4 Stroke engines and karting (beyond LO206)

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?

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.

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.

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.

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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.

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.

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

or the italsistem

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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.

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.

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This quote is from the “David Klaus from Briggs Racing - What is WRONG with karting?” topic in general - but I think it fits better here, and I’d thought I’d add an update (at least from my research) on this topic…

I couldn’t agree more, and concur with David’s points. And I’m impressed with how well that 206 program has worked.

I had somehow missed that entire thread early this year when I joined, and just read it the other day, which is interesting because it’s exactly what I’ve been thinking and doing research into. What should be next after 206, at least from currently available commercial products?

The goal of course of this is not to find the fastest possible engine. Those already exist and are great for youngsters trying to move up series. Instead, here are some of the considerations I was trying to find an alternate low-maintenance engine to meet for the rest of us:

  1. Something fun that is just (or at least nearly) as easy to run / maintain as a 206. Change the fluids at the start or end of the season, check safety items and fluid levels before each race, add gas and go have fun.

  2. A 4-stroke engine. As David said, mixing oil precisely with expensive leaded fuel, changing plugs, jets, and reeds isn’t a great selling point for most people, so something that runs on pump gas is a big plus. Plus a 4-stroke allows for a wider powerband so missing a shift isn’t a race killer. More torque is also great for those that are a little more - robust.

  3. Gears with a clutch that is forgiving.

  4. A starter is highly desirable (at least by me) so when you kill it on the grid (or after a spin), no big deal!

  5. A major manufacturer with good parts availability and dealer support is a given - so something current is preferred.

So, after a few months of research, here is my top pick, and what I’ll be working with this year - the Kawasaki EX400, the engine from the new 2018 Ninja 400 streetbike. It’s actually somewhat between a 125 and 175 peak power-wise, so that’s the class I’d run with.

  1. It’s should be easy to maintain with LONG service intervals on internals, as in several seasons I would expect, beyond the oil and filter.

  2. A newly designed light-weight (for a 4-cycle) 399cc parallel twin with fuel injection. It has a semi-dry sump (a dry sump setup with the tank inside the case) - so oil pickup should not a problem. And of course it runs on common pump gas, although 91 or 93 (altitude dependent) would be recommended for track use. And hey, with that no leaded fuel fumes and with the stock cat and muffler it’s 50 state emissions compliant and should meet all track volume limits! :slight_smile:

  3. A six speed close-ratio gearbox with a slipper clutch (slips when downshifting when the engine is much slower than the wheels), as well as assist (to lock in the clutch for less required clutch pressure).

  4. Starter - check! Combined with a lightweight lithium battery that can also power the mychron. Oh, and an alternator to keep it topped up!

  5. Kawasaki, a leader in current lightweight street sport bike engine design, with this engine being the baby and the H2R being the top dog.

Of course, getting the local race series to allow me to run it in an open, non-scored class is currently a sticky issue due to insurance regulations limiting displacement to 250cc due to 30 year old provisions. That’s rather nuts when they do allow twin 250’s that make 100 HP, but not something like this. Hopefully we can get past that soon enough so I can give this a good wringing to see if this is a good choice for 4-stroke karting to evolve and grow beyond the 206.

Another initial obstacle will be getting 428 sprockets made (520 is stock), probably in the 19t size to start with, as I have to order a lot of 100. And then fabrication of the engine mount, shifter mount, and clutch (easiest) along with all the other wire harness and packaging details.

Some of the raw specs:

Description: Twin parallel cylinders – 4 stroke
Bore: 70.0 mm
Stroke: 51.8 mm
Displacement: 399cc
Valve train: DOHC, 4 valves per cylinder
Compression ratio: 11.5:1
Lubrication: Semi-dry sump with pump and squirters
Ignition system: TCBI with digital advance
Transmission: 6 speed gearbox with wet assist and slipper clutch
Cooling system: Liquid (water with water wetter for racing)
Starter: Push Start
Fuel System: DFI with 32mm throttle bodies (2)
Max Power: 45 Hp @ 10,000 rpm
Max Torque: 28 Ft/Lb (37.9 Nm) @ 8,000 rpm
Max Rpm limit: 12,500
Weight: ?? Lbs

For reference, the new IAME X30 super shifter:

Description: Single cylinder – 2 stroke
Bore: 63.90 mm
Max Bore: 64.26 mm
Stroke: 54.40 mm
Displacement: 174.46cc
Ports: 5
Inlet system: Reed valve
Lubrication: Oil mixture
Ignition system: Analogical
Transmission: 6 speed gearbox
Cooling system: Water
Starter: Push Start
Carb. Model: HB-15A Tillotson
Max Power: 49 Hp @ 13,000 rpm
Max Torque: 27 Nm @ 12,500 rpm
Max Rpm limit: 14500
Weight: 85 Lbs

I like the concept for myself, but it’s a pretty big leap from a 206. It’s arguably going to be more abusive to the body than a typical shifter and close enough to being a superkart. I know it would be allowed at my local track in the “outlaw” class as there’s currently one guy running a CRF450 in it. But that varies from track to track.

I think a really cool concept that might work now that four cycles are cool again would be the ThumperX, lead by Maros Ambrose. I don’t think it’s an active project though.

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I think the oval guys used this motor in some outlaw uas classes. didn’t catch on and may of already been discontinued from whoever was importing them. Sounds awesome in the video though. im gonna see what I can find on it for some fun.

Probably our first independent kart track, Woodthorpe kart club, racing at Strubby started a class for Lifan pit bike engined karts ( 125cc 4/ 4speed) this year.

Sort of poor man’s version of the above at around 250 gbp for a new engine

Results show a takeup of up to ten karts with apparently no lack of reliability.

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If Briggs are interested in providing a more powerful engine to the same principles as the LO 206, they need look no further than their own Vanguard V twin.

570 cc. Air cooled 90 degree with inherent good balance. Full pressure lubrication with cartridge filter. Self

generating ignition. Twin choke carb.
The engine as supplied is fairly bulky but will run perfectly happily on a kart with all the ‘tin’ covers and the fan removed together with a lot of other surplus rubbish.

Performance is very close to Rotax Max level using a 5500 rev limit. 100% reliable with indefinite rebuild intervals.

Kart weight ready to go around 92kg /205 lb.
“Since when I have used no other!”

Something Similar to the vanguard has been around in UK and Ireland for about 20 years or so. It’s based a V twin honda GX. I can’t remember the model though. It was pretty popular, but they are pretty heavy too and ran on a specific chassis, somewhat based on a superkart.

Like you mentioned, speeds were on par with a TaG.


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Perhaps the simplest solution already exists… “built” animals. They are pretty popular in road racing.

They come in different styles, so one rule set would have to be chosen.
Power wise, somewhere in the region of about 20HP on alky reasonably reliably. You can go more than that but you’re into fun things like block bracing and so on.

The great thing of course is that you can recycle your 206 into a “built” animal.

Interesting, but all the links are dead - so I’d guess the project is the same.

I looked for a road bike engine after talking with many shop mechanics about using 4-cycle dirt bike engines and was strongly advised not to go that direction. Yes the old '80s 2-stroke versions hold up pretty good, but they mentioned that is mainly due to a lack of torque (which helps the gearbox live with sticky tires), and leaded fuel (helps mechanical lubrication). Do the same with a 4-stroke moto on pump gas and the results will likely be expensive on long WOT runs for 30+ minutes at a shot, with much more frequent maintenance and gearbox problems.

This is an interesting discussion. I’m thinking about building a kart just for fun and to chase my son around the track in his jr206. Not interested in racing.

I was looking at the lifan and briggs v twins. The lifan is $800 and the briggs is $1100. Unfortunately the lifan has a 1 1/4" crank. By the time I machined a 1" clutch I would have the same $ as just buying the briggs. My biggest concern is weight. Both weigh about 105 lbs. That’s quite a bit more than a 206 and would put me at about 450 lbs rtr or more. I would be worried about cracking frame rails with that much engine weight. Any thoughts? My other options are to get a prd or used tag.

@Kevinpitta - Why don’t the both of you just get 206s, so that both of the karts are the same, and at the very least you have a spare motor?

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^ Thats how I would do it