#1
Hi,

My son received a 1971 Roadster 2 from his Grandfather a couple of years ago that he bought as a kid. It is mostly stock and been sitting in storage for more than 20 years. Changed the oil and filled the tank. After about 20min of fooling around got it running! First thing I noticed is that the original engine was tired! Also the carb kept plugging up from rust in the tank. I suppose a 50 yr old minibike you can expect things like that? The first picture I took of it was right after getting the bike running and taking it out for a ride in the middle of winter and through some snow. The purple cloth was to collect the gas leak.

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I pulled the engine off and took it to a local machinist/small engine guy in the area to have a look at it. He confirmed what I had expected. The engine needed a complete rebuild. It would not last long in it's current state. The crank looked like it had gone through a coffee grinder. The piston and shaft were very pitted, in very rough shape needed to be replaced.

While he started looking for parts to fix the engine, I took the mini bike completely apart and went on with cleaning it up. As you can see there were many layers of rust on all of the chrome. The grips were rotted out and cables needed to be replaced and I needed to do something about the gas tank because it leaked and rust would plug up the carb.

A couple of months or so later, a lot of rust remover, steel wool and elbow grease, I was able to get the bike mostly cleaned up and looking pretty good for something that is 50yrs old. I also removed the rust from the inside of the gas tank and coated the inside to fix the leaks and prevent clogging up the carb again. I also replaced the brake pads, found a tail light, bought a new gas cap that wouldn't leak and replaced the grips and foot peg covers.

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Now the hard part. It has now been a couple of years and we have not been able to find an oversized piston and ring set that is ready to go in order to machine and rebuild the engine. This has been taking way too long and my son is turning 15 and this thing is dragging on. I decided to buy a predator 212 and get this bike running so that my son can at least enjoy having a mini bike before he is off to college!

This is the part I really wanted interested folks to see how we modified the 212 so that it would work with the Roadster 2 minibike. The goal was to make sure that everything could be returned to stock and everything could be reversed so that someday when I find a piston and ring set we can put the bike back together as original as possible. The new predator engine bolted right on to the frame.

First issue was the exhaust and drive flanges. The engine shaft isn't as long as the Tecumseh and the exhaust doesn't line up the same at all. As you can see in the photo an exhaust manifold was pulled off of a riding lawnmower with a similar engine and another pipe was welded on so that the original exhaust pipe would slide into that piece and a simple bracket was made to bolt it on to the bike. It's not the prettiest looking fix but it works. He was able to get the drive flanges to line up with some spacers and provided just enough room to put it all together.

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Next issue was the Carb and filter housing. The way the intake is set up on the predator and with the slant frame the carb would not be level at all if you were to just bolt it on. A new intake manifold needed to be machined in order to fix this issue.

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Next a filter mount with a tab to hold the choke arm was 3D printed. This is the first one and it does work pretty good. I will need to find a better fit for a filter or else reprint a new one with a bigger opening to fit the standard filter kits out there. The next one would probably have a connection for the case vent house to recycle that air.

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And here it is on the bike:

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You'll notice an older red case around where the pull cord is attached. That is one pulled off an older engine. The black one that came with the engine was damaged during shipping or something. I had bought it the previous year from Harbor Freight and didn't open the box. Had no idea it was bent. I made no attempt to return as HF has a 90 day return policy.

You'll also notice that I had to make an ugly bracket to hold the belt guard in place. It's really ugly but it works. The ultimate goal is to get the other engine re-built and return the bike to more of a stock bike. The nice thing is though that my son now rides the bike and has fun. Also, I haven't clocked how fast this thing goes but I believe it went around 30 with the 4hp Tecumseh, and now I think it probably does over 40 with the predator engine. I know we can modify to make it go faster but it goes fast enough for now!

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I also wrapped the exhaust pipe to insulate some of the heat from burning up the seat. That seat is original and I have thought about buying a new one just to not tear up that one.

If you have questions or are interested in getting some of these parts made I have talked to the guy who helped me out and he is ok with me sending his contact information. Just DM me and I can get that to you.
 
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#2
Back when frames were cheap on Ebay I got one of these frames and built one but mine is not anywhere as original as yours, but it turned out to be a great running and driving minibike. I did not have an original front end but when I built mine you could get the Suzuki K1o front ends from BMI for $69 so I used one of them. Some pics from when it was close to finished. I'm really liking yours, makes me want to look for a original front end.
 

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#4
Back when frames were cheap on Ebay I got one of these frames and built one but mine is not anywhere as original as yours, but it turned out to be a great running and driving minibike. I did not have an original front end but when I built mine you could get the Suzuki K1o front ends from BMI for $69 so I used one of them. Some pics from when it was close to finished. I'm really liking yours, makes me want to look for a original front end.
I like the Suzuki K10 Motorcycle fork much better than the original fork. The Suzuki K10 has about 4.5 to 5 inches of suspension travel. The stock pogo stick Rupp fork about 3 inches of travel. Plus with a Predator 212cc the K10 is much heavier which should help to reduce the risk of unintended wheelies since even a stock Predator 212cc makes much more power than a Tecumseh HS40. I have a stage 3 Predator 212cc with billet rod and flywheel with Mukuni VM 22 and it is not little kid or newbie friendly and I will no longer be letting even adult unexperienced riders ride it after my wife's nephew wheelied my bike over on July 2nd this year. As to exhaust Robertson torque tubes makes an awesome exhaust which fits the Predator 212cc powered Rupp Roadster 2 perfectly.. Here is a picture of my Resto-mod Rupp Roadster 2. Nothing has been irreversibly changed and if a person wanted to convert the bike to original it could still be made to be completely stock again. Plus with the built Predator 212cc makes it a gps verified 50+ mile per hour bike that demands your undivided attention while riding it.
 

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#5
Gustoguy,

I agree with what you are saying. The original front suspension is not great on the Roadster 2. Also, even with out the Stage 3 modification, the predator 212 will lift the front end off the ground so you have to be careful!
 
#6
Gustoguy,

I agree with what you are saying. The original front suspension is not great on the Roadster 2. Also, even with out the Stage 3 modification, the predator 212 will lift the front end off the ground so you have to be careful!
In trying to solve the problem with unintended wheelies I am also putting on a 12 T jackshaft sprocket since the bike hits very hard off the bottom and it is almost un-ridable by novices.
 
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