Motorized bike build

By diyauto
( 3 )

Wanted to try my hand at building a motorized bike. My girlfriend has a moped and it would be fun to have something so we can both ride around. 

I found a cool vintage bike on Craigslist. It was owned by a guy who used to work at a Pontiac plant. He did the custom paint and corduroy seat. I really like the color scheme and will keep with a vintage cafe racer theme.

The bike rides nicely but the seat could use more padding. I will definitely be upgrading the brakes before riding to disk brakes. I may add a vintage style springer fork since the roads here are crap.

I ordered all my stuff from They have a ton of stuff and their website is well organized. 

For the motor I went with the Bikeberry 80cc Flying Horse stage 1 kit.  (link) This has the performance intake, muffler, and carb. 

I ordered the BBR softer motor mounts and the keg style gas tank which I think will look better than the stock tank. 

Here we go! I moved everything to the basement since it’s so cold in the garage.

Here is the motor.

The mounting stalk for the keg tank is way too long and presses on the rear tire. I am going to have to shorten it and weld to the bracket. When done it will fit snugly under the seat.

Started painting. Did a low gloss engine enamel for th engine. Gloss black for the mounting brackets. Good for some of the hardware and bolts on the engine. Doing red for the gas cap and a couple other things. Should look pretty cool.


Painted the engine and the bolts, turned out really good!

The kit came with a performance carb. 

Have the special rubber engine mounts. 

And mounted the engine on the bike, it’s looking good!

The rear tank is too long and hits the rear tire, I have to cut the stall down eventually so it fits. But the stock tank doesn’t look as bad as I thought. Gave it a quick paint job and painted the cap red.

The performance muffler isn’t fitting either so I added the stock one which looks better, this thing should have plenty of performance for what it is.


Ordered a heavy duty springer fork with disk brake adaptor so have to pull the old fork out.

These bearings have to be like 50 years old so I got new ones with new grease.

The stalk is about an inch too long so I cut it down.

Also ran into a problem with the rear sprocket, the inner hole is too small to clear the hub. Thankfully my work has a mini machine shop.

It’s not a well equipped shop so I couldn’t just drill out the hole in one go but it’s better than a dremel.

Next roadblock, the front hub won’t accept the disk, so I’ll either have to replace the hub or get a new wheel.


It looks like there is still more to bore out of the drive gear before it clears the hub. There is a chance I’ll get a new wheel at some point but I’m going to make it work as it is. It was too late in the evening to start grinding away at it so I’m saving that for later.

As for the front wheel, I went with an upgrade to a much stronger wheel and tire combo at the advice of the bike shop guy. With the roads being as they are I don’t want to take any chances. The disc screwed right on.

I put the front fork together with the caliper mounting bracket. It comes with some lock washers to keep it together. There aren’t really any  instructions which seems odd for something important like brakes.

Here is the caliper, it bolts right up to the bracket. Clearance and position seem good.

Got it all mounted up. It’s really looking good! Installed the clutch lever and line. The line is really long, I’ll have to get a shorter one at some point.

I lost the screw that holds the line so I’m momentarily stuck.

The front is really looking good. I found a cool looking light that I’ll buy when further along. I want to get different handlebar covers than the ones in the kit. 

Shouldn’t be too long until it’s operational!


Got the gear bored out some more so it clears the hub so the back wheel is all sorted now.

Installed the gas tank and the little intake booster. It is supposed to smooth out idle, throttle, and make it a little peppier. It basically adds intake volume. 

According to Bikeberry:

“As the engine draws fuel and air in through the carburetor on the intake cycle, the spark plug fires this mixture forcing the piston down and forcing a small amount of leftover air/fuel back into the the carburetor. As the air and fuel mix is forced back through the carburetor and intake manifold, it causes a double rich mixture which can result in a rough idle and hesitation. Primarily, the leftover air/fuel mixture, already burnt from the previous cycle which provides little or no oxygen, is cycled back to the next intake cycle resulting in bogging/ sluggish throttle response.

To take advantage of the leftover air/fuel mixture, the Boost Bottle kit provides storage for this "pre-atomized air/fuel mixture" or the leftover air/fuel mixture, leaving the intake cycle fresh and unburnt. As the piston makes it next cycle and draws a new fuel and air supply into the cylinder, the "pre-atomized air/fuel mixture" that is stored in the bottle returns to the engine as a burst, forcing the atomized fuel into the engine. In result, the boost bottle provides a "boost"or supercharge effect in engine performance.

This boost bottle works best at lower and mid-range rpm and when you are on & off the throttle. The advantage is that it brings up the horsepower and torque in the bottom of the rpm range, to mid-way through the power band (eliminating bogging).“

I’m going to replace the white zip ties with red ones which may look better, or I’ll go with black.

So far it’s looking pretty sick. It is nice to sit on it and get a feel for what it’s going to look like. 

All that’s left is getting the throttle, brake, and clutch cables the right length and hooked up, size and attach the chains, install the ignition and fuel lines, handlebar grips, probably a new rear tire and I should be ready to ride.


Put the chain on the bike part and took it for a shakedown run under human power. Had to tighten and straighten up the front fork but it worked great absorbing the bumps. The pedal kept hitting the exhaust so I bolted the performance exhaust back on. The springer fork moved the wheel forward enough that it no longer interferes with the exhaust.

Started working on adding the motor driven chain. The kit comes with a spring loaded tensioner which I installed. 

The chain rubs in a few places. On the engine mount which I can swap the plate out for a smaller one. It also rubs on the lower arm. I’ll see what I can do about that. The kit came with an idler wheel, I’ll install that and see if it helps at all.

Lots of little things rubbing or hitting. That’s what happens with a universal kit, especially when it’s going on an older bike.

Days are getting shorter, hope to have it running before winter.