4 Stroke engines and karting (beyond LO206)


(Bryan Hall) #1

I’ve been looking at what engine I’d like to run for next year for road racing to replace the 80cc Honda. I’ve looked at Honda CR125R’s, KZ’s, ROC shifters, etc. Here are my notes, however misguided they may be:

Honda’s are the most reliable 2-strokes, but being old parts are getting harder to find in good condition. They don’t have as much top end as the other purpose-built kart engines, but have a little broader power band.

ROC shifters seem to be sort of in-between, but still require quite a bit of maintenance (rebuild top-end every other race).

KZ’s have the most top end HP, but are the least reliable of the bunch. Win some races, blow up and DNF others.

So what about going 4-stroke instead? Why in karting is the LO206 deemed as a good thing, but anything else 4-cycle shunned?

I saw Honda showed a CRF250R in a kart at SEMA last year. So why not run a CRF250R or something like it? New or relatively new engines so great parts availability. Similar top end power to a 2-cycle 125. Longer rebuild times (about 30 hours for ring replacement, 60 for a piston). Wide power band. And even electric start “TAG” with the newer ones.

What am I missing here?


(Curtis J Cooksey) #2

The 4-stroke motorcycle engines are pretty reliable if you leave them completely stock. If you do much to modify them the reliability goes out the window and because of the valves, cam, etc. they are more expensive to work on. I like the 2-stroke stuff for sure, replacing a piston on a 2-stroke is so easy compared to the 4-stroke. Honda parts are still easy and cheap to get. For road racing the Honda CR125 is great as long as you are in a class that limits the class to stock Honda. You can probably get a used CR125 pretty cheap right now. The SKUSA SSE 175 might be an engine that will be great for road racing too, but since I haven’t seen one road racing I don’t know enough about it.


(James McMahon) #3

I think there’s two parts to the discussion…

  1. Why aren’t there more four stroke options?
  2. What are you going to run next year (Need to know what options are available to you to answer)

On the first here’s my 2c

Which parts? My understanding is that HPD are still shipping CR125 kits. There have been a couple of supply issues in the past (That’s how we ended up with the '01+ cylinder for example), but you should still be able to get what you need for a couple of seasons.

Actually the top CR125s with an '01 cylinder have a narrower powerband compared to a KZ. It’s just that the CR’s powerband lower in the rev range. But you have to work a bit harder to keep a top level CR “on the pipe”

KZs blowing up as often as they do is a bit of a US phenomenon in my experience. They often don’t get the required maintenance and then…boom. They need more fresh parts, more often than a moto for sure.

I don’t think anybody can say conclusively why they haven’t been adopted, but here’s some of the objections I’ve observed. They may or may not be rational…

  • Initial purchase cost (Although that’s prettymuch even with a CR or KZ now).
  • Risk of catastrophic failure with gear abuse… and the cost of that failure.
  • Concerns about durability in full-on, top level racing conditions. (Look no further than how the Stock CR125 evolved from 1998 until now to see how different kart demands are vs Mx)
  • Outside the pro arena, Motocross competitors seem to typically lament the shift to four stroke. A cautionary tale.
  • Concerns about EFI trickery, trading one set of expertise (carbs) for another.
  • Resistance from engine builders who either specialize in two stroke, or OHV four stroke.
  • Weight and top-heaviness of the package.

That said. I have seen some CRF250s make an appearance in road racing in CES and the CRF450 is seeing some adoption in superkarts.


(Charles Skowron) #4

All very valid reasons, some I’ve heard before too, on why the CRF 4-strokes never gained traction over the 2-stroke CR.

You can add one more reason I remember reading in KartSport Magazine, when they tested a CFR250 powered kart, and may explain why newer 4-strokes have electric starters; they are a %*@#& to try and start without one.

And I just thought of another reason while typing this, the 4-stroke CFRs are louder than the 2-strokes. Something that is becoming more and more relevant an issue with every passing year.


(Rob Bone) #5

I choose to race a 206 because of cost and that there is a growing community in my region. WF is larger by far in the NHKA area, but we picked up a few other 206 last season. Hoping to see more come out next here. Racing Briggs is also something I’ve seen growing up and had one an old 5hp off a rototiller on my kart growing up. So partially it’s a brand and nostalgia thing for me. Briggs also is doing a great job with growing their racing program. I wish there was as level of a playing field in SCCA. SFR is close as it gets there.

The engine is rules are great and I want a solid spec class. I love knowing that I’m on a pretty much level playing field without spending a lot of money. Just comes down to setup and driving. When I win the lottery and want to go for it, 2 cycle will be an option. At least that’s where I am at, at the moment.


(Bryan Hall) #6

One of the things I see for the near future (especially in restrictive places like California) is a further clampdown on 2-cycle engines, especially in things like motorsports. While the newer TPI KTM 2-strokes may meet the requirements, older carb designs obviously do not. Agree or not that it really makes little difference overall - I’m sure a ban will happen at some point.

I’m not sure I agree that 4-strokes are necessarily louder than 2-strokes (except for motorcyclists that remove the stock equipment and basically straight pipe). Of course it does make noise at different frequencies, but that all can be dealt with easily enough.

As far as stock or not - yes, just stock is all I’m thinking about (for upright karts anyhow). The kart group here for most road races just puts all the shifters into two classes - 80 and 125, and I can see the 80 class going away RSN. So you are rather at a disadvantage if you do run a stock moto vs anything else. For sprint races at the club track, its just one class for everything.

Which parts seem more rare? Case halves and gear set parts, for when something goes knocking. They probably are available, I just haven’t ran across them other than in a used fashion - possibly because there are just enough of those still out there to not make it economical to sell new ones as the engine is sort of a “classic” parts bin now.

Thanks for the correction on the KZ engine - I wasn’t aware of that, and was actually told the exact opposite.

EFI trickery always makes me laugh. There’s no magic there at all, just maps that are spot-on for the conditions, and ones that are not. It’s a N/A engine, port FI is pretty straightforward compared to say dual port injection with a turbo. Beyond stock factory-tune class, test and tune FI just like you do with a carb - but using a phone app instead of jets.

Thanks for the feedback everyone.


(Andy DiGiusto) #7

Why not a Wankel? Ligth and powerful as a 2 stroke, simple and reliable. No need for a gearbox either. I saw one of these in action and they pull like crazy

https://woelfle-engineering.com/aixro-xr50/
or the italsistem
http://www.italsistem.com/saetta-eng.htm


(James McMahon) #8

They were imported but never really took off. I would say partly due to a lack of marketing clout, reliability issues in the beginning have them a bad rep with the higher rpm rev limiter and concerns with the massive about of heat out the exhaust.

Lastly, perhaps most importantly, like the four stroke a lack of support/interest from most engine builders.


(Jessie James) #9

I was a a track day on saterday and a couple of lads had billand sa250 , its 4 stroke two cylinder engine with 2 30mm delortos , they were not as quick as the tag karts but were close and sounded mean. The rebuild is long and whole package is similar to a tag engine.