Open KPV - 108cc / Margay Brava 1.2 Build Log

GoKart Projects & Restorations
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This build started in late 2012 or so. I was fascinated with autocrossing, most of my friends and social culture came from cone dodging. But I was ready to move on to something different to really try to win some events. So, I’ve purchased an old dusty Margay kart from a buddy and started my journey.

In retrospect, that was the wrong baseline for an autocrossing kart altogether and it would most likely have never been successful. But I was just starting with this karting thing and truth be told, I wasn’t fully invested in real karting as a sport, and didn’t know nearly enough.

Most of my knowledge for this build came from my experience with Nitro 2 stroke RC cars. With nearly 10 years of experience with those little engines, I had good knowledge of everything ranging from how to calculate and design tuned pipes to how to do port work. I love 2 strokes, and most of this stuff is very much second nature for me.

Naturally the first thing I did was to blast the kart around my neighborhood. In the winter. At temperatures below 10 degrees. Then immediately started tearing it apart: Shimmed the head to reduce compression, colder spark plug in, RLV A3 pipe was installed, retarded the ignition some, and formulated a 15% nitromethane emulsion. Didn’t change anything on the Walbro WB3-A carb but the needles and jetting. :grin:

We took the kart for a few test laps at Norway, my first time on that kart track. It pulled like a monster, clutch burning and the motor zinging all the way to 21,000 RPM :brap: Results were… Predictable?

r

…Perhaps just a result of gross inexperience?

…Or of too much enthusiasm?

I’ve murdered that engine. It was fantastic. :sunglasses:

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That happy “accident” became the start of something wonderful. The true beginning of my karting obsession was the teardown and rebuild of that KPV motor.

I’ll keep updating this thread, it came out quite special. :slight_smile:

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I’m impressed it held together long enough to burn a hole in the piston.

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KPV @ 21k RPM = LOL

Poor little engine. Interested in seeing where this goes!

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Oh it was great.

I first took it to the track with the guy I’ve bought the kart from, might have been more clueless about what he sold me then I was about what I bought.

Engine was singing at 19.5k RPM all day without much of an issue. I started thinking, those things were never supposed to spin that high were they?

My friend then says the engine was rev limited to 18k RPM, the tach wasn’t working right, and I should just push it all the way.

… And push it all the way I did! :joy:

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The teardown begins… In my basement bedroom at my parent’s house! I’ll keep this as detailed as I can so people can learn a thing or two about opening up KPVs. But keep in mind this was 5 years ago and the engine was sold in 2014! So let’s go:

Clutch drum comes out. This was pretty straight forward: There is a KPV-specific (or rather, Hortsmann EXP-D clutch-specific) holder wrench you can buy to hold the crank in place from the clutch end. It goes behind the clutch. NEVER remove the crank nut while holding the crank steady from the ignition rotor side, or you may knock one of the crank ends off balance!

When you remove the crank nut, the drum, washers, and needle bearing should come out. Parts are lined up in sequence:

Hold the HPV/KPV Sellettra ignition rotor steady using an ignition rotor wrench or a rotor puller. Remove the ignition rotor nut, then pull ignition rotor out using the rotor puller. Or you can make your own!


Clutch pack needs a puller, too. But this one you’re better off buying.

Remove the motor mount.


Removing the head and the cylinder is a piece of cake. Get the 4 head nuts out, and both the head and the cylinder slide out at the same time.

Keep everything organized…

Cracking the crank open requires a sturdy piece of metal and some careful prying. But it isn’t too hard. Slide the crankshaft/piston assembly out, and tada! You’re done!

To remove the old piston from the rod/crankshaft assembly, remove the circlips from the piston wrist pin cavity and slide the wristpin out, being careful NOT to disassemble the top rod needle bearings from their cage. That bearing goes between the piston wrist pin and the small end of the rod.
Should be pretty easy.

I had decided to send the cylinder and head out to Laukaitis Racing in Decatur IL for a couple of reasons: They came highly recommended (and I wasn’t disappointed, to be honest. They did good work), and I didn’t know about Viking Karting Products which was a lot closer to me.

I’ve bought a new piston and packaged it up to ship with the cylinder and head to Laukaitis: A BIG 55mm overbore KT100 piston from Burris Racing. It only had 1 piston ring instead of the standard 2 on a stock KPV piston, but my research showed that it shouldn’t matter much.

Here’s a comparo of the 2 pistons after trimming the piston skirt to keep port timing. In the end the port timing wasn’t right, so I needed to trim it more before final assembly:

To be continued…

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Laukaitis did an excellent job with the bore and head…


Not a whole lot of pictures from the assembly process, but it was painless and simple. Just put everything back together like it was. All done! The special-order K&N filter was the icing on the cake.

Took the kart out to CHMS for a few laps on my nitromethane/methanol/ gas emulsion in preparation for my first autocross event with the kart. Had to take some head squish out and install my fresh 27mm IBEA Yellowpower triple jet carb for more fuel, replacing a worked version of the stock Walbro WB3A…

But otherwise it went surprisingly smoothly. The day was beautiful and I was the only one practicing at the track. About 40 laps later… “Just a few bucks and I can lap all day in this beautiful track? What am I doing with this autocrossing BS?”

The karting bug was starting to bite hard…

Neverthless, I shook off my feeling of switching my motorsport devotion to karting. Autocrossing is where my heart was.

My Hegar 4 fairing was installed.

My first autocrossing event lineup looked competitive. But my kart felt fast. I thought I could do it. (Really!)

It ran, at least.

For those unfamiliar with the sport: In autocrossing, you race a total of 6 (or if you’re lucky a few more) laps in a parking lot course set up with cones. Lap times are about 1 minute long. You race against the clock, and people compete for the fastest time in their classes. You are penalized if you knock a cone off the course markings with time penalties.

Every 3 laps, you have a break and a work assignment. You work collecting the cones other people hit, and calling out penalties over the radio so it is heard by those keeping track of people’s lap times.

The six laps went fine, but slow. I could not throw competitive times and I was becoming disenchanted with my machine.

Tried the autocrossing thing for another couple events. Event #2 went much the same as event #1, even though I had modified the stock KPV EXPD clutch to get a super aggressive engagement at 6000 RPM.

My last event was frustrating beyond belief. The first lap went like usual, but I ran into carburation problems during the following laps and could not complete them. It became impossible to tune the carb and set up the kart with such little track time.

Then it was time for my work shift. I was already becoming increasingly frustrated. When the time came for my next 3 laps, I ran into problems with carburation AGAIN and couldn’t even leave the start/finish line.

I had just spent over $50 and nearly 10 hours of my time for about 1 minute of track time, and that was unacceptable.

To be continued…

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I did an autocross once and felt the same way. It’s a lot of time for not a lot of seat time. Even the convienince of having one seven miles away from my house wasn’t enough to tempt me to try again.

Don’t get me wrong, it wasn’t a “bad” experience, but for the time and effort it made more sense to drive 90mins to the sprint track.

Sidenote: I drove from the house to the AutoX with a GoPro resting on my roof. No, not mounted, just placed there :stuck_out_tongue:

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Ironically I’ve ended up buying a house 3 miles (3!!!) from my old autocross hotspot, so sometimes nostalgia hits really hard.

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I knew I liked karts, but after my autocross experience I didn’t know if I liked the sport that much. I started a new build over the winter, without any particular endgame. At that point I just wanted something different, I wanted to see what I could do and how far I could take the Margay. I had nothing to lose.

That project was initially based on my nitromethane powered KPV. However, the universe had different plans when I ended up stumbling on a modestly priced, oversized beast:

That’s how my K30 came to be (K30 on the left, KPV on the right. The KPV was based on K30 molds, so it is very interesting to see the similarities…)

I will detail the build of the engine on my other thread, since it is more relevant to my Swiss Hutless. The intent was to build the K30, drive it for a little bit, and flip it for a profit (those engines started picking up some incredible equity, eBay examples ranged from $2k to $4k!)

What I ended up with was a direct drive K30 with a 27mm IBEA Yellow Power carb, on an old-ish Margay Brava with some very neat bodywork.

…And also a by now KartPulse-famous, really special axle…

The axle was manufactured by a company called Fiber Dynamics, which was involved with the then defunct US-F1 project. It was a neat find, but the performance wasn’t there and I was constantly freaking out about it splintering on me.

Then, destiny came knocking again, changing my plans. On my first open practice day, I drove this darn thing…

…And just like that, the vintage kart bug bit me hard. It turned my hobby upside down. What I thought I liked about motorsports no longer attracted me. I was forever committed to the sport. Karting or nothing.

Got home and immediately put the Margay for sale. Within a week it was sold to a very cool guy in Indiana, who came to pick it up in a 3-series coupe…

Unfortunately, that also spelled the end of my Open KPV affair. Needing the money to fund the '80 Swiss Hutless project, I ended up selling the motor for a generous profit (!) on eBay.

The story continues, this time in my 1980 Swiss Hutless project thread :brap: It gets a lot better from here. I promise.

Thank you for reading!

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I used to autocross for about five years. Once I started competition karting, I never had the interest to do it again. You just get so much more seat time at a sprint track that it’s ridiculous.

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