A warning to those looking to mod their motorized bicycles:

Most, if not all, of the hacks and mods featured on this site were made by individual hobbyists. If you are new to working with 2-stroke bicycle engines, please by aware that there's a possibility that a mod featured on this site could seriously damage your engine. Please don't try any mod from this or any other site unless you fully understand what you are doing. The owner of this blog will not be held responsible for both material and bodily damage caused by performing a modification featured on this blog. Also remember that opening up your engine may void your warranty!

Saturday, November 26, 2011

Spring-loaded tensioner for $3

This tensioner mod is one of the most elegant I've ever seen!  Simple enough, and I believe this is the only one I've seen that doesn't rely on more than one point on the bike frame.  This is the kind of tensioner that should come with the kits.

Wednesday, November 9, 2011

Flexi-pipe muffler extension

If you want to extend your stock muffler(or any muffler) to behind your bike without too much expense or welding, that looks like one way to do it!  The post doesn't contain any details as to how exactly it was constructed or how leaks are sealed, though.

UPDATE: The original photo was lost so I replaced it with another one that uses flex tube to have an extended muffler.  Hopefully this will at least help to illustrate the idea behind the original hack.  You can learn more about the muffler extension seen in the photo in this thread.

Friday, November 4, 2011

Break-in secrets

This article on the Mototune USA website describes a somewhat controversial method of breaking in a new engine.  The manuals for our engines always tell us to start out with heavy oil(16:1) and break it in easy.  This idea is increasingly becoming mythical as many people seem to have better results breaking in an engine by using less oil and using less oil.  According to the writer, the most important period in the break-in period is the first 20 miles, and if it's not done right, the piston rings may not seal to their full potential.  I'm assuming I understand this correctly.

Read more about breaking in a new engine "properly"!

Make your 2-stroke sound like a Harley

Hondabicycle from motorbicycling.com claims to have an exhaust mod that will make your 2-stroke engine more like a Harley.  I'm pretty skeptical, but it's a fairly inexpensive mod.  It involves creating an muffler end cap with two baffles and exit holes.  The muffler is also packed with fiberglass.  If anything, this will at least quiet down your bike if it's loud.

This mod could probably be achieved more easily in combination with my washer end cap mod.  Since that has been proven to be an easy and superior end-cap, you could drill two holes in the washer and make your own baffle tubes.  Then just JB Weld them in.  Let that JB Weld set for a long time before use!

EDIT: Let's be clear that I have never actually tried this, so I have not verified if this mod does what it claims to do.

Monday, October 24, 2011

Cleaning up your electrical

If you have come across other pictures of my bike, you'd have seen my electric wires hanging out and simply clamped to the bike with zip ties.  These 2-stroke kits pretty much just have the electrical connections hanging out and I really hate that.  Also, I chose to zip-tie my CDI instead of using bolts(since it's plastic and apparently breaks easily), but that caused the CDI to move around and the plug wire would often be hanging out the side. 

Well recently, some guy was tailgating me and I made a sharp right turn and, well, I wiped out.  Got some road rash, but at least I got the opportunity to revise my set up!  I wanted something both visually and practically superior, so this is what I came up with:

  • I moved my CDI to the top bar on my frame.  That way it won't slide much even if you zip-tie it.  For some reason I just think it reduces clutter that way instead of having all the wires smashed up on the one bar on the bottom.
  • Shrink tubing: People say to solder the wires and use electrical tape.  I decided to go with something nicer looking and less sticky.  You can get shrink tubing at Radio Shack or anywhere that sells electronics supplies.  Just cut a piece, slide it over the bare area on the wire and roll a soldering iron over it to make the tubing shrink.  A heat gun may work well too.  It looks great and creates a nice seal to prevent shortage.
  • I took all the wires, including the ones coming from the kill switch, and ran them through a piece of flexible cable tube that I cut out.  This looks MUCH better than having all the wires visibly hanging out.  You can buy cable tubing from Radio Shack or Wal-Mart.  Then I just zip-tied the tube to the bottom frame. 
  • Used silicone sealant on the CDI(where the plug wire comes out) and where the magneto wires come out of the motor.  This in combination with the shrink tubing and cable tube should make this setup really water resistant.
P.S. Yes, I know that some paint is missing on my bike.  That's due to B-12 Chemtool and the fact that I spray-painted my frame.  One of the next things I plan on doing is patching those areas.

This post is sponsored by B-12 Chemtool: The world's most powerful paint-thinner!

Tuesday, October 18, 2011

Soda can head gasket

Sorry, I don't have any actual photos because the camera I used got jacked up and the photos were lost. :(

You don't need to spend money to replace your head gasket!  If the one you have is in mostly okay shape, you can cut your own from an aluminum soda can!

Simply cut a large piece of metal off a soda can.  Notice how it still retains the shape of the can?  There's an easy way to flatten out the metal; take a clothes iron and iron it as flat as you can.  It won't be completely flat, but you can get it flat enough to be useable.

If this doesn't make sense, the first part of this video shows how this is done.

Once you have made a nice piece of flat aluminum, trace your old head gasket on it with a permanent marker.  Then simply cut out your new gasket with a razor blade or an exacto knife.  Most of it is simple to cut, but the stud holes can be difficult; the key is to try cutting them a little larger than you'd think you'd need.

When you have placed your new head gasket on your engine and placed the head back on, push your bike forward with the clutch engaged to make the piston move.  If there are any air leaks, you should hear(and feel) the air come out around part of the head.  This is very important to check for because air leaks are very bad for your engine.  The first soda can gasket I made had too much cut off from the center and that's where an air leak came from.  I did a better job on my second soda can gasket, and so far there are no leaks.  If you want, you can use Copper Kote to create a better seal.

Are there any advantages to a soda can head gasket?  Other than costing virtually nothing, soda can metal is much thinner than the stock head gaskets, so if you're looking for both a quick fix and less compression, a soda can head gasket might be the way to go.

$5 solid tensioner mount

There are plenty of tensioner mods involving a spring, but sometimes people have issues with a spring-loaded setup.

This mod will give you a tensioner that is both solidly mounted and one that definitely won't fall into the spokes!

Saturday, October 15, 2011

Backwards cylinder jug

Isn't it strange how the stock engines have the intake on the rear and the exhaust in the front?  Of course the reason for this is to make these kits easy to install on most bikes.  But if you want a more logical approach to running your engine, it is possible to turn around your cyclinder jug so that the exhaust is in the rear and your carburetor in the front.  If you're looking to increase intake flow and to get the smelly exhaust behind you, then this might be a good mod for you.

Before you go spinning your jug around, please keep in mind that you have to do a few more changes in order to make your engine run properly with this setup.  Read more to learn what to do!

Candlestick velocity stack

A velocity stack eases the flow of air into the carburetor.  Wikipedia says that a velocity stack for an engine does two things:
  1. Allow smooth and even entry of air at high velocities into the intake tract with the flow stream adhering to the pipe walls.
  2. Modify the dynamic tuning range of the intake tract by functioning as a resonating pipe which can adjust the frequency of pressure pulses, based on its length, within the tract.
In other words, it works like this:

Instead of permanently polishing out the NT carb intake like others done, you can get a similar effect by having a velocity stack.  Bairdco made one out of a candle holder from a swap meet.

Thursday, September 29, 2011

$3 easy muffler end cap replacement

So the other day I was taking a nice morning ride on my booze-powered bicycle, and after all those times of me trying to get the end cap off the muffler manually, it came off by itself while I was on the road.  I stopped soon enough to go back and get it, but right as I got about 150 feet away a street sweeper just happened to come by and run over it!  Fortunately the end cap didn't get sucked up, but the cap was flatened and unusable.  I didn't want to ride without any back pressure for my engine so I had to peddle most of the way home.  The engine was also very loud without the cap.

I was frustrated because no matter how hot I made the cap with my torch, I couldn't bend it back to the right shape.  I thought I was going to need to make a new one and weld it on, but I found a solution that requires no welding and works just as well as the original!

The style of muffler I have is the one with the big baffle on the inside and a long tube protruding from the inside of the end cap.

Pretty much, the solution is to get a big steel washer and drill a hole through it.  Then bolt it on with a few smaller washers and a lock/spring washer.  And that's it!  Cost me $3 for the parts at Orchard Supply Hardware(my favorite hardware store).

Here are the parts I used:

  • Fender washer - 1/2" x 2"
  • Lock washer - 7/16"
  • 2 flat washers - 7/16"
  • 1 steel bolt - This can depend on your muffler so just pick the right one.
Any difference in performance?  Well since this homemade end cap doesn't have the baffle tube, the noise is just a tiny bit louder and I can see about 1mph better performance on hills!  Also sounds a little "throatier" than before!  If you lost your end cap and need a quick replacement, I'd say this is the way to go.  I've already road several miles with it and it stays on.

Monday, September 19, 2011

$10 homemade LED headlight

I've gone through 2 Bull(Bell) headlights and the large flashlight that I zip-tied to my handlebars slips around and isn't bright enough.  This seems like a great idea, and I think I'm going to do this! 

Sunday, September 18, 2011

Soda bottle fuel tank adapter

So ya wanna use a soda bottle as a fuel tank?  Well now you can!

As if our bikes don't already attract enough attention.  Still, wacky fuel tanks FTW!  Not sure if a plastic bottle is the safest tank around but I still like the idea.

EDIT: I have read that gasoline sometimes melt the green plastic bottles, so be careful.

Ethanol bicycle update

After reading around on the internets, I became very tempted to see if it's possible to clean up our china girls with E85(ethanol) fuel!  Few people have accomplished this; in fact I could only find one person who claims to run their motorized bicycle on E85.  I featured his video in an earlier post, although the video bears little information and I could not get in contact with the guy.  Never the less, I set out to see if I could replicate his results.

Today I picked up a gallon of E85 from a Conserv Fuel station, and some ester-based synthetic oil(as apparently regular and petroleum-based synthetic separates from the ethanol).  After tweaking the carb needle and replacing the float bowl gasket(which was melted by the ethanol), I got my bike running on booze!  Since it was night time I didn't want to take the risk of having the engine seize in the middle of the road, so I rode around my neighborhood for about 3.5 miles.  Ran pretty good, too!  I may still have to enlarge the jet in the carb, but with the needle at the 3rd position and with the choke on just a little, it seems to run just fine!  Even pulled me up some steep hills!

We'll see how this goes.  Tomorrow I'm going to ride further and continue to test out the E85 as bike fuel.  If I continue to get good results, I might make a video about it with more details.  But don't be shocked if my engine blows up sometime this week!

Join the discussion on motorbicycling.com!

UPDATE 2: I drilled the main jet with a #60 drill bit, but this may have been a mistake.  The engine now runs way too rich even with the needle at it's leanest setting.  This means that the engine does almost nothing but 4-strokes and it bogs down and it won't make it up hills.  It actually ran better with the stock main jet and the choke about halfway up.  Still, I want to get the most power out of the ethanol fuel, so my next plan will be to get an iridium spark plug since I think the problem might be that the normal NGK plug doesn't have a good enough spark to ignite the higher amount of fuel being squirted into the cylinder.  If that doesn't work, I'll simply have to buy a new jet and start again.  =/ That is if I could find a hobby store that sells a #65 drill bit so I can solder and redrill, which would be way easier.

UPDATE 3: I soldered and redrilled my jet with a #67(approx) from a Dremel drill bit set.  I've now got the bike running on ethanol with the slide needle clip on the second position, which is considered default.  No need for the choke anymore.  I'll wait for the plug to run a while to see if it's running too lean or not, but if this works out, the only things that would need to be changed to convert a bike to ethanol would be the main jet and some new gaskets.  The NGK B6HS spark plug works fine.  Turns out I got some gunk inside the fuel intake(on the carb) and not enough fuel was getting to the engine.  I also tried a Briggs & Stanton spark plug and that works well with it too.  Perhaps better, but I'll have to do more testing.  My muffler came loose during my last test run, and that caused my idle to go out of control and I almost went on Mr. Toad's Wild Ride!  Good thing my clutch and kill switch were hooked up properly!  Plus my gas tank has been leaking again and I'm pretty close to chucking it in the garbage.  I can't be riding around with fuel dripping on to a hot engine.  I promise to post a video once I am done fixing those few things.

Tuesday, September 6, 2011

Build your dream fuel tank with fiberglass!

You don't need expensive tools or metal-working skills to build your own custom fuel tank for your motorized bike!  If you're looking for an in-frame tank, or just something more sleek than the stock teardrop tank, fiberglass may just be the answer!

This instructables.com tutorial shows you how to make your very own fuel tank using fiberglass and fuel-safe epoxy resin!  The results look very professional, IMO.

What would make this project even cooler is if you could design your fuel tank as a computerized 3D model and paste together a prototype with Pepakura, and base your tank off that!

49cc engine running on E85 fuel

This guy claims to be able to run his 49cc bike engine on E85 fuel, which is 85% ethanol and 15% gasoline.  Many people think that ethanol can ruin your engine, so I don't recommend trying this just yet unless you have an extra china girl to spare.  Supposedly you have to use a larger jet in your carb, and the guy in the video says he added Marvel Mystery Oil to the fuel.  It's not clear what kind of 2-stroke oil he's using, since I believe the only oil that will dissolve in ethanol is pure ester-based synthetic 2-stroke oil.  Whether or not it's really currently possible, I'd love to be able to run my 66cc engine on mostly ethanol! 

Join the discussion on using ethanol with bike engines at motoredbikes.com!

Fuel fragrances for scented exhaust?

I came across this website the other day that sells "fuel fragrances" that are added to racing fuel to produce scented exhaust that help mask the nasty smell of burning fuel.  The scents you can buy include "Atomic Apple", "Burn Out Blueberry", "Rippin' Root Beer", and "Victory Vanilla"!  Though personally, I'd probably want to give my exhaust a minty smell, though it doesn't seem like they have that as an option.  Butterscotch would be pretty awesome too!

Some people find the idea of adding scent to your exhaust to be a "fruity" idea, but I think it's rather funny and I certainly wouldn't do it all the time.

But do these work with our little china girls?  I haven't tried it out, and I'm not sure anyone else has.  If you have any input, join the conversation at motorbicycling.com!

UPDATE: Pirate Cycles sells strawberry-scented oil that works in our 2-stroke engines!

Thursday, September 1, 2011

DIY bike sidecar

This isn't specifically a motorized bicycle mod, but I think it's a worthwhile [and not often talked about] idea.  

This Instructables.com entry gives instructions to making your own bicycle sidecar!

I'm not sure how safe it would be to have another person in this car, but for areas with low traffic, it may not be a bad idea!  Even better, you could mount a cooler on the trailer and start your own mobile ice cream business!  What better way to pay off that 66cc engine than by using a little engineering to turn it into profit!

You may be wondering if this would legally disqualify your bike as a motorized bicycle: Well, this can depend on the laws in your area, but usually bikes with 3 wheels still qualify, which is what's excellent about this mod!  I'd love to see someone do this with a motorized bicycle!

Cheap homemade reed valve

For those of you who don't know what a reed valve is, I'll quote wikipedia:
Reed valves are commonly used in high-performance versions of the two-stroke engine, where they control the fuel-air mixture admitted to the cylinder. As the piston rises in the cylinder a vacuum is created in the crankcase beneath the piston. This vacuum opens the valve and admits the fuel-air mixture into the crankcase. As the piston descends, it raises the crankcase pressure causing the valve to close to retain the mixture and pressurize it for its eventual transfer through to the combustion chamber.
Pitchfork311 on motorbicycling.com took an $8 chainsaw reed valve and made it compatible with an HT engine! 

EDIT: Please, keep in mind that you must modify other parts of your engine(like trimming part of the piston skirt) before attempting anything like this.  Supposedly, you can't just slap a reed valve on a motor and call it done.

Read more about reed valves on bike engines!

Simple air cleaner mod promotes easier "breathing"

It's a similar idea to having a ram air system, only it involves simply shearing off a bit of the tubes off to allow air to more easily pass into the carb.  Neat and simple idea!

Homemade clutch lock

One of the most irritating aspect to building an MB is having things fall out due to vibration!  Fortunately, some parts, like the clutch lock, can be fabricated out of hardware store parts!

Tuesday, August 30, 2011

V-twin HT engine!?!?

Apparently someone has done it!  Though it's not on the market yet, though.  Maybe someday!  I'll buy one if it's ever available!

EDIT: The Acme V-twin HT engine will likely never come out.  It's actually been a few years since the original thread about it, and there's been no word about it since.  Too bad, really!

Bicycle engine kits made in America

We all love inexpensive bicycle engines, but the sad part is that most of them come from China. 

That's why I decided to make a page dedicated to bicycle engines and kits that are Made In America!

Since they aren't very common, this page will start out with few listings, but I plan on continually growing this list so please check back!

Bumble Bee Bolt-on Bicycle Engines
Golden Eagle Bike Engine