbit hole of leaning the heck out of them. That, coupled with too much oil in the mix thinking it adds a layer of safety, is a deadly combo. Then of course, you seize and blow bottoms. A standard or even factory top-tune engine is not complicated at all to run, once you get the basic things covered and they are really just few. Maybe a different thread

1 Like

Couldn’t agree more. Change the jets, the spark plug, and the gear oil now and then. That’s really it on the Honda’s. Wish there was a modern equivalent 2-stroke for 9/10s club racers.


While it may not be quite as bulletproof as the Hondas, the Rok Shifter is a very solid engine. Not near as fussy to tune as a KZ, can do long rebuild intervals. Only weak part is the shift forks, and I’ve broken them and still kept running because I was none the wiser.

Rotax/Aprilia 123. Infinite supply, option for electric start, modern ignition mapping, trouble-free exhaust valve. Can be run spec or open, can be brought up to 160cc with heaps of additional power.
Cylinder can also be flipped, looks clean and professional.
Kart 125 Rotax Special (5)

Also, I don’t want to make this thread into a KZ vs the world but what’s the value proposition here?

Even for a Stock Honda, don’t tell me it was a cheap platform when new…the new kits were quite expensive at its height of popularity.Sure now you can get used motors cheap, until you need a special spare then ouch so not really viable.

I recall there was an article from Swedetec pointing out the ICC vs stock moto cost differential was like $1,400 over a racing season. Not much to begin with. That did not include major issues, e.g. you seize hard enough, then it’s a new cylinder for a honda vs replating a KZ, that would wipe out a good portion of that cost advantage. If you are club racer or occasional driver, that differential is half as you will amortize it over 2 years of use. If you are skilled enough to do some basic maintenance, cut another half and you are down to the equivalent of one or two sets of new tires a year.

From that viewpoint, I see the ROK as a much better alternative if you want to run an engine without rebuilds for a long time. If you think about it, it 's like the OK-N equivalent for shifters, as it’s a detuned KZ engine after all. The TM10ES is the same thing, better engine platform overall in my opinion than Vortex (plus electric start), but racing support is severely lacking

1 Like

The Stock Honda was also a Nikasil coated cylinder, for what it’s worth. Stock Honda was the undisputed champ in terms of reliability, but the downfall was parity. We had seen cylinders from the same builder (consistent across multiple builders) that were 2+mph different down the straights and 0.5” over a lap. This lack of parity created made “A” cylinders go for a huge premium, which defeated the intent of the class.

1 Like

Thanks Andy, I really appreciated all the tips and info regarding the KZ maintenance interval. Is the stock carb internals from the TM KZ R1 titan need to be changed out or are they a pretty good start as a base line, at least for breaking in the engine?

True, the difference I think is rules for stock Honda called for stock cylinder only so no replating or porting or anything so once ruined, there was no option other than a new oem replacement. KZ rules allow for re-plating so no big deal there. On parity, I completely agree, spec classes always drive that cherry picking…more or less depending on the platform, stock Honda, SSE, rotax they all had that. Did stock Hondas have that deep of a variance?

Pretty close, but you will likely have to drop the max jet.

The Titan should come with the following:
Needle: K98
Tube: DP268

That is a good baseline for warm weather break-in, with the caveat that you may want to drop the max jet quite a bit after first start up and seeing how the engine reacts (about 5 points or so like a 175 is a good start but depends on many factors). During break-in, if you are not experienced, you can also opt to swap out the min for a CD1/70 or CD1/72. This will give plenty of fuel (and lubrication) at low rpm if the driver has the bad tendency to lift up for a long time and “ride the engine RPMs down”. Once the break-in is over (about 2 liters of fuel for a top end, 4 for a lower if you want to be super safe), you can swap the tube for a DQ268 and start playing around with jetting.
My go-to setting for warm to mild cold weather practice is:
[email protected]
Max 172/175/178 depending on temps (mild california weather)

I run MS98 leaded with 4% ELF 909. In order of priority, I would get max jet series from 160 to 180.Then once you get into it, optional needles K22,K23, K28 and tubes DQ +/- 2 points from the baseline above. Minimum jets +/- 4 from the baseline above. That will last you a lifetime of fiddling around. Spark plug always 105. Again, very generic indication that does not cover extremes, rain etc

The important part in break in, assuming engine is new out of the box or rebuilt with correct tolerances:
1)Pre-warm up the engine on the stand. Start it in first and keep it there. I personally don’t like leaving it in neutral and kicking it into gear later, you can literally feel the temp drop way too fast. Nice and steady warm up is better, just vary the RPMs (don’t pin it when cold…)
2)Once warmed up to 115F/120F, rev it to 10K steady for few seconds, then floor it. Once you read the max rpms, kill it with the brakes. It should read around 15k to 15.5K rpms. Any more and you are too lean, any less and you too rich. Adjust max jet accordingly. Don’t run overly-rich or put extra oil just for break-in, no real need to do that
3)Once you hit the track, simply short shift it. Don’t lift the gas, just keep it on and shift early, gradually increasing the shift points as the session progresses. Take a look at temps and EGT and your will likely be set. Like I said, if you feel like you tend to lift too long, then put a CD1/70 or 72 to help with that but really try to curb the habit
4)Max reading on the EGT should be around 1,100/1,115 F. Again, this is safe, don’t think that if you hit 1,200 the engine will granade instantly…there is still room
5)Once you end the session, check the spark plug, read the EGT data and adjust max jet from there

All of the above is a very general indication of course, erring on the safe side. The more you get to learn your specific engine, the quicker you’ll get to make changes. Check EGT, spark plug, read the piston ceiling and you will get precious data points


Your wish is granted:

Service intervals: top end @ 100-140 L (26-37 gal); bottom-end @ 400-440 L (105-116 gal).