KZ vs IAME 175 SS or SSE (as the replacement to the Honda CR125)

We’ve started having a discussion in Australia (specifically our south-eastern states) for a replacement to the CR125 for our long circuit racing. Shall we say there are a range of views and there’s been some robust debate. A path forward has not been resolved.

I’m keen to hear from those users in both North America and Europe on the most recent experiences with the IAME 175 SS or SSE vs the KZ alternative (pros and cons).

North America first.

I’m well aware that SKUSA runs a mixed class with both the 175 SSE and KZ. And the AKRA for long circuits runs a mixed KZ and CR125 class over on the east coast. What I’d like to understand is if the market is moving one way or the other, and why. I’m aware of the early issues with the Tillotson carburettor (needle swap and resolved), but since then how has the 175 held up? Looking at the latest SKUSA media release, it seems to imply a further migration to KZ (notwithstanding the promotion endeavour for the SSE). Is that right or have I got that wrong? If a move away from the 175 SSE, why? Are bottom ends holding up? Is the relatively lower cost maintenance story for the SSE holding true (I hope it is)?

On the European side (and yes I know you guys run the base 175 SS with the electric start), how is support for the engine holding up against KZ? I believe in Belgium and France there seems to still be good support for the 175 SS. But elsewhere not so clear cut. In late 2019/early 2020, IAME spoke to the introduction of the combined KZ-I class - then nothing (presumably because of Covid). More recently, there is now the IAME Z-I Class (which seems to just be limited to KZ engines, particularly their Screamer, but not exclusively) - seriously confusing.

As a replacement for the CR125, the 175 SS and/or SSE story seemed to me to make a great deal of sense, particular if it meant a relatively lower maintenance regime, lower costs and less stressed engines (yes, I know, all very relative). However, is the market saying something else?

Keen to hear from users of both, pros and cons, reliability, and whether you’ve moved one way or the other, changed your mind and taken a different direction (say SS/SSE initially and then back to KZ, or the other way round) and why.


The 175 does not appear to be taking a firm position in North America. I personally love the concept and was hoping it would take off but right now I would say KZ is the preferred package in line over the CR125.

I have quite a lot of experience with the 175 SSE, and some (though less) experience with various KZ packages. Is your question of migration away from the CR125 with regards to a certain “level” of racing in Australia, e.g. National, Regional, Club? That will help inform my answers.

Hi Evan

Thank you for coming back to me.

This is coming from a long circuit racing angle rather than sprints (like SKUSA). Superkarts specifically.

We run multiple classes from 250 Internationals, 250 Nationals, 125 Open, Stock Honda (where I play) and Non-gear box running Rotax. We also run as State based volunteer organisations with a national body and broadly controlled by Motorsport Australia (mainly for insurance reasons).

So I’m talking about state run race events as well as nationals (but, as you’d expect with any state based volunteer groups, a hefty bit of politics thrown into the mix and a contest of ideas).

We stole the Stock Honda concept from the States. Great idea and the only reason I’m in karting - to run an “affordable” stock gearbox class, learn and have some fun.

The writing is on the wall with the CR125 and we need to transition. But, I would add, there is some local resistance to change and where it would leave the current drivers and their respective investment in Stock Honda. All very understandable.

My personal view is to migrate from Stock Honda to Stock Gearbox (with a mixed class of KZ, the 175 (SS or SSE) and the CR125) with some weight differences to try and create parity (albeit that want may never be perfect).

I am very attracted to the IAME 175 SS/SSE story and potential to offer the reliability and relatively lower maintenance demands of the CR125. However, because we’re moving out of the strict 125 cc space, that does create other issues and politics locally. We’re working through that and it may involve some testing late this year into next looking at comparative lap times etc.

Nonetheless, when I look at the SKUSA journey with the transition from the CR125, it appears to have not been so smooth. There seems to be a great deal of (continued) support for the KZ (but not exclusively), and there is now a mixed gearbox class.

Now, I’m very supportive of a mixed stock gearbox class here as I hope to pull in some KZ drivers from sprint to long circuit. But I also want to be able to offer more novice drivers an engine alternative to the KZ which has many of the attributes of the CR125.

What I don’t want to do through is push/encourage an engine that for some reason is not seeing market support (despite all its potential) - and/or are there any lessons to leverage off to make our transition a bit easier (and most importantly to grow the sport).

That’s the background. Keen to hear more about your experience with the SSE and why some (but by no means all) drivers are choosing KZ over the 175 SSE (in the case of North America), or vice versa.

The European journey is different again, and I’m keen to hear that too. The electric start is very attractive plus the SS derivative is already homologated in Australia, but not the SSE (yet).

Let me know what you can.


Hi Reggie

Thank you for coming back to me. Do you have any views as to why KZ seems to be gaining more market support than the 175 SSE?


Optics, IMO. The best drivers are on KZ’s, KZ’s dominate the pointy end because of it, people switch to KZ’s…

Also, not everywhere allows the 175 into the shifter class and keep it 125 only, so 1 engine in the trailer instead of two.

Don’t take my word as gospel, tho.

I really couldn’t put it any better, nor more succinctly than what Burpo did.

I think there’s also a minor advantage with the KZ for national-level races, in that it’s easier to effectively modulate power application. This can not only provide a small advantage when the rubber comes down, but also contributes to better tire wear, compounding the advantage over the length of a race day. Part of the perception that the 175 is not doing well is driven by the fact that the package has simply not had the time to proliferate the club level, so it lives and dies by what happens at the Pro Tour and Supernats. Frankly, shifter karting in the US has had a rough go in the last few years, with too many packages trying to replace the stronghold of the Honda. I see it starting to rebound at the club level, but it’s really only able to do so by having a mixed engine class or classes.

For most applications, I think that a mixed class of KZ and 175, with both running at the same weight, works perfectly fine. I’ve raced in mixed classes aboard each package, and the racing is always good between similarly skilled drivers.

The 175 SSE’s success was held back initially by some of the setbacks on IAME’s part. Once those issues were resolved the engine worked quite well for most users. There are still failures here and there, but not any more frequently than other prominent shifter engines. It’s worth pointing out that I don’t expect any shifter engine to have the reliability of the CR125…the thing is bulletproof. Part of the rub for me though is that once you taste the power of the 175 or KZ, there’s just no going back to the Honda, even if the parts WERE there.

For the 175, here are some of the pros/cons I’ve experienced in my 3 years racing aboard the package:


  • Lower upfront cost than KZ
  • excellent parity between engines
  • Carb tuning with the Tillotson is far less complex than the KZ carb
  • The power curve makes the engine SOOOO fun to drive


  • Drivability with the Tillotson carb takes some getting used to, and can be difficult for some drivers
  • Cold conditions require a slow and careful warmup procedure

I think for long track racing the 175 with the Dellorto carb would be the best fit, for various reasons.

The one glaring downside to the KZ is that not all are created equal, and it therefore takes more money in order to secure a top-level package. This is something that was similar with the Honda, but for different reasons (manufacturer tolerances), so to me it makes a package with strong parity more attractive. No one wants to feel like they’re getting beat because they didn’t spend enough money.

Thank you Matthew. Comments/thoughts noted.

Thank you Evan for the detailed considered thoughts. Much appreciated.

Two more queries.

You suggest that the Dellorto carb would be the better choice than the Tillotson for long circuit running. Can you be a bit more specific on why? In our recent Karting Australia homologation update, both carbs are available - so there is choice assuming we want to stick with the homologation framework (which for club politics, control and insurance reasons is probably the way to go). The Tillotson carb does sound attractive and it seems this is the way the Europeans are now heading with their base 175 SS (whereas previously it was the Dellorto). Do you envisage specific issues with the Tillotson on long circuits?

Finally, just on bottom end maintenance with the 175 SSE, Billy Musgrave mentioned 30 hours plus in a public article posted in early 2020. Time’s moved on. What’s been your experience? And have you seen any systemic failures with bottom ends in the 175 SSE, or is it no different/better than KZ?


Just out of curiosity, is the Rok Shifter being looked at? I don’t have any experience with the 175, so I cannot speak to that. My experience with the Rok Shifter has been very positive, with great reliability and ease of tuning. It’s not as fast as a KZ or 175, but is kind of a middle ground between those and the Honda. I haven’t done any long course with the Rok, but seeing as it doesn’t rev much above 14k should mean that it would be pretty reliable in that realm also.

On the same token, if IAME has a much larger presence there than the X30 shifter might be something to look at also. It’s a detuned KZ much like the Rok Shifter and so should benefit from the added reliability i would assume (no experience).

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The ROK shifter is a TaG-KZ package like TM has been selling, in the form of the K9ES since '06, & now with the KZ10ES. Reliability is on par with the CR. I don’t know for sure, but guessing that the ROK owes its growth to having a series organized around it. The TM seems relatively popular here in the PNW, most likely because of IM-USA being a big TM importer up here.

TaG-KZ is my preferred KZ engine/class.

Hi Ricky

Some good questions/points.

On the Rok Shifter (Vortex engines), it has been suggested by others as an alternative but as far as I know it just doesn’t figure here in Australia (nor is it homologated locally, at least as far as I know). There is some support for the Rok Mini in our sprint kart scene (and which is homologated by Karting Australia), but I think it would be a leap into the unknown for the Rok shifter (I do appreciate that this engine has a strong following in the USA).

Yes, IAME has a strong presence here in Australia with established distribution channels and support etc. So, at a level, that does make it a relatively easy choice.

As to the 125 cc X30 shifter (not the 175), that is a good question and is an engine which has also been put up as an alternative. If we were looking at a single engine stock gearbox class (which is the current situation with the Stock Honda), this could well be a good choice. However, it wouldn’t be able to compete against most stock KZ engines. I am keen to attract Stock KZ sprint drivers into Superkarts here, but at the same time be able to offer the 175 “promise” of relatively lower maintenance demands and a less “wound” engine to others. Yes, all relative.

Hopefully we’ll shortly have a dispensation here to test the 175 SS/SSE on long circuits (it’s already used here in sprints, but not widely) and get a read on lap times. One of the concerns is whether the 175 will push our 125 Open class (which often use DEA engines (circa 53/54 hp plus) with long circuit gearing and a longer chassis (Anderson etc) rather than CIK). Given the power, gearing and chassis advantages to the front runners in 125 Open, that shouldn’t be a problem, but testing required.

It may well be that we’ll need to go back and scratch our heads on the 125 cc X30 shifter, but I’m really hoping the 175 SS/SSE story holds up (and it can offer a maintenance and reliability experience similar to that of the CR125 - but yes, unlikely to quite get there as noted by Evan above).


Bottom end maintenance seems good. I’ve usually gone around 25 hours on my bottom ends in the past before rebuilding, but I’m sure 30 hours is possible. Engines weren’t going that long out of the gate, but then they figured some things out with carburation that helped. It seems like the Elf oil was also a big contributor to better bottom end life, so if it were me I would ONLY use the ELF HTX909.

The number of bottom end failures we’ve seen lately have been few and far between. I saw one that had a crank stuffer fail, which is the first time I’ve seen that in three years aboard the package. I think at this point the lower rod bearing failure rate is similar to that of the KZ. The one word of caution I would offer is to err on the side of richer jetting, as it seems the engine will still run fine under a lean condition, but will wear the lower rod bearing more quickly.

With regards to carburetor selection for long track racing, I’ll first say that I don’t have any direct experience running the 175 on long circuits, nor am I a carb/engine expert. So any speculation here is based on extrapolating my experience from sprint tracks. There seems to be a nuanced issue with the Tillotson carb that comes about on some tracks with high-speed corners, in which a lean condition occurs upon throttle application after a long full-throttle run. I’ve only experienced this at select tracks, and generally there is maximum one corner per track where the issue emerges. We’ve found a number of ways to remedy the issue within the sprint racing realm including: 1) adjust throttle application technique (most important), 2) richen low-speed needle, 3) run a stiffer inlet spring (42g or 46g).

This is a very minor issue, but I’m curious myself how the engine would perform on long circuits. Might even be worth reaching out to Billy Musgrave to see what he has to say.

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Evan, again, thank you. Very instructive comments.

Just on your last three points, you mention “adjust throttle application technique (very important)” - would you elaborate/expand.

Yes, noted on Billy. I’ve already had some exchanges with him and he has been very helpful. The more views the better though. Everyone has their own perspective.

No problem. That carb just drives a bit differently than a slide carb such as the Dellorto or Keihin in that it doesn’t allow for the “maintenance throttle” that one might do when approaching a corner (especially a fast corner). Instead, it’s import to have a more deliberate throttle input, usually meaning you have to get on the gas later. This was first explained to me by Billy Musgrave, and after changing my technique it essentially solved the issue I described earlier. Just a lot different driving style than a Honda or Rok Shifter even.

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I have run 2 seasons without opening the bottom end on 175 ss. I bought the engine used. So far this bottom end has gone through

269.5 liters of fuel (mix ratio 4.5% motul oil )
23 front tyres
28 rear tyres
seized the engine x2 (while coming off the throttle after the main straight )
dropped spark plug ground electrode and smashed the piston + cyl head x1
have accidentally run it at 100´C few times for various reasons
The engine has been detonating here and there for 1.5 seasons until I fitted a lambda sensor

Parts that have failed:
Clutch hub lost splines → no drive
starter armature bearing metallic dust shields broke into pieces and spread inside the housing

4.5% mixture is not enough, I was recommended a 5.3% mixture for mine. Also was recommended to use Elf HTX 909, it’s expensive but it provides much better protection from what I hear. In the end I think paying the $15 or so more for 909 will save you $ in the long run. It also depends though on which your running, are you running the European version with the electric start and Dellorto Carb?

Havent found any issues from running a 4.5% mix but I´ll keep your advice in mind if changing the carb etc :+1:

I have used 30% toluene mix with 98 octane while experimenting with different compression ratios. The toluene costs about 1.5€/ litre. Havent found need to use toluene if using std compression ratio head. After installing a lambda sensor havent had any piston issues

Mine is a european version with a starter and a tillotson carburetor

Given that the 175 is a bit of an oddball (Not in a disparaging way), I think I’d look at IAME’s spec shifter package… Pending some real world testing on full size tracks with the 175. One thing to consider is that the 175 has very little overrev compared to a KZ.

I don’t think there’s much (if any) data on the 175 in road racing in the US. Here’s a gear calc sheet that you make make a copy of if you want to play with numbers for gearing: IAME SSE 175cc GearCalc - Google Sheets

It’s a tough nut to crack given the mix of kart engines you have, along with bodywork. Same here for road racing. Weight makes less of an impact on laptimes since everything is so aero dependant.

The overrev improved on the 175 with the removal of the 20mm exhaust spacer. Gave it around an extra 1,000 rpm. That said, I’m sure you’ll get the usual reduction in reliability by increasing peak and average rpm (we shortened gearing after the rule change).

The closest we’ve done to road racing would be the Battle at the Brickyard (2020 config.), with peak MPH hitting around 98-99 mph. We noticed that you needed to richen the jetting pretty dramatically in order for the EGT to stay in a manageable range, but the engine performed well.

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