for my birthday i got myself a bicycle motorization kit off ebay,

i worked on plenty of bicycles but never played with an engine, getting the hang of riding the thing should be interesting.

here i will share the bits that were not included in the stock instructions. or needed renegotiation.

my efforts have been keeping the boy next door entertained, not sure that his parents appreciate the plumes of blue smoke but they are too polite to say.

the engines shipping weight is 11kg with about 3.5hp I wanted to keep the power to weight ratio in the right direction. . You don't see many beach cruiser frames in South east London .They look really heavy.

my preferred frame size is about 18 inches. my doner bike is a fairly decent 19 inch aluminium specialised. the frame weighs about the same as a narrow wall cromo steel frame. thin wall steel frames crush easily. The engine fit inside.

The euro coaster breaks have a chunky hub.the chinise ones have a normal size one that fits the kit rag joint and weigh considerably less.

Most breaking will be done with the front I went from cable disk to hydraulic to save more weight and get better stopping.

I went from trendy red tyres to branded skinny tyres that take more pressure to reduce rolling resistance.

The forks are some old dirty suntour somethings. I removed the elastomer from within the spring to increase travel.reduce preloaded. and it's another few grams going into the parts box.

changed the front chain ring from a 42 or 44 triple to a 46 sturdy aluminium fixie type one.

[Play Video]

• angle grinder bench grinder and file
• impact driver with 10mm socket
• spanners and screwdrivers
• scissors
• knife
• spanners
• hammer
• drill

• 80cc motorized bicycle kit
• coaster break hub, spokes and rim. £11 £0 £10
• doner bike £63
• thick grease and wd40
• fully synthetic 2 stroke motor oil £13
• nuts bolts
• car exhaust pipe clamp
• thread lock
• lots of zip ties £6
• replacement chain tensioner air filter hand grips and plug. £9 £3 £5 £6
• break cable adjuster screw
petrol £2.50

total cost approximately £195.50

Step 1: Front Mounting Engine

used the supplied plate with wonky holes , i used a car exhaust pipe clamp to fit around the frame. i used threadlock on the bolts.

thinking about it i use thread-lock on just about everything. you should too :-)

having a 2 leg kickstand makes building and maintenance much easier. Tho using the pedal to start it on the stand can bend the stand. I start it by grabbing the wheel.

Step 2: Rear Mount for Engine

the stock fittings almost fit, the radius of the solid portion of the clamp needed increasing., bench grinder angle grinder hacksaw nail file take your pick.

i also had to take a bit off the plate section because it was catching the chain.

Step 3: Fitting the Twist Throttle,

• its supposed to have a tab on the inside that fits into a hole you drill in the bar, this tab was thankfully missing,
• once the throttle was fitted i drilled through it in a section that contained on inner parts into the bar, i then. put a screw in the hole.
• the stock grips looked horrible and are uncomfortable, with some effort and a greasy spoke i removed it and put something better on, had to be careful not to damage the throttle as it is poorly made , as a safety feature i added a clamp on the end of the bar in-case the twist grip falls to bits.

Step 4: Clutch Cable

  • the clutch lever is well made and easy to fit, as the cable has no special nub thing at the engine end so shortening it to fit the frame is easy.
  • the cable at the engine end has two springs a big one that acts as a barrier between the hot engine and the plastic cable casing, a small spring that goes around the exposed inner cable to make the clutch action springier.
  • the cable end sticks out in a inconvenient stabby leg place , a small zip tie makes it behave.

Step 5: Chain Alignment

as my frame is disc break specific , i wanted a coaster break (thoroughly not recommended by anybody for motorised bicycle) iv never ridden a coaster break ,they are not so common in the uk, having a coaster means no extra lever on the bars and no gear levers and cables to think about, keeping things tidy and saving a tiny bit of weight, the coaster arm is bolted to the disk break mount.

the coaster hub is narrow and the frame is wide, and having a big chaining on the front exacerbates the issue. the wheel is a 32 spoke , the motors bolt on sprocket is designed for 36 spoke wheels,attaching the sprocket to the wheel despite the wrong spoke alignment wasn't two difficult ,tho i did snap a couple of bolts, i needed to true the wheel a little bit after attaching the sprocket to the freshly built wheel (first wheel iv ever built)

the supplied chain tensioner is a unsprung barely adjustable horrible thing that self un adjusts, the nature of the sprockets of the kit make the chain tension variable , it can be taught in one position then turn it round and its very loose. im replacing it with a motorbike sprung one. That was cheap and of questionable quality. by combining parts and adding a spring with decent springiness.


the chain has a splittable link , if the chain needs shortening grind off a bobble and punch the pin through with a hammer and nail. motorbike chain splitters are expensive if you only use it once.

Step 6: Fancy Sparkplug.

the instructions have some recommendations for replacement plugs , looking at some internet chatter i got what seems to be the best one for it, its made from iridium (whatever that is) it requires a bigger spanner to fit it.

Step 7: Semi Waterproof Electrics

i skipped the silly wire clips, that connect the kill switch, magna dynamo thing and the spark generator box, soldered the wires together the applied heat shrink. the kill switch had a very long wire so i shortened it.

Step 8: Get the Carburettor the Right Way Up.

• i learnt this the hard way.
• its a 19 inch frame the carb fits nice upside down or on its side but it wont work.!
• what way up does a carb belong?
• the big round cup shaped bit that is not an air filter goes at the bottom. it fills with fuel, and there's a floaty thing inside that shuts off the fuel when it reaches the top, of if its upside down starting is difficult as the fuel is shut off.
• making the carb fit the right way up was tricky, the engine runs it its at a 45 degree angle , but not brilliantly, when its properly upright everything is much better , its well worth the effort detailed in the next couple of steps.

Step 9: Air Filter Adjustment

as im waiting for a nice looking filter from ebay i modified the stock filter so it will clear the frame. chopping bits off with an angle grinder and trimming with a sharp knife, clean off any bits of plastic before putting anywhere near the carb or engine, molten plastic will not lubricate your engine or carb.

Step 10: Happy Accident

• i originally got the engine running with the throttle cable passing the right side of the top tube,
• with a little running the engine settled on its mounts ,it seems to want to sit with the cylinder head not central to the top tube it sits a bit to the left, its just enough to mount the carb almost upright with the throttle cable to the left of the top tube,
• by adding a break adjuster screw with the thread ground off to the twist grip throttle outlet, it was one with the cable slot down the side ( the throttle cable has a nub at each end so cannot be unthreaded as far as im aware)
• by shortening the adjuster and removing the lock nut from the top of the carb it can be rotate so its almost upright.
• make sure there is a good seal between the carb and the tube out the engine to which it attaches ,air leaks make 2 stroke engines run badly.

Step 11: I Never Noticed

inside the carb where the cable attaches the clip on washer can be attached to the pin in different positions , that affect the fuel air mix.rich or lean. im not sure but it may require a different nossle size to suit if its adjusted, (the nossle bit is inside the cup with the floaty bit) i tried moving the washer about and it made the engine run poorly so i put it back to factory setting.

Step 12: Fuel Filter

  • they are traditionally are fitted upright so that the fuel travels downward through them.(easy to see if there full of debris)
  • im short of space so sideways it is, note that they have an arrow on the side denoting the fuel travel direction,i could only see it after handling the filter with dirty oily hands. try to make your fuel path as down hill as possible.
  • i added metal hose clips to be safe, they also are useful for putting small zip ties through, bigger zip ties go through the smaller ones and attach tightly to the frame, so the filter ends up well secured without risking breaking the plastic.

Step 13: Mounting Fuel Tank

• the tank mount bolts are apparently easy to break, my top tube is rather chunky, i used flexible metal strapping from a builders merchants,(its used for bodging studding together and other iffy carpentry ) i also used sticky foam pads to save using excessive force on the bolts.
• the electric spark generator is zip tied to the strapping, as that is also prone to being broken with bolts.
• remember the rubber washer on the fuel cut off tap.

I wanted to mount the tank as far forward is possible do I ground off the cable mount on the top tube.

Step 14: Cable Routing

I drilled the frames cable mount so I could thread the clutch and throttle cable through. meaning less zip ties on the frame.

notes on running in

the fuel tank is about 2 liters , for the first 4 tanks , 2 liters of fuel require about 150 ml of oil note that this didnt fit into the tank in one go.mix it in a jerry can. im running it for about ten minute intervals two or three times a day. only revving up to about half way in bursts, keeping an eye out for chain tension and loose nuts. in this time the gaskets should seal properly and a bunch of other stuff will happen, im only half way through the first tank and im noticing subtle improvements.

<p>Good job with the bike, you have avoided almost all common beginner mistakes with these kits! There is one thing you may want to look into fixing right away though, and that is getting a better rear sprocket, as the ones that clamp to your spokes like that will pull the wheel out of alignment pretty quickly. Consider getting a hub or disc brake adapter such as the one I use in my <a>79cc predator motorized bicycle instructable</a>. Also I noticed you mentioned that you are getting a spring loaded tensioner, some people have issues with these as the chain should have a little bit of slack. The best course of action is to remove the chain tensioner entirely if you can, and just adjust the position of the engine to take up chain slack. It is possible as long as the chain doesn't rub against the frame. I'd also like to point out that the 80cc/3.5 hp figures you most likely got from the seller are false advertising, these engines are actually 66cc, and can manage at most around 1.5 hp without heavy modification. Now on to some advice: If you want some more power consider making a custom exhaust pipe, the stock exhaust on these engines is really crappy, you can easily increase torque by 2 or 3 times with a properly tuned exhaust pipe. Also consider porting the engine and getting a better carb. Also a word of warning if you used the stock spark plug boot, they tend to fall apart pretty quickly, and have a copper core that deteriorates easily, you can replace it with a nice carbon core one from auto parts store and get a stronger spark and not worry about it disintegrating. Oops, I appear to have written a giant wall of text again...</p>
Thanks for the input. I have not addressed the rear Cog yet. Have been playing around with exhaust system. made the red one , might make an instructable of it. While I was waiting for the banana pipe to arrive. changed the fuel tank for a narrow rear mounted one. got a better fuel line. and made a better front engine mount. now the new air filter touches to seat tube and the top tube. don't seem to have a picture of my improved chain tensioner on this phone the one of eBay had an incredibly weak spring.. <br> What's porting the engine? <br>and how would I go about changing the ht lead when it appears to be sealed into the potted coil unit?
<p>Engine porting is basically just doing a little quality control on the intake and exhaust ports. The way they come from the factory, there is often a lot of gunk and bits of metal sticking out, the holes are not smooth like they should be. This creates little eddies of air the restrict the amount of air which can be moved through them. Sometimes the ports are also not in quite the right places height-wise either. You can clean them up manually pretty easily. Do a search for engine porting on motorbicycling.com if you want more info on that. Here's a decent thread I found http://motorbicycling.com/showthread.php?t=16646. As for the spark plug lead, it is sometimes glued to the CDI, but it's not very good glue, and it just screws off, take a pliers and use it to twist the lead till it breaks the glue, then you can unscrew it and screw in a new one..</p>

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