Because he’s at 315 lbs and I would be over 400. He’s a good driver. I’m not so great. So I need something that’s faster so I can reel him in on the straights. Hopefully. 
Maybe world formula? Or build out an animal a little?
Honestly, for something that’s just to chase your kid around. I’d just put more lead on his kart on practice days, and save yourself the headache.
(Especially for what should be a fun kart, you’d be spending way more effort to build something unique, just to not drive it that much, and have to deal with so many different parts if/when the fun kart breaks.)
That or throw a World Formula on it, and then just enjoy. Much easier, in my opinion.
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Our local group runs a class with modified 420 preditor harbor freight motors. They race at 450 lb, have a field of 18-20 per race, make like 23-25hp, they are cheap and readily available and are faster than the Yamaha pipe class that I race.
Search for OVKA 420 for details.
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At Orlando Kart Center we run a “speedy” league with Honda GX 390 engine. Very reliable with speeds up to 55mph on 200 yard straights. We run sprint races and endurance races up to 12hrs. It is much more powerful and fun than Lo206. But we get the same shit here. We have 206 guys around Florida trying to talk people into 206 when the Honda 390x much faster with way more torque out of hairpins and still able to make long straights without over-rev.
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It is my opinion that any 4-stroke “hotter” than a World Formula is a grenade with the pin pulled on track.
In FSAE we used to have to choose between the 450MX singles, which have very short rebuild intervals and expensive rebuilding (<15 hours, >$1000), and the 600cc fours, which need a complete oil system redesign before they hit the track due to being straight up and down in a bike. A change to the rules 3 years ago allowed the KTM 690 single in and that’s finally an engine that will last a decent test schedule without rebuilds and blowups.
The maximum-power speed of a 2-stroke is limited by gasflow - can air get through the transfers, can exhaust blow out of the pipe, can we get a pressure wave back to the exhaust port to return the fresh mixture drawn out during expansion in time to not lose charge. The final 125-2T GP Aprilia RSA125 made 55 horsepower at 13k RPM, and that imposed only enough stress on the engine to need to change the piston in each race; Overmars and Thiel said that bottom-end work was precautionary.
In a four-stroke, adequate valve area and opening time can be provided to make mechanical failure the limit on peak-power engine speed. The stresses in a 250F MX engine can be calculated very accurately, and increased by tuning, to make them last just long enough to survive the race.
If you’d like something faster than an LO206, and do not want to buy a new chassis to mount 2 LO206s, then go get an X30 or Rotax Evo.
Honda GX 390 runs over 100hrs before needing major work. We also run it in 12hr endurance races, no issues.
John, yes. That GX390 makes 13 horsepower from 24 cubic inches, which is a little less specific output as the LO206 - it should make for a faster kart.
I think you’re mixing up what would work for you personally vs what would be adequate for the majority of racers.
We’ve had 100hp/l in production cars for 20+ years. Admittedly, there’s trickery involved to do so and the applications are different, but nonetheless I’m not convinced there isn’t room for something to provide a blend of power, ease of use as well as initial and ongoing costs.
Optimal performance doesn’t matter a lot to the masses. Ease of use is the high order bit. We know that for sure.
Thinking more about this. There’s road race class that runs built animals for 40hrs (conservatively) before top ends and makes around 20HP.
The “downside” is that they run methanol. Just making the point that you can make more power with a smaller OHV motor and still keep reliability.
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Just for fun years ago we stuck an animal coil on a World Formula and boy that thing liked the revs, made us curious about a WF outlaw class or something like that. Then we got into 2 strokes and was a moot point. I did run Burris F200 class for awhile, but they are expensive to build (fun though).
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Bring here some photos from the very intresting billand sa 250 engine for kart . And a very strange and rare for me . Never see one of those before . Sodie senna edition kart the decals write . But i couldn’t find more information about that model .
Its sure pretty
Whatever that is, I would like to drive it.
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Look at that dom .
Beautiful sound and pretty fast engine too .
Very very intresting yea !
The sodi senna edition kart is at the market for sale almost 2 years now here in greece . And i catch my self many times to think it about take that telephone and start negotiations. Hehehe…
Vroooooop,vrooooooop. Lovely!
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Since someone else revived it. Trackmagic has a thing going with the 4z190 4 stroke shifter. I really want to try one. At only 25 hp it wont beat the hell out of you. Probably still a ton of fun.
Remove the front brakes. Go have some fun.
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I might have said it in this topic already, but when tested an SA250 I was pretty impressed.
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I like the concept of a 4t horizontal shifter but I’m not sold on the Daytona having owned one. I think people are in for a bit of wallet ache if/when they start head-to-head competition. It could get to RoK costs pretty quick.
If we’ve hopefully learned anything from the last 50 years of putting bike engines on karts, it’s that all bets are off once you make that switch. Performance in karting is more engine dependent and we work engines a LOT harder at higher RPMs. Any data we have on maintenance and reliability is worthless until we get them in to tough competition.
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I’m sure. It’s racing. We will find a way to ruin reliability and cost savings.
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Briggs WF is not much more then a Lo206, however it really has never caught on in my region. I wish Briggs would seal it and roll it out. Animal Super Stock is another option that is interesting. Hard to know how Tillotson fits in, if it’s just muddying the waters. It’s a shame that Kt100, it’s nearing it’s death, wish there was some development went on to make it reliable and onboard starter like Ka100/VLR. However when people left from Clone to 2cycle nobody new came to clone and it died (until Lo206), it’s really important for tracks to recruit new karters especially the younger crowd.