Building A Mini-Bike

I got my hands on a run down Baja Doodlebug mini-bike in 2014, which I decided to fix-up.

I bought a Harbor Freight Predator 6.5hp engine and modified the engine mounting plate on the Doodlebug. This increased the performance of the mini-bike enormously, allowing me to ride it. After riding it like that for awhile, I decided to modify the engine with a high-flow air filter upgrade, larger jet for the carb, and an exhaust pipe. This increased the top speed of the mini-bike to 35 mph, which was getting a little too fast for riding on the gravel we have out here in the country.


Doodlebug after I got the Predator 6.5 hp engine on it.



Doodlebug with modded engine, paint job, and other new components.




Well, after experiencing the fun of the Doodlebug, I decided to build another, frame and all. So in October (2015) I got to work on it.

First I started building around the rear tire and wheel, which I had bought a few months earlier at BMI Karts.


From there I started welding the frame, and as I don’t have a tubing or pipe bender yet, I just left the pipe straight which I think turned out all right. It should be mentioned here that the frame is welded from black iron pipe, which I got from Lowes.


The welder in the background is my Hobart Handler 190. It is an awesome MIG welder and my welding skills do not do it justice.

From here it was a matter of welding and grinding to get a serviceable frame. Leaving the pipe straight caused a few problems that could have been avoided if I had bent it.


Next was the triple tree for the steering.


This part was a little sketchy the way I did it. I should have bought a 7/8″ hole saw to drill holes into the flat stock and slip the forks through those. But instead I welded the forks onto the underside of the triple tree, which made it very weak.

I had a 20″ bicycle wheel, from a little girls bicycle, that I based the forks on.


After that, I stole the engine from the Doodlebug and did a mock up. Also, set up the brake, and welded on an engine mount.


On to the handle bars. You can see the Doodlebug in the background in this pic. I also welded the kickstand from the bicycle on the bottom of the frame.


After that, I got some foot pegs welded on, a seat cut out of OSB, a jerry-rigged gas tank, the throttle, and the brake hooked up.



After taking some test rides, the welds on the forks cracked. Which was not good.

So, I ended up welding pieces of angle iron to the forks to make it sturdier.


After that, I test rode it a few more times and decided that it need a torque converter (Had been using a centrifugal clutch). So I found one and ordered it offline, from While installing it, I found that they hadn’t sent the correct bolts to mount it to the Predator engine, so I had to make a run to Tractor supply.


With the torque converter, it can now do wheelies.


After that, I decided that it was time for a seat. I had some fake leather and foam leftover from making the doodlebug a seat, so I just applied that to the OSB seat I already had.







Blurry pic, but you get the idea.


Now it needs to be torn down and painted, but that probably won’t be until sometime next year.

I think it has turned out nice so far, and I learned a lot by building this bike. It didn’t turn out as much a mini-bike, more like a medium-bike. I’ll probably do more bikes in the future, using the lessons I learned on this one to make them better.

What do ya’ll think? Leave a comment below if you like it.

Thanks for reading,

Alex T.

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