Motorized bike build

By diyauto

13 minute read

( 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.


2 years since I’ve messed with this thing. Getting married and buying/renovating a house will do that. Now that the state is on lockdown for 3 weeks I’ll have some time to work on it. Hopefully I’ll have it cruising around before lockdown is over, would be nice to cruise in when it warms up a little.

So one of the main issues is the chain hitting the engine mount and bike frame. I have another idler pulley so either moving the one to the bottom part of the frame or adding the second idler. Hopefully we can route it in a way that it’s not contacting anything. It’s close too so it’s a balancing act.

Also have to install the throttle and finish doing the brake line. So I’ll have to get those sorted. Also hooking up the fuel and electrics.

But first things first, got to find the box of parts and hope everything survived the move.

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Well I found the box of parts! Everything appears to be relatively intact. Time to get started.

Moved the idler to the bottom section of the frame. I also trimmed the engine mount and had to file down the rear brake bracket screw. It is still pretty close to things but hopefully will be alright. I’m sure I’ll have to adjust it more.

Put the clutch back together and ran the cable. Thankfully I had a screw in my screw drawer that fit the clutch arm.

Harry is helping by inspecting the line.

Had to drill a hole in the handlebar for the throttle assembly. It came together pretty well.

The carb was a little tougher. This is the performance carb and operates a bit differently than the standard one, the throttle cable doesn’t interact with the needle/jet at all. Thankfully I looked up the instructions as you have to throw out the metal tube that the cable snakes thru or it won’t be long enough. Also you need to use pipe sealing tape to hold the remaining nut section in the carb assembly. If it falls out apparently your throttle can get stuck. Not great!

Wiring is pretty simple as expected. It doesn’t look great now but I’ll dress it up later on. Just want everything to function first.

Fuel system was easy. Just a tube. It was nice that they included a fuel shutoff valve.

That’s it! Just have to check the garage to see if I got enough gas and the right kind of oil to mix in. Hopefully will be driving this today!

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So I had my first ride yesterday, it was glorious but short lived.

Filled up the tank with gas and 2stroke oil. Tried several times and the bike wouldn’t start. Figured it was an electrical issue. Tested the components and they seemed fine. Opened the side of the motor and noticed the magneto wasn’t spinning when it should’ve been. That will cause a problem.

The clutch was out of adjustment so the motor wasn’t actually spinning. Adjusted the clutch and I was off!

The bike drove great, took a few tries for it to start but it was soon up and running. Took it about 3/4 of the way around the block when there was a loud bang and the rear tire locked up. Had to half carry the bike home.

This isn’t good. 

Neither is this.

All the engine mount nuts had vibrated themselves loose which caused the engine to shift and messed up the chain, at least that’s how I think it went. Not a huge deal, I replaced the super long front mount rods with the stock ones, and added a locking nut to each one so they are doubled up. It seems like the chain is a lot more loose now so I’ll have to tighten it up some. Hopefully will be back on the saddle today.

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Finally have it up and running! It took a bit of fiddling to get there. I checked if I could remove a couple chain links, although it seems like a decent amount of slack I had no room to remove any links. I readjusted the idler and added a second one to keep the chain from slapping around. It took some adjustment to keep the chain from hitting various parts but it seemed to work.

I did notice while riding at a constant speed the engine noise would go up and down at a rate of about 2 Hz, in time with the idler pulley bouncing up and down almost like it was bogging. Could be due to a resonance related to the stiffness of the pulley spring, I’ll try swapping it out with a stiffer spring at some point.

It was quite fun to ride, although I was worried about something breaking so I stayed in the subdivision. A couple items to note/improvements to be made:

Even with the softer mounts the bike vibrates quite a bit, especially at higher speeds/full throttle the whole bike is buzzing. After a long stint of riding my hands were tingly. I’ll probably wear gloves from now on, especially during long rides.

It takes a couple tries to get the motor started, don’t know if it’s because it’s a brand new motor or what.

There’s a decent amount of resistance even with the clutch fully in, maybe because of the two idler wheels. Will have to investigate. This makes the multiple starting attempts a pain as I have to get the bike up to speed.

The clutch handle that comes with the kit is pretty jankey, the handle has a lot of play and is cheaply made in general. With its placement I can operate it and the front brake with one hand, but I’ll eventually upgrade to a better handle.

The brakes are pretty decent, the rear is sort of weak but in combination with the front disk the bike stops well.

The kickstand is inadequate with all the additional weight, unless it’s perfectly positioned the bike falls down, will have to look up alternatives.

The seat doesn’t have a ton of cushion and hurt after a while. It looks cool but I’d want to swap it out for longer rides.

The bike looks pretty cool even though the paint is getting worn from all the assembly and disassembly. All the neighbors walking around smiled and waved.

Going to keep riding and improving it. One of my coworkers just built an electric bike from components he found online, we will do a race at some point in the future. :D

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