In reply to fanfoy:
Yeah, that's one of my options. If I go that route, I'm going to have to modify the frame even more, as there's nowhere to put the shaft right now.
In reply to fanfoy:
Yeah, that's one of my options. If I go that route, I'm going to have to modify the frame even more, as there's nowhere to put the shaft right now.
So, since I picked up my mess of a project, a friend picked up a 1970 Rupp, which are basically the Ducati of minibikes. That caused another friend, Greg (known as Pseudosport on here), to impulse buy a 1971 Rupp Enduro frame on eBay from some guy in CT. So, today, I went with Greg to grab the frame. What we didn't know is the seller was basically the emperor of all things minibike, especially when it comes to Rupp bikes. Here's a small sampling of what this guy had:
The guy had 30+ bikes. These were the "project" bikes. 
He also had a cache of NOS parts and inventory like you would not believe. Greg picked up this guy:
After getting back from that trip, we focused our attention on mine. I left off with talking about a 5.5hp "Craftsman" engine I had kicking around. It wouldn't fit with the stock gas tank, so it was removed in favor of a top tank that my nephew sold me. After removing some shielding and trim, I was able to get the engine on the frame, and it actually fit well!
And remember the chain issues? Well, that's not a problem anymore. Everything fits as it should now.
The new "idler" I bought actually moved the chain too far over and was messing with the alignment, so on went the old idler gear, which actually works now. I moved it up to cut the slack a bit, and it works as it should now.
And yes, it runs!!!
Next steps are mounting the throttle, fixing the brake, mounting the seat and tank, and then make it pretty.
Neat project. Pretty sure that is a Kawasaki KV75 front wheel. It may also be a KV75 rear swingarm. I have two of those KV75s. One used to be my pitbike when I raced karts. Since it was a two stroke, I used to run the pitbike on methanol, castor oil and 5% nitromethane. Becuase I could :)
This was so long ago I feel nostalgic. I miss racing.
Update time!
With the Gp Du Lac Chargoggetcetera 24 Hours of Lemons event in two weeks, I need to get this POS up to snuff so I'm not pedaling around on my high school mountain bike all day. With that said, I brought the minibike to a friend's place yesterday where we were prepping the race car for the event, and it served as a great distraction to getting real work done.
I wanted to get two things done to the bike: mount the gas tank and mount something to sit on. The tank was easy: I just drilled out some small steel plates and sandwiched the tank between the plates and the frame. The seat, on the other hand, was much more of a challenge.
Since this bike had once been a chopper, the seat mount was long gone. The seller gave me a "seat" with the deal, which I just realized was the sissy bar backrest. That wasn't going to work. But what was I going to use?
In a coincidence of sheer laziness, I had this little garden cart in the bed of my truck that had been sitting in there for about a month now. I was going to scrap it because it was getting rusty, but I hadn't gotten around to it yet.
And then, a sawzall appeared.
Then, a wild MIG welder suddenly appeared!
And BAM! Tractor seat!
I cut up the garden cart and pulled the seat out with it's mount. These things are on a giant screw/swivel for height adjustability, so we welded that mount to where the seat frame used to go. It still swivels up and down, and is height adjustable! I need to get some sort of lock nut to keep it from swiveling around while riding, but I fit better than any adult should on this stupid thing.
After that, my friend came out of his garage with a surprise. This front plate was salvaged from an old REO motorized reel mower, and it nearly fits the front fork area. It was meant to be.
I now call it the REO ButtWagon. 
Next on the agenda: making the brakes and throttle work. Stay tuned!
Tony Sestito wrote: I now call it the REO ButtWagon.
There couldn't be a better name for a LeMons pit bike. 
The fork is bent from ramming something. If you straighten it steering will be less twitchy and you'll have more room for your feet so the tire doesn't hit them. My friends and I all had mini bikes & go Karts when we were kids in the late 60's early 70's before moving up to dirt bikes & cars. I was the neighborhood "go to" guy to fix them
NOT A TA wrote: The fork is bent from ramming something. If you straighten it steering will be less twitchy and you'll have more room for your feet so the tire doesn't hit them. My friends and I all had mini bikes & go Karts when we were kids in the late 60's early 70's before moving up to dirt bikes & cars. I was the neighborhood "go to" guy to fix them
Yeah, it's bent but it doesn't seem too bad to ride. I think they bent it on purpose to fit the bigger wheel up front. Or, they smacked it into a brick wall. 
With the seat set back as far as it is, it's actually not bad as far as riding position and foot room goes.
I still wish I had my old go kart and mini bike. The mini bike I had was especially cool. It was all green with a green metal flake seat and a working headlight. I think I gave the thing away after I got a car. I'm definitely having fun with this one this time around.
A little more progress...
Last night, I started installing the twist throttle. Things got... well... complicated.
While mounting the throttle to the handlebar was easy, connecting the cable to the carb was not. I didn't realize that the engine, a Tecumseh OHV 5.5hp unit from a Craftsman snowblower, still had it's snowblower throttle assembly fully intact. Usually when you take the airbox off of these types of engines, it disables all that stuff. Stupid me.
ANYWAY...
I was trying to figure out how it all works, and how I could retain the engine governor and use what's there to make it so I don't blow the thing up.
That lever has three detents: off (which engages the built-in kill switch), a middle setting that disengages the switch, and a full-on setting which opens the throttle blade all the way via springs connected to the governor arm that's connected to the throttle body. The goal here is to use that throttle arm to connect the throttle cable, and have it actuate it with the twist grip.
Here's a view of the governor arm. It's adjustable via that nut on the bottom, and there are different holes for tension changes.
I was able to disable the detents by prying the arm assembly back from the rest of the assembly, and I'm going to lube it so it moves more freely. Then, I need to change the tension on the governor arm and install a return spring. I'm hoping to have this buttoned up by the weekend.
I know you already have the chain alignment and such under control, but what possibility is there for running a larger rear tire? Should help that thing be less of an instrument of death-by-wheelie.
This is a fun little build. Looks like I just found my next project...
In reply to 4cylndrfury:
Yeah, that's something I'd love to do. Whether it's just putting a larger diameter tire on the wheel, or swapping out the whole thing altogether, that would be a nice upgrade. Right now, the sprocket comes dangerously close to the ground.
Another update: no pics this time, with some good and some bad.
I brought the bike to Pseudosport's place yesterday to try and iron out a few problems, mainly the throttle and the brake setup. After some finagling, we were able to get the throttle cable to attach to the existing throttle assembly. It's not the smoothest engagement, and my $8 Amazon twist grip throttle isn't great, but it works! The brake, while MUCH better than it was, still doesn't want to stop too much.
The other problem is that the engine doesn't like running as much as it used to for some reason. While we could get it to fire up, it was chugging with the bike on the ground. That leads me to suspect that the clutch is too tight. To add insult to injury, the pull cord frayed and I need to pull it all apart to fix it. Blah. 
I do have another clutch, but I'm not sure if that one is any good either, and with the event coming up next weekend that I bought the thing for, it looks like I'm likely pedaling on the ol' bicycle. I'm not giving up on it, and while I'm disappointed, it's still a lot better now than when I bought the thing a couple months ago!!!
dont lose hope
Necro-Bump! And with a change of plans!
Sometime after this thread, I kinda gave up on the Deathtrap. It didn't want to run right, and I honestly didn't have time to deal with it. I ended up giving it to my nephew who actually found the thing at the swap meet I bought it from, and he's since re-painted it and installed a 6.5hp Predator. The thing is living its best life now.
That left me without a minibike, and without one, I couldn't be part of my group of friends' minibike gang. Then, I found this thing via Facebook Marketplace last summer. Say hello to Deathtrap 2.0:
It's a "Baja Racer" branded minibike, more commonly known as a Chinese Doodlebug clone or just Doodlebug for short. These were sold in places like Tractor Supply and Walmart for a short time. I picked this one up in complete, running condition for $100. While it runs, it's saddled with a pathetic 97cc 2hp Honda clone that just doesn't cut it.
The good news is that these bikes are very popular with the minibike modding crowd, and engine swaps are well documented, the most popular of which is the Harbor Freight Predator 212cc 6.5hp engine. It sat mothballed until I was ready to grab one. A few weeks back, a friend found himself with a spare from a snowblower he cobbled together over the winter. When other stuff broke on the snowblower, he offered it to me cheap. It has only a couple hours on it, so it's practically new.
Last night, I got bored after work and pulled the 97cc off the bike to see what's needed for the swap.
With the little 97cc turd off, there's so much room for activities!
Here's both engines side by side:
As you can see, the Predator is a lot larger. The good news is that after drilling a few new mounting holes, it will fit fully dressed! I have a clutch in the mail, and once that shows up, I'll mount it up.
I'm also thinking about painting the bike a different color. I already have a ton of silver metallic paint on the shelf, so maybe it will end up that color. Either that, or some hue of blue close to my Power Wagon.
You don't get off that easy.
We need pictures of DT 1, even if it isn't yours. lol
I'm just gonna leave this here https://www.amazon.com/Lifan-125cc-Engine-125M-B-EN18-BASIC/dp/B004S3QSYW
you may be able to find them cheaper on fleebay
*edit https://www.ebay.com/itm/LIFAN-125CC-Motor-Engine-XR50-CRF50-CRF70-COOLSTER-4-UP-PIT-DIRT-BIKE-I-EN18-SET-/370100597963 With wires and carb
8hp with a transmission, should be able to go ludacris speed with that and the price really isnt too bad, considering you have a trans.
I'm kinda doing mental aerobics on building a pitkart around a cooler with the 125cc Lifan shifter.
In reply to Apexcarver :
From what I'm reading, this bike with the 212cc Predator should be capable of about 40-45MPH, maybe a little more. I think that's more than enough!
noddaz said:You don't get off that easy.
We need pictures of DT 1, even if it isn't yours. lol
Ask and you shall receive.
He's since taken it apart again for paint. It's now gray with a red seat. But it does run and it really rips! He says it could use a new clutch, though.
Digging this
Over the weekend, I went to a bachelor party up in Maine with a bunch of friends who all have minibikes, and everyone that had one was bringing theirs. Since I figured we'd probably get bored at some point, I brought all the pieces to mine to see if we could slap it together.
Here's my friend Greg making a drill template out of cardboard. We had to drill 3 holes in the engine mounting plate to mount the Predator. After we got it all lined up, we just had to shorten the chain and attach the throttle.
And OH MAN DOES IT MOVE.
I made it up this hill in less than 10 seconds. You have to lean forward and dig in to stay on it!
It's also DANGEROUS AS HELL. It bit me almost immediately; After firing it up for the first time, it ended up jumping a bit and bashed my hand off the rear grab handle. Then, Greg tried giving it a ride, and it pulled the front wheel and tossed him off on the pavement. It also tried tossing me again after that, as well as a few others.
After that, we christened the bike "Road Rash". And yes, I'm totally getting Road Rash stickers for it.
After everyone else with their bikes showed up, we had a blast! It felt like we were all 10 again. And now, I'm in a minibike gang.
The three other bikes are all vintage Rupp bikes that are about 50 years old. Mine was the only one without any sort of suspension, but on pavement with its smaller tires and 6.5hp, the thing is a rocket and it roasts the others. Once it gets above 30mph, the whole thing starts shaking and rattling your brain, so I'll have to address that.
Late in day 2 of the bachelor party, it started making some bad sounds. It would start fine, and then make an ungodly screeching sound and stall. I noticed that the clutch bolt kept coming out, but even after tightening it, the same thing happened. I'm wondering if the clutch itself is bad, so I'll be testing the engine with the clutch off to see if the same thing happens.
Even with the failure, it's still a blast.
I'm glad you revived this thread. I missed it the first time.
I hope you’re watching these guys, they’re great!
https://m.youtube.com/user/CarsandCameras
My inspiration for buying two go karts, a DR125 and now my son grew up and bought himself a KX125 while I still love the Karts.
One was $80 and one was free. Bought a new 212 for the first And was able to unstick the piston in the other and bought a new $10 carb.
So much fun and the neighbors get a kick out of me driving them more than my kids do. Hell, my wife can drift the things across the backyard now.
Bumping this one back up.
Last weekend, I was waking up all my small engine-equipped things, and decided to see if I could replicate the bad sounds the minibike was making last year. I had no problem doing that!
Again, I'm thinking clutch. The engine runs too well for it to be something internal. The oil looks fine, too. I lubed the clutch bushing a ton, but that didn't help.
"Do not exceed 150 pounds"
Love that sticker. Anyway, I'd bet on clutch too. That sounds bad. Swap it out.
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