Odd Engine Conversions

I live in the Netherlands and we have 50cc moped races.

The bikes like above are build to race in those classes.

Its mostly 125 and 85 frames with the engines removed and put in 50cc engines from mopeds like Derbi or AM6 engines.

It is a very competitive class. Mostly because you need to know how to build an engine. A couple friends race kx125's with 50cc moped engines and need to rebuild the engine every 2 races.

I would love to ride it. I don't know that it would be my ideal bike if I had just one bike in the garage.
As with many Italian things, it is made with style and passion!

There was a fad in the 80s where ISDE riders would compete on KDXs with 80cc engines

Not a 'Fad'.

It was a serious Class.

Larry Roeseler did an ISDE ( maybe 2?) on a KX 125 / 80 conversion, to fit into Team requirements. A KDX chassis would have been Tank like.

There were quite a few brands that made full bikes, with theirs or others engines. Same with 50s - you can find 50 racing videos on YouTube.

And, they were absolute weapons of things.

I was lucky enough to have a course checking / secret check job at the 92 ISDE. I'd ride the parts of the course each day, at the same time as the 80s came through. Following those blokes was an education in total riding commitment - by them. Well, I had to do the same, to keep up with them / not get in their way. They were Pinned at all times, and, as only around 5 / 8 of them came over, they were the very best of the class. I had my CR/XR hybrid that I was pretty bloody competent on, but they were something to see, flat out through stuff they had never seen (well, their course checkers had......), most days.

I had enormous fun riding and hanging out with them. Only an Italian / European could ride utterly flat strap all day, with a silk scarf around their neck, and get off the bike after 6 to 8 hours riding, and look totally fresh. Then go over and chat up the nearest good looking females..............

Man, I'd love to ride a small motor in a full size frame. Seems like it would be so much fun!!

I was lucky enough to race Langtown back in it's heyday on a KX 80 Big Wheel with an XR200 motor, talk about fun!!

Personnally I like it. It is not for every tracks but I think it can be fun on old school ones (slower and with more bawl turns, without huge jumps, and hard pack / not ripped). A highly mod 50cc can deliver almost or as much power as a stock 85, so it is not super slow either as most people can think initially.

For instance as a kid/teen, I hated 50cc scooters, thinking it was slow and a bit ridiculous; until I had one later (yamaha aerox with 70cc alu with single ring piston, 25mm carb, similar engine to the european championship), which I progressively prepared until being faster than a golf gti on the 0-60 (on dyno, and in real). I even overtook a 600gsxr in a roundabout and a 800 bmw in a relatively fast uphill mountain road. It was making 140km/h (87mph), 130km/h uphill, and 115km/h in wheelings.

I also heard the mobcross class was fun and competitive as others in this thread have mentioned. If we could compare that conversion to what it is currently produced, ready to go, there is 1 bike a bit like that which i guess would be super fun to have on certain tracks :

http://shop.tomoffroad.com/tm-racing/4434-mx-85-1921-2020.html



https://www.youtube.com/watch?v=f071yx2pKMA&ab_channel=LorenoRace

https://www.youtube.com/watch?v=YVarLuiVLZE&ab_channel=YannickvanderVegt

Wow, with a cvt too?

They definitely got their monies worth out of that rear sprocket.

I got the chance to spin some laps in a rm125 frame with a sx85 engine in it. If actually felt fast but it was hard pack.

This is a dutch bike.
It is a yz125 with an am6 50cc engine.

I think you will find more info by searching "mobcross". That may not bring to what you want exactly but it is the term used in france for 50cc (or 70cc) that are modified to race on a track, usually a track specifically designed for that. I think it is more a north and possibly north west thing as I never saw one. Also, if I am correct, there is also a 50cc enduro championship that takes place during the normal enduro championship. It must be very tough as it is pretty extreme, lots of good french riders in this disciplin so the events are tough even for bigger bikes.

Here are 2 pics from modded mobcross then what we see on the road very often (hm, sherco, beta), including 1 a bit modified. It is quite popular as you can ride it on the road from 14 years old (you have to wait 16 to pass the 125 driving licence, and 18 for the car)

oh, and btw, there are kit up to 94cc, with 34 carb, and some hits now 100mph thanks to the 6th gear

My dad used to put kdx200 engines into kx125 chassis. I believe he made several of these.
I had a 2012 150xc with a 200 top and bottom end.

About ten years ago I saw a lot of xr100 motors stuffed into cr80’s

They need a turn-key instal kit for the blown up 250f market. I'd buy one...

The only comment to make any sense in this whole thread.

250f frames are to heavy for 50cc engines.


In the picture is a friend that rides at a local race on a yz85 frame with an 50cc moped engine with a CVT.
The blonde guy in the background is Mark Tielemans who was first in the Dakar rally in the malle moto class until he crashed on the 2nd to last day.

We put a KDX 200 engine in a KX 125 frame. Other than the trans, it's a great bike. I have also put a few 200sx engines in modern frames. The best one was an 03 200sx engine in a 2013 150sx chassis. Super fun bike.



The 2000 KX 125 engine is for sale, lol...

Moto Armory.

Frankenbikes are very common in the pitbike world. The hot setup now seems to be taking a CRF150r motocross bike and installing a modified XR100 engine in it. Apparently it's really easy to find small bore 4 stroke motocross bikes with blown engines! LOL

It's way more fun riding a slow bike fast than a fast bike slow.

Saw this on Marketplace. Cr500 with an XR350 engine shoehorned in.