What do I need to know about micro/mini swift

So just picked up the kiddos new kart to practice for next year. He can’t move up yet but want to get him behind the wheel with more power and more weight. So I got a new otk with a micro swift currently. Locally we only run mini with no micro class so he will practice micro and move to mini when I think he has a good handle with the speed. What do I need to know about the swift engine.

I’ve found the Swift engines to be very reliable and robust. If you’re at all familiar with a KA100 or other IAME motors then everything will feel/work similar as well.

The biggest issue I see people having is that the motor can be finicky to start where it can be easy to flood. If your son has “happy feet” like mine and other kids where they want to stomp on the gas while pushing the starter button then this is where you’ll see kids/parents panicking on the grid when their kart doesn’t want to start.

My advice for starting is that you need to completely choke the air box off with your hand for cold starts, do not use the throttle. Since your son won’t be familiar with this it’s important to warm the kart on the stand before going out to drive or get on the grid. Once warm, just push the start button but NO THROTTLE. If you can follow that then it’ll be a breeze.

When you’re first starting you’re not going to be tuning the thing competitively so shoot for EGTs in the 900-1000 range and just make sure it’s not 4-cycling down the straights and max RPM 14k-14.5k. When you get more competitive then push those to 1100EGT and up to 15,500 for shorter/tighter tracks with longer straights as needed.

Carb- kit every 2-2.5hrs, re-torque the head 1 hour after rebuild, keep the bendix clean if buildup happens, and clean/grease the clutch after every race or practice day.

If you’re getting competitive then top ends could be necessary in as little as 5hrs, but if it’s practice time and mid-pack just keep going as long as there aren’t issues. 10-15hrs can be done in lower stress scenarios.

Have fun!


Awesome. And yeah I found out about the choking already when getting it fired. And yeah I was just treating it like my ka.

I had heard much longer between rebuilds. So that’s good to know. For now this is just a practice motor. So no stress there. And I’ll eventually get a second motor to aid in rebuild schedule.

I appreciate all the other info. And can’t wait to see his reaction moving up from a comer kid kart.

These kids pumping the throttle like a madman and then fouling out the engine on the grid drives me nuts. And there’s always a few dads going into a full panic attack on the grid because of it.

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I cant even keep my kid’s foot off the gas when I am pulling the string on his 4 cycle…

I have found a quick pinch on the big toe usually reminds him enough. He then gives me the “sorry dad” eyes and shoulder shrug :slight_smile:

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I can relate. Sitting on grid shouting “Jerry!!!, starter!!!”

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Guess I’m lucky. I have the opposite problem. I can’t usually get him to use the throttle when I want him to in grid.

We created a rule. Visor up only do what I say. Visor down it’s switch to grid steward.

But he is still 5. So I’m sure it will eventually switch away from that as he gets older.

What Chris said, but I try to keep the EGT a little lower.

The only times I had problems on the grid was when I didn’t warm on the stand. If it does flood, you can pull the hose from the carb to the engine and crank until the fuel spits out and the engine makes an attempt to start. Then reconnect the hose and try again.

Keep the battery charged. It may sound like it will fire up, but it won’t. We started with a smaller battery and upgraded rather quickly.

After a carb kit or engine swap, pull the airbox and cover the carb with your hand until fuel comes out. It will be get things flowing even faster.

Hope this helps!

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From my experience when we ran the Mini Swift (and now are in KA100), is that the Swift is just a mini KA. The biggest things to remember, is as you adjust the needles, a small turn does a lot when tuning, so don’t go crazy with your adjustments, no need to do more than 1/16th at most.

Secondly, as mentioned above, is choking the motor to start. That is the biggest error I see people doing when their motor won’t start, they try choking it more, which in turns causes them to actually flood the motor. On a typical club day, you may only need to choke it for the first start of the day. Always start it in the pit before the grid, and first attempt try without choking. If it doesn’t start, then try a small amount of choke and it should start. If you get into this habit, you’ll never need to choke it on the grid. Just don’t over choke it.

As far as rebuilds, they are robust little engines. The last Swift we ran had 20 hours on the bottom end and 2 on the top end when we sold it, and the person I sold it to put another 20 hours on it before sending in for a rebuild. Just before it was sent in, they were setting track records with it, even with all the hours on it. The builder said the motor was in great shape when he took it apart, and said everything looked great. We always ran 8 oz. to 1 gallon.

Also, I know your son is still learning on it, but the target is to keep the low RPMs above 7500 if possible, but under 15000. That’s the range the motor works best in. If I am not mistaken, the micro restrictor will cause the motor to drop 500-750 rpm on the top end, but we never ran it as a micro.

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Topic a little old, but I think my question fits in the “what do I need to know…” vein.

Looking at getting my 11YO into Mini Swift next year. I’ve talked to a few folks that race them nationally and have heard several variations of “there can be large differences engine-to-engine”.

I see a lot of engines for sale on Friendbook / Marketspace, and many of those with national/reputable builder stickers on the side. Also, a lot of photos have the serial number of the engine, and occasionally something like “…coveted R number” or “desirable Z number”.

Anybody in the know on these engines willing to share thoughts on A) how variable they really are, and B) tips on identifying a good one?

I recommend a handheld starter. Use a Zippy 8400 mAh LiFePO4 battery and solid aluminum bus bars; that motor and battery combo will start a Corvette with 100 times the displacement of a MiniSwift.

Regular compression checks will let you know when the engine is worn out enough to lose power. 5 psi loss is noticeable underfoot. WOT and ground the plug to the cylinder. Do it at the end of the day and you won’t be out there with your ball home desperately trying to fit and break in a new piston before qualifying.

There can be large differences from driver to driver and how the chassis is set up.

You shouldn’t worry about your engine unless the driver is very close to the top. Rent from someone reputable like Woltjer and if the kiddo puts down a lap on par with the fast kids, buy it off of him. But when someone is selling a motor who is staying in that class, you have to wonder why. Or when someone is selling 9 motors with 1 hr on them.

I know people don’t like to talk about it, but there are engine builders still floating around (and probably never went away) who are known to cheat but the engines are getting through tech. And yes, there are people still buying 10 engines and bolting them all together for a mega motor. Who has what at a national level? I don’t know, but don’t assume that sticker on the side of the engine was the last shop to work on it.

Has your son been karting in other classes previously or this will be his first go of it? Are you planning on racing locally, regionally, or nationally?

Plenty of builders can put together a competitive mini, but the higher level masses seem to have gravitated toward Woltjer to the point that the only new business he wants to take on are mini/micro motors.

If you’re at the pointy end of the field I have found as Charles mentioned that the motors are more sensitive to compression for every last ounce of performance which shortens the top end intervals for highest levels of competition. That means 4hrs or less for competitive local or regionals and fresh top ends for any national.

However if you’re mid pack and your son is still learning how to use the brakes as required in this class and how to maximize his line, then you can send the motors with 10-15hrs because the fall-off after that initial compression loss is minimal.

If you want a competitive motor that you know you can trust? Call Woltjer and have him build you a new one. No history or stories to worry about, and he won’t sell you junk.

If it floods out while trying to start it just pinch/fold the fuel line until it fires, then should be fine. Generally should start with no effort, if it doesn’t fire then Cover the intake until it fires then it should go.

Generally gear it in the 14k range.

Thanks fellas. My son has 3 years of cadet experience in LO206, so while there will surely be a driving (and mechanic) learning curve we aren’t starting from zero.

I don’t expect our local class will be large or overly competitive as clubs go - it averages 14 LO206 Sportsman per race but it will probably be more like 5 Mini Swifts next year. But we may well hit a Route 66 or USPKS race or two next summer in addition to the club racing.

Sounds like punchline is get a motor or two from Woltjer and send it.

If you’re inclined to save a bit of money then buy one from Woltjer and use only for race days. Buy another used of the many you see floating around to put the bulk practice hours on. You may get lucky that the used one is a rocket, but even if it’s off the pace it won’t matter as it’s the sacrificial lamb keeping time off your race motor. It also serves as a backup or parts source if you have troubles on race day.

That sound like a pretty good plan.