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Discussion Starter · #1 ·
This is a nice guide for new cag owners to follow. I did not make this up. Had it saved to my computer. This was from another writer before the old site got hacked.

Section 1
The Basics!

What is a pocket bike?

A pocket bike is what it says it is, a miniature version of a real GP racing motorcycle, it just doesn't go as fast as one. There are many different makes and styles available, many of which look just like real racing bikes. They stand about 15 to 18 inches high depending on the model and brand and they weigh anywhere from 35 to 55 pounds. THEY ARE NOT TOYS!

What is a pocket bike for?

A pocket bike is not just your average ride around everyday scooter. A pocket bike is a high performance tuned racing machine… believe it or not! It must be well cared for and must not be misused or abused in any way.

How fast are these things?

Depending on which type you get will depend on the speed of the bike. The speed also varies according to the rider’s weight and road conditions. Most pocket bikes are capable of doing anywhere from 28-50 MPH.

What kind of protective gear do I need?

You should invest in a DOT approved helmet, pads and a body suit. Going at 25mph + does tear jeans and leave some pretty bad cuts and scrapes. NEVER ride without a helmet.. not only do you look stupid but you WILL hurt your self.

Do I Need A License?

These bikes are not for road use, so driver's licenses are not necessary. See your local DMV website or office for more information.

Can I Ride My Pocket Bike On Public Roads?

NO. They are not street legal. They do not possess headlights, turn signals, and brake lights. And do not have Department of Transportation approved tires (since they come with racing slicks). How Much Power Do The Bikes Have?

Stock is around 2.6hp. Simple modifications as mentioned on the parts page, including the Stage 1 2 and 3 kits, can increase power to 3.1hp at the tire. It is likely that the motor is actually generating 20% more than that at the crank. These engines are capable of more power than that if you are interested in spending the money for engine work.

What kind of motor does a Pocket Bike use?

Pocket bikes have 2-stroke engines.

Section 2

Well I have my pocket bike… what now?

Following the following steps will ensure that your first ride wont be your last!

1. Clean out your tank and flush with fuel to get any debris out.
2. Clean out the carb to assure it is free of debris.
3. Move the needle clip on the carb to the 5th position, which is the bottom notch if the needlepoint is pointing down.
4. Get an Airfilter
5. Pull the packing out of the exhaust.
6. Make sure all fasteners are tight and secure, possibly add loctite.
7. Make sure the gas cap is in some way vented so the tank does not vacuum. (Use a pin to punch 2 holes in the cap)
8. Make sure chain is well-lubed
9. Adjust your brakes so that they are not dragging too much, especially the rear. A dragging rear brake can cause your clutch to fry prematurely or break a clutch spring, among other things.
10. Mix your oil/fuel mixture accurately with good oil meant for 2 stroke bikes
11. Check over the engine bolts and steering head bolts for tightness, make sure wheel and steering head bearings are functional and not sloppy. Do not over tighten your foot peg bolts because they frequently break off.
12. NEW riders, read the starting procedures
13. Starting the bike- To properly start the bike, make sure the fuel **** is open, the choke is on, if the engine is cold. Make full complete pulls to the engine, while adding a little gas. Caution, do not add too much gas, your bike will fly out of control if it is not started on the stand! Even if you're starting it on the stand, it is not necessary to add too much gas. Once the engine has started, you can not turn the choke back to A if it was on the choke. Be sure to warm up the bike for at least a minute before riding off into the sunset.

Will it operate on pump gas?
Yes, premium pump gas should be used. Use fresh gasoline only, do not use any gas that has been stored for more than 2 weeks.
What oil is best to use?

Any good quality (brand name) pre-mix 2 cycle oil, preferably synthetic

Good oils:

Pro Honda HP2 Race, Maxima Castor 927, and Stihl are among some of the best.

1 pint = 16 oz

1 liter = 33 oz

1 quart = 32 oz


3 pints = 48 oz

3.2 oz = 15 fills [40:1]

2.6 oz = 18 fills [50:1]

General guide for the number of Oz to be mixed in one US gallon and what ratio it comes out to be.

50:1 = 2.6 oz oil to 1 US gallon of mid grade gasoline
40:1 = 3.2 oz oil to 1 US gallon of mid grade gasoline
32:1 = 4.0 oz oil to 1 US gallon of mid grade gasoline

By fills I mean the number of gallons you can mix.

What do I use to flush out my tank?

Whatever mixture you plan on using (ex. 32:1, 40:1 or 50:1) Use that same mixture to flush out the tank.

How do I break in my new Pocket Bike?

Start with a 40:1. Don't full throttle it and don't keep the RPMs at one speed. You want the RPMs varying up and down. Let it cool down after every 10-15min. of riding. Run the second tank on 40:1. After that switch to 50:1 using full synthetic of your flavor.

What position should the choke be in?

The choke should be in the upward position when your doing a COLD START, and it should be in the down position when your riding or doing a WARM START.

Section 3
Performance Tips

Performance! How do you get more?

Carb- The bigger the carb (meaning bore and jets sizes) the more fuel you can introduce to the cylinder. A venturi bore speeds up the airflow across the main jet and pulls more fuel into a somewhat compressed mixture. (there is a limit on how large to go though)

Reeds- Stiffer reeds close tighter and faster sealing your precious air/fuel mixture into your case. this aids in the pre compression stage of your mixture. Stiffer reeds also don't flutter at higher rpm, which creates turbulence before the charge reaches the combustion chamber.

Ported head- (this also includes the porting of the case at the transfer port bottom) This allows more fuel/air to enter the combustion chamber via lesser resistance and larger cross sectional area. (up to a limit, this gets WAY more complicated) This includes matching the ports between the case and the head and smoothing any obstacles to the mixtures flow.

Indexed/matched piston- Indexing the piston (the way I do it) effectively increases the transfer port size at the top. It also advances the intake timing, allowing more fresh charge into the combustion chamber. An angled "index" will guide the charge up and to the rear of the chamber which will swirl and create a vacuum at the front of the chamber, this helps scavenging and creates more space for the return pulse charge. This makes your power band peak stronger and allows your expansion chamber to be more effective.
Matching the piston is cleaning up the underside to maximize flow and to enlarge the transfer port at the bottom, this is mostly effective on the Cag piston port style motors.

Tuned pipe- A properly tuned pipe will create a return pulse at precisely the right time to pack the left over fresh charge back into the combustion chamber. At your power band peak this essentially acts like a turbo.

Performance clutch- I'm mainly talking about the clutch engagement time here. If a clutch is set to engage at later rpm, you can build more horsepower before it engages. This will give you substantially more acceleration. The motor will also rev faster at the lower rpm due to the lack of a load on the motor. This also acts as if you have a lighter piston/crank, until engagement that is.

What should I mod first?

1. Air Filter induction kit / exhaust can upgrade

2. Re-gap spark plug spacing to .025 Inches. You may also want to pick up the NGK BM7A

3. Fuel filter and Higher Quality fuel line

4. Carb porting and polishing

5. Primarily an engine teardown, modification and reassembly. It includes bumping the compression, indexing the piston and other porting. Depending upon the builder and methodology, it can be done to yield more bottom end, midrange or top end power.

How do I maintain and keep my bike running smooth?

The spark plug must be clean, and must be replaced promptly when signs of wear begin to show. The condition of the spark plug can tell you a lot about how your motor is running. The spark plug should be a light brown or golden color.

The air filter is used to clean the air going into the gas motor. Periodic cleaning of this filter is recommended to protect your motor against the damaging effects of dirt and abrasive particulates. Your air filter can be located on the back and it has 2 screws.

The chain on your gas-powered scooters should be lubricated before every ride. The chain should also be checked for tightness on a regular basis. If the chain is too loose a popping sound can be heard and the gas-powered scooter will jerk under acceleration, or the chain will just jump off altogether. If the chain is too tight it will be noisy and bind, this can be felt by pushing the scooter with the motor off.

The carburetor has many adjustments on it and it is recommended that experienced persons make these adjustments only, however we will point out the major points. The carburetor is responsible for pumping the fuel and mixing it with the air at a precise measurement. The carburetor does this with very small diaphragms, orifices and ports, which are easily clogged by contaminants. This is why is extremely important that you use only clean new fuel mixed with 2-cycle oil. KEEP YOUR CARB FREE OF DEBRIS!!!


24,145 Posts
If it's a older bike it is the 47cc engine, 40mm bore, the 49cc is 44mm bore. The 49cc heads are 1/4 bigger and fins look a little different.

Bicycle with Engine
881 Posts
Depending on the stroke length, if you have a 40mm piston, the displacement would be either 38cc or 40cc...... Some members on here have reported having different length strokes in their engines; My Cag engines measured 32mm stroke, w/ the 40mm piston which is 40cc. If it were 30mm stroke, It would be 38cc... My piston ported engines with 40mm pistons measured 34mm stroke which is 43cc.

One easy way to tell if you have a 40mm or 44mm piston/cylinder is by looking for the big solid square on the cooling fins on the clutchbell side of the engine. The smaller 40mm bore cylinder is on the left.


24,145 Posts
So, 42, you got 32 and 34mm on the strokes of reed & piston port engines. CAM2 got 30 & 32, and that's what I thought I measured, but roughly, not a real accurate check. So, that means there could be both kinds? Thumplump got 32 & 34mm also. I can't change the stroke, so I put the piston on the rod & cylinder over it, on a 2 pc cyld/head kit, and see how much Sqiush space there is and cut down the top till I get what I want. Don't like the one piece cyld cause you would have to raise the compression by machining the bottom mating surface thinner, and that's not easy.

Bicycle with Engine
881 Posts
I'm thinking that some ended up with engines w/ longer strokes than others. I'm pretty sure that out of the 3 ways I measure, my calculations are correct. I also wanted to see if that 30 year old reeded backpack blower I had actually stated the correct displacement of 37.7cc and it was right. It has a 40mm piston and a 30mm stroke. I think that since the Cag engines were ripped off these blowers, they were also improved by adding a longer stroke crank and as well as a few other subtle differences.

A member on here asked me if they could buy those cases to build a stronger Cag engine which I was already in the process of trying to do... I found that the 32mm Cag cranks will not fit in the 30mm blower engine cases. The counterweights stick out too far... The connecting rod on the Cag crank is 8mm longer than the blower crank and the piston top height is different as well. So, the cylinder base sits at a different height and the port timing is way off... If I found a 30mm stroke crank and swapped the connecting rod on, then I could have a shot at building it up.....


24,145 Posts
You can grind the top of the piston .050 to .060" if it sticks up to far with the longer rod, if you have enough space. The crank part I would have to see the difference, can you mod it to fit.
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