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!

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

Friday, August 26, 2011

How to fix a slipping clutch

As well as hacks, I also like to feature some maintenance tips, since the manuals that come with the kits don't do quite enough to tell us how to maintain our bikes.

This excellent video demonstrates how to clean out your clutch and fix it from slipping.

As a word of caution to anyone who tries this, please remember to wear goggles and gloves!  Brake cleaner is nasty stuff and try not to get it on your skin!

Getting a bicycle engine kit in California

Due to CARB regulations, it can be tough for newbies in California to buy a motorized bicycle kit!  Many distributors refuse specifically to ship to Californians!  

Now I have made a page with a list of all distributors I know of that are California-friendly!

Sunday, August 21, 2011

Choke lever mods

That choke lever is such a hassle to deal with when starting a ride, right?  It's even worse for me because since I replaced the stock fuel line with some thick high-quality line, for some reason that causes my fuel filter to be right in the way of the choke lever!  Even so, why should we have to take our eyes off the road just to get our engine starting quickly and nicely?

These are some relatively simple improvements that will give you easier control to the choke.  It basically works the same way your clutch lever does, only it connects to the choke lever.  And now it makes the choke lever spring-loaded!  

Get more information!

This is another easy mod to the choke lever, which is probably a bit cheaper to make.

Pro-Tip: Is your engine randomly 4-stroking and bogging down?  Have you fiddled with your carb needle a million times to no avail?  Well your problem may just be your choke lever!  That's right, your choke lever.  Recently my engine has been bogging down randomly and I could barely make it up the hills I normally scale with ease, and I figured out that the choke lever has become loose from use and that caused it to move upward from engine vibration!  So if you think that's your problem, make sure to tighten your choke lever so it's not too loose.  Then watch your bike fly!

Keep that idle screw in place!

I, like many others, lost their idle screw early on.  I made the mistake and found another screw that fit in, but it was so long that when I buried the screw it actually bent the carb needle!  But anyway, that's getting off on a tangent.

The spring on the stock idle screw simply doesn't do enough to keep the screw in place, so a lot of people lose their screw because of vibration.  If you've been around the MB community enough, you might have heard of making a "safety wire" so that the screw doesn't get lost.  I think this idea takes that a step further.

A wingnut and a rubber washer keeps the screw in place!  Theoretically, this would mean you wouldn't have to worry so much about adjusting the screw because of vibration.  When I get a new idle screw, I'm definitely going to be doing this.  You might even get away with using a spring washer if you wanted.

Replacement idle screws can be purchased at thatsdax.com.

You might also be able to find a compatible screw at a lawn mower store.

DIY Manual Shifter Kit

Sometimes having a single drive sprocket is a bit limiting.  A shifter kit is a very attractive add-on because it can give you the powers of multiple sprocket sizes.  But those kits are expensive!  If you're willing to settle for a more manual setup, you can make your own multiple-sprocket setup.  Max350 from motorbicycling.com installed a 36 tooth sprocket over a 44 tooth sprocket, and made a segment of chain that's removable with two master links to fit the chain on to a the larger sprocket.  Simple, and does the trick if you're willing to carry plyers with you on a ride!  Although I would bet that you could make this setup even simpler by using a spring-loaded tensioner!  You wouldn't even need to fiddle with master links! 

Saturday, August 20, 2011

Air bike horn

When I was first putting together my motorized bike, I bought an $8 kit off ebay that contained turn-signals, a functioning brake light, and a horn.  While I'm still satisfied with the former, the electronic horn was a bust.  When I first put it on my bike, it sounded loud.  That was before I started the engine.  After a week of riding with it, somehow the vibration caused the speaker to rattle and now it doesn't work at all.

The Airzound bike horn, however, is the perfect solution.  It's an air-powered horn, like an airhorn that you would use at a sports game.  But why not just use the cheap air-horn that you'd bring to a sports game?  Well, you could.  But the Airzound doesn't require cartridges or batteries; It includes a pump to charge it up, and it lasts up to 30 blasts per charge!  And it's 115 db loud!  This is the best bike horn I've found, and it's certain to increase your presence on the road!

Here's a video of it in action!

Thinner head gasket for more horse-power

Some people run their engines without a head gasket for higher compression, thus slightly-greater horse power.  But this can be risky and can result in air leaks that can harm performance and the engine.  Instead of throwing out the head gasket all-together, just get a thinner one!

Sick Bike Parts sells replacement head gaskets that are thinner than the stock gasket, and better yet, they're made in the USA!

49cc/50cc Gasket with 6mm stud holes
66cc/80cc Gasket with 6mm stud holes
66cc/80cc Gasket with 8mm stud holes

Replacing your spark plug wire

Well today my spark plug wire failed.  I pulled the plug off the spark plug and out came a few pieces and a mangled little brass cylinder.  Now it doesn't even stay on the plug and easily falls off!  It's not hard to find a replacement spark plug wire for our engines on the internet, but I'm an impatient guy and I like quick solutions.  So I took a chance and bought a spark plug wire from NAPA Auto Parts.  I showed my stock bike spark plug wire to the guy at the counter, and he gave me the closest thing he could find.  I walked away with a Belden distributor end-type spark plug wire(part #BEL 701050) for about $8.  I cut off the other end of the wire(the part with the larger plastic plug), and screwed it into my CDI just like with the stock spark plug wire.  And it works!  In fact, it's longer(14"), more flexible, and it holds on to the spark plug more tightly.  I don't notice any improvement performance-wise, but it works just as well as the stock and makes an excellent replacement!

Thursday, August 18, 2011

Vacuum cleaner air filter

The stock air filter stinks.  Logically, a vacuum cleaner filter should work even better, right?  This mod is made entirely with hardware store parts, and it's very professional-looking at that!  Why buy a new air filter if you can make your own for cheaper?

Soda can muffler end-cap replacement

Most of the time we can't wait 5+ days for a new part to ship, so you've gotta do what you've gotta do.  Since the aluminum on the top of a soda can is considerably thicker, this could work.  JB Weld should work at least temporarily, but in my experience it takes even longer than said in the instructions to let the glue set so that it can withstand the heat.  Since there isn't a whole lot of pressure put on the JB Weld, it might definitely hold.

UPDATE: If you don't want to use JB Weld and you want something superior to the OEM end cap, check out my $3 end cap replacement!


If you have the equipment for welding, then this mod is for you.  Having dual tailpipes will help give you more power similarly to an expansion chamber, and it should spread out the airflow.  Not quite as good as an expansion chamber, but the next best thing.  Still, I wonder if the time and money that goes into this couldn't have just been spent on a BGF or SBP expansion chamber?

Tuesday, August 16, 2011

Low-profile "ram" air system

Yet another post from an ancient motorbicycling.com thread I came across.  User pedalpower took what looks like a tobacco can and mounted it on the back of the carb to "catch" more air.  A very interesting idea, and a very inexpensive mod... but does it work?  This is one I definitely want to follow up on.  I can find no other example of this.  The only thing that does something similar is the "boost bottle", which is generally considered to be a bust.  However the boost bottles push gas into the intake after the carb has mixed air and the fuel, but this mod in theory would help to push more air into the carb as the bike gains speed.  Very interesting!

UPDATE: I tried doing this today using the bottom of a pineapple tidbits can.  I'm not sure how much more power it really gives the engine, but the engine seems to run nice and smoothly with it attached.  It seems to make it easier for the engine to inhale, so there's a bit less 4 stroking.

UPDATE 2: So far, this seems to be working really nice.  I'll upload a picture at some point.  I actually had to remove it the other day in order to fix the air filter(the carb sits really close to the frame).  I rode my bike without the ram air, and I could really tell the difference.  My bike runs very well anyway, but I could tell that the bike was running slightly richer than it needed to.  Some people say that having a ram air system leans out the mixture too much and that it wrecks the vacuum that's created between the carb and the engine and that it will eventually ruin the engine, and while that may be true for a pipe-based ram air, I think using the bottom of a can works great.  The NT carbs tend to run the engine a little richer than necessary anyway, and I think having a simple setup with something to "deflect" moving air into the carb nicely balances it out.

How to SeaFoam your MB engine

I've seen plenty of videos on using SeaFoam on Miatas and Jaguars, but I haven't found many instructions on how to use SeaFoam on our Happy Time engines!  This video is straight forward in showing just how this is done.If you're trying to figure out how to get rid of that black stuff from your piston(carbon deposits), then this is one way to do that.  SeaFoam is a petroleum-based cleaner that's about $8 - $10 for a can, and by injecting it into your engine after a warm-up you can [attempt to] get rid of those evil carbon deposits!  The only by-product is some thick white smoke coming from your exhust(to show you that it's working).Since our engines don't have induction tubes like some cars have, this method involves running the engine without the air filter and gradually spraying in SeaFoam through the carburetor, spraying in just enough at a time that the engine doesn't stall out.A cheaper alternative to SeaFoam is B-12 Chemtool, but SeaFoam is a tried and true product.

Too lazy to buy a new air filter? Break out the drill!

Whether you don't want to buy a better air filter or you're waiting for a new one to get shipped, here's an extremely easy mod that will improve air-flow and boost performance!

Simply break out the power drill, and add extra holes on the back of the stock air-filter cover!  And that's it!

I've done this myself, and you can definitely tell the difference!  Want to go even further?  You can improve airflow even more by cutting off the 4 tubes at the bottom of the cover!  Who needs 'em?  Sometimes they even get in the way of the frame too, which is actually the main reason I clipped them off.  You can also try cutting out as much of the inner bracket [that keeps the air filter in place] as possible!  The less that's in the way the better!  It all adds up, after all.

Opti-2 100:1 mix

This is an old discussion, but I'll bring it up for those who haven't heard of this.

Are all used to running our bikes just fine on a 24:1 or 32:1 mix, but some claim to be able to run on a 100:1 mix using Opti-2 oil.  Now I'm still a bit skeptical, but I may have the cajones to try this soon once I've gone through the tank of 32:1 sitting in my garage. 

So what could a 100:1 mix do for us?  Well, it would mean more gasoline and less oil burning during the combustion process, and it would mean cleaner exhaust.

Improving carb airflow?

This guy(whiplash) from motorbicycling.com took a different approach to modifying the stock NT carb.  By removing the choke and creating a velocity stack, he claims to have gained more than 4mph speed!  I've yet to try this, but it seems very plausible since many of us have seen results by port-matching(thus creating better airflow). 

Monday, August 15, 2011

MB Survival Kit

With MBs, the only thing most of us ever think about is how to enhance engine performance.  But if you think about it, safety is even more important on these homemade contraptions that can fly apart at any minute.  This Instructables article shows an easy way to protect ourselves when out on the road.  It's basically an Altoids tin with contact phone numbers, some bandages and money.  All you have to do is strap it to your bike!  One of these tins would as well be good to contain some basic tools for bike repair, I would think.

Choosing a better spark plug

The LD spark plugs that come with most kits, while adequate to get a motorized bike functioning, may not have the most consistent sparking.  In this video is a demonstration between a normal NGK spark plug and an NGK iridium spark plug.  

As you can see, the iridium spark plug has more consistent and even arcing than the normal plug.  Replacing the stock LD spark plug with an NGK spark plug would already increase engine performance, an iridium NGK spark plug could mean even greater performance!  

Iridium plugs can be purchased at sickbikeparts.com.  Remember however, that when replacing the stock spark plug with any kind of spark plug, to make sure that the plug is not going too far into the cylinder(which may cause it to collide with the piston).  Simply remove the head of your engine and compare it to how the stock spark plug fits.  If you think it goes too far into the cylinder, add some washers to the plug to fit.

Getting traffic lights to detect your bike

Depending on where you live, traffic lights work by using metal detectors underground to see if there are cars waiting to go through the intersection.  This works fine for cars and motorcycles, because they have very large frames.  MBs are quite small and often do not trip the traffic lights.  In other words, you may find yourself sitting at a red light for a very long time and the light might only turn green when a car shows up.  

This motorbicycling.com thread talks about solving this problem.  The solution I went with was to place on my bike a large neodymium magnet.  These magnets are extremely strong and will sufficiently trip the sensors at traffic lights.  All you have to do is obtain one and stick it somewhere on your bike(it stuck under my kickstand just fine).  You can get a magnet from gaussboys.com, or you can harvest one from a bricked hard disc drive.

EDIT: Here's a Youtube video by Kip Kay explaining how this is done.

NOTE: Beware when handling strong magnets.  Never put 2 neodymium magnets together and beware of getting your fingers pinched when putting a magnet near something else magnetic.

Soda can air filter cover

If the plastic cover on your stock NT carb breaks some how, it turns out there's an easy way to replace it!  Looks like the bottom of a soda can with holes makes for a functional cover for your el cheapo air filter.  Seems mainly like a stopgap, but perhaps making a cleaner cut and polishing off the labels might actually make this thrown-together cover look rather stylish!

Clutch Pulley

The clutch system on these engines is rather simple, and for some people it takes a bit of strength to disengage the clutch.  I remember when I first let my girlfriend ride my MB and she had a difficult time operating the clutch handle.  This mod should help solve that problem.  I've seen/heard of clutch pulleys before, but they either involved welding or modding the clutch cover.  With this hack, all you can make your own pulley from hardware store parts!  The only thing I might do when I make one of these would be to find a way to fasten the clutch cord tube to the bar rather than using JB Weld, but JB Weld usually holds up nicely anyway.

You can also buy a similar prebuilt clutch pulley(aka roller bracket) from Al.Fisherman!

Make your MB snow resistant!

I've never had a need for this, and I don't know if it's even possible to buy legitimate snow chains for a bicycle, but this seemed like a quick n' easy mod to give you more friction in snowier climates.  All it is are zip ties that have been placed over the tires and around through the wheels.  I think zip ties are one of man's greatest inventions!  Though since MBs are mostly for recreation, I'm sure this would mostly come in handy in desperate situations.

Locking Gas Cap

Unfortunately, the world is overrun with jerks.  Since us MB riders are good people, we deserve some protection.  MBs are probably as vulnerable as a vehicle can possibly get, and there's always the chance of some junior high school kid from putting dirt or sugar in our tanks.  My car has a locking gas cap, and so I thought why not have one on our bikes as well!

These are very hard to find, but apparently there's a site that sells these locking gas caps for mopeds that may also fit our stock teardrop-style tanks.  

UPDATE: The locking gas cap from ScootUSA reportedly works with the stock teardrop fuel tank.

Ammo Box Saddlebags

 This mod wasn't actually done to a motorized bike, but it should apply the same.  Many of us would like to do anything to make our MBs look more like motorcycles, and I think adding cargo capability definitely helps.  This is an especially good mod for those who's bikes are painted army-green, like my own MB.

Ammo boxes are also relatively cheap and there are many of them for sale in pairs or more on eBay.

Copper Pasta Tin Gas Tank

Looks like a great way to add a "steampunk" look to your motorized bike!  This is one of the best home-made fuel tanks I've seen, and the best part is that it won't have rust in it like the stock tanks often do!

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