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.

 

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

 

 

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

 

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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.

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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.

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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.

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Next was the triple tree for the steering.

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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.

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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.

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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.

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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.

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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.

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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 Gopowersports.com. 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.

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With the torque converter, it can now do wheelies.

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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.

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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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