Old School 100cc Megatopic

100cc
oldschool_100cc

(James McMahon) #1

Work in progress, figured it would be cool to have a home for the crazy revving motors from the 80’s through to 2006 ish.


Rotax DSD, 1995-1997


For senior drivers (16+) there were three main classes which were european CIK\FIA based:

Intercontinental A
Formula A
Formula Super A

ICA was reed only. Cylinder head volume and port timing restrictions. 24mm carb only.

JICA was Piston port only, 24mm carb. I think it was limited models of carb too. Walbro and baroni?

FA and FSA were rotary only until 2001 (ish). Basically once water cooled came in. Then you could pick between reed or rotary.

FA 24mm butterfly carb, FSA up to 30 and a slide.

Reeds became the dominant force by the end with the TM K11b being regarded as one the fastest 100cc of all time. 101mm conrod I think which was kinda weird.

Quite a few national champs went reed and rotary during aircooled era in a “100 libre” class. 24mm carb.


(Alan Dove) #2

that’s how we do


(Dom Callan) #3

How does the driving experience differ from a modern race kart?


(James McMahon) #4

It’s about the most perfect blend of (hu)man and machine IMO

Extremely visceral, raw and direct without being violent like a shifter. You’ve basically attached an engine and tires to your body.

Light (Race weight 320lbs).

Nimble, precise but unforgiving.

Thoroughbred, uncompromising racing machine with all of the risks/problems with being on the very edge of mechanical limits.

No clutch, direct drive. You spin, you stall. Get out and push.

No vibration dampening of the motor from the clutch either. You feel every one of those 360+ fires per second.

Maximium performance could only be found by treading the edge of destruction of the motor. Either a seize from running too lean, or a mechanical failure because some part of the motor up and quit at near supersonic piston speeds. That made racing them a real game of chess. How lean do you want to risk
it on this turn/lap?

Gear for punch out of the turns, let the motor rev as high as you dare. Modulating the peak revs with choke and/or jetting as you can, until it’s go time.
Do you want to let it run to 19/20k this lap? Are you feeling lucky?

Seize the engine…lock the back wheels, flat spot the tires.

It was rediculously extreme, totally unfair and would break your heart at (most) times.


(Dom Callan) #5

That sounds nerve wracking.


(James McMahon) #6

That too. You had to think of so much, you didn’t need gears to keep you busy.

@Terence_Dove explained the esperience better than I did in episode 22 of the KP podcast.

At least I think it was episode 22


(Dom Callan) #7

Is the weight difference largely due to safety stuff and larger displacement 125 vs 100?


(Jamie Gonzalez) #8

I found karting late in life…wishing I was around racing in 90’s.

Your statement is EXACTLY why I want to build a retro practice day toy.


(John Leah) #9

Hi all. Trundling round at the back of the u.k.100 Britain class field in 1980s we ran at 132kg. Karts were almost identical to Alan Dove’s pic above so lack of bodywork etc. contributed to the lighter weight, but the main difference came from the sheer amount of stuff we didn’t ‘cart’ about with us. No battery. No starter. No radiator No water. No clutch.

Engines were all 100cc rotary valve from various manufacturers, but no balance shafts, no water pump, no starter ring.

At the time, the top CIK international class ran 135cc engines but I doubt these were more than 1kg. heavier than the 100s.

We ran 30mm dia. axles usually 5mm wall thickness which may well have been heavier per mm. of length, but axles were shorter , hubs were short ,30 mm bearings are much lighter cf.50mm.

Then there were numerous smaller differences, shorter smaller dia. front stubs, no fully enclosed chain guards, no instrumentation, no wiring harness etc.

Add to that probably drivers were generally a bit lighter then? and we ended up about 30kg? lighter than today.


(Terence Dove) #10

Really beautifully put - we were lucky to be part of that when it was at a peak!


(James McMahon) #11

That’s a high compliment. I can’t write for :poop:.
Maybe we should make a little podcast segment out of the episode you did with Davin talking about 100’s?


(James McMahon) #12

Some of it it down to the karts, but really it’s more about culture, demographics and a sprinkle of elitism. The classes weren’t meant for everyone (although the engines were the mainstay of many nation champs across Europe).

Things were a bit more hardcore, racers were more committed as a group to get their weight down.

Since then, the sport has changed, especially with the advent of Rotax Max in 1998. The FR125 (much to the chagrin of us die hards) was a much more user friendly concept. It came along at a time when 100cc costs were getting out of hand at the top level. It’s always expensive, no matter when, but when you have 11 engines per driver, something’s gotta give.

With the Rotax Max and the other TaG formats that followed, the sport started to attract a more (serious) hobbiest demographic. One that wasn’t willing to try and race at 308lbs, or push start, or deal with motors that came apart often.

At least that’s my observation.

@Alan_Dove has some great insights in the whole scene. Drop some links Alan.

Loving the direction this topic took.


(Dom Callan) #13

As a newish karter,I cannot imagine dealing with even less reliability. Pretty much every weekend something breaks. It seems I am constantly having to fix stuff.
Everything else sounds awesome.


(James McMahon) #14

Yep. How people value their time has changed. Family unit, internet followed by social media etc etc. A lot has changed.


(Nik Goodfellow) #15

Reliability got a lot better with the rarely simple addition of water cooling. I was in 100cc aircooled for the last year and half of it and then water cooled. To be honest I can’t remember aircooled being that bad, sure they lasted an hour but you could slap a new piston and hone it yourself for (probably) less than $100 every hour and do the big rebuild every 3 or 6 hours depending on how hard you ran it or how good the engine was.

When you got to euro races though it got a little crazy, in 2002 (so watercooled days) we had three drivers doing Formula A for TopKart and we had a truck full of engines, i’d guess 50. I don’t think I did more than a session on an engine and some sessions we’d change engine midway (20min sessions). The only race we had less was Japan where we all took an engine, (drivers, drivers parents, mechanics, engine tuners) in our checked luggage.


(Jamie Gonzalez) #16

This is something I also find really weird at kart track being older and new to karting. People just dont want or know how to work on their gear. Maybe it is a generational thing but kid/teens/young adults have zero interest in the mechanical side. I see alot more kids on cell phones and push bikes instead of around the kart and doing even basic checks and maintenance. The mechanical and maintenance side is 50% of fun in my opinion but I am clearly in minority I like to tinker and spin wrenches.

I would imagine this is why tag classes took over and 100cc stuff got phased out on the recreational side of karting.


(Jamie Gonzalez) #17

In comparison to today spec tires mg yellow/Le Cont White etc…did they run on similiar tires or where they much softer?

Driving style also looks a bit different and wondering if result of direct drive or tires or chassis design.


(Nik Goodfellow) #18

Tires typically raced at that level were much softer then they are now at that level. I think they were designed to last approx 50km back then, you’d get two sets, one for qualifying and heats and one for finals. Sometime you got six tires, a spare front and back.

I’ve driven the MG Yellow and the Maxspeed Purple. I was told ahead of time the purple was really soft but i didn’t think so. I’m not convinced I’ve driven a proper soft tire since 2003. Even the Vega White (which was one of the softest when i was racing) seems relatively tame. I’m not sure how much of that is nostalgia.

I think we’ve gone over this in other threads but my belief is prior to the early noughties chassis where stiff with soft axles, now they are soft with stiff axles. The used to have built in caster of about 10-15 degrees, now its 20+. I think they got wider across the chassis rails too, someone else can chime in but I’m pretty sure they used to be 1035mm and now they are 1045 or 1050. Additionally we got a lot of “tuning” options like torsion bars, caster camber kits, larger diameter stub axles, different “stiffness” axles.


(Liam Sergeant) #19

How good would a “roundtable” KP Podcast discussing this be!?! I really enjoyed the podcast segment, but I bet there is more there. A few more voices prodding the memory banks could produce a seriously cool discussion.

(I can’t work out how to tag people, but Terrence and Davin are obviously included, and some of the voices above I bet have some emotive memories)


(Liam Sergeant) #20

I agree with this so much. Just going and doing a small job on my Kart in the garage is a hugely satisfying exercise and a great form of quiet time away from a busy life/house sometimes.