2 Stroke Kit Installation

View 2 Stroke Bicycle Engine Installation Video Here

View Illustrated Wiring Diagram Here

STEP #1 Mounting Engine to your Bicycle

Standard mounting to 28mm tube

1. The engine mounts in the bike frame “Vee” above the peddle wheel sprocket. ( see above pic. )

2. Consider using Masking or Duct Tape on the front down-tube & seat tube of your bicycle to protect the paint finish while test fitting the engine to your donor bike. If the distance between the two bars exceeds the engine mounting span then additional spacers or welded brackets are required. Mount the engine to the seat tube first and then fit to the front tube.

Engine Forward Mount Installation:

All kits come with a special mount plate for large down tube frames as shown below in figure 1.

Many different bike frame sizes and angels require mechanical challenges to the installer when mounting the front engine to the down tube frame. When looking for a donor bike it is best to compare the engine to the frame before purchase of a new bike. Note: Seat tubes of 28 to 29 mm work best. Attach engine to seat tube first, position, and then determine front mounting.

Figure 1

This adapter plate is included in the kit.

For bikes with large front frame tube: Use 1/4" thick 1-1/8" x 2-1/2" steel plate with one hole in the center for a bolt to go through a drilled hole in the tube frame and two holes for cap screws to go into engine block. Additional spacers may be required depending on the bike.

3. If the rear frame tube from the seat down to the pedal sprocket is too small to fit the rear engine mount, a rubber shim can be made from an old bicycle rubber inner tube. This also helps reduce engine vibration.

4. After the desired engine location is determined mount the engine to frame. Lock nuts and or use of Loctite is recommended to avoid loosening due to vibration.

Note: All threads on hardware nuts and bolts are metric.

STEP #2 Chain Wheel Sprocket Installation

Sprocket Installation on Rear Wheel

44 tooth - 50 tooth or 56 tooth chain wheel sprockets may be installed on Coaster Brake wheels or any wheel without drum brakes or disc brakes; In some cases it may be necessary to enlarge the center sprocket hole to fit axle hub. 9 hole sprockets are made for 36 spoke wheels. For long life it is best to use with wheels having 12 to 14 ga. Spokes.

Figure 2

Attention to true alignment with
engine drive sprocket is
essential to keep chain from
coming off. A chain idler is used
to tighten chain if needed.

The Drive Chain Sprocket has a 36.9 mm dia. center hole and mounts on axel hub on the left side of the rear wheel against the spokes dish side in. The sprocket must fit over the hub in a perpendicular plane with the axle. This insures that your rear chain sprocket spins true with the rear bike wheel.

*NOTE: On some older bike axle hubs like on coaster brake models it may be required to slightly enlarge the sprocket center hole to obtain a flush, and concentric fit next to the spokes. This is best done on a engine lathe by a professional machinist. It is also recommended that the rear wheel be re-spoked to 12 ga. spoke wires to insure long life. Most any Bike shop can do this operation for you.

Applying thread adhesive and equal tightening of the sprocket bolts

This keeps the chain sprocket true with axle and free from wobble while spinning. With bike upside down spin wheel and check sprocket for wobble. The chain can jump off the sprocket if the sprocket installation is done incorrectly. (Note: For the professional installation the Gru-Bee special coaster brake 26” wheel with a wide spoke flange for quick direct chain wheel mounting is available. See below for details:)

1. For kit sprocket installation, locate sprocket on axel hub with curved side next to spokes, shinny side in.

2. If not pre sliced, cut the rubber isolator to the center, in order to fit INSIDE the spokes and around axle. Install the split steel retainer plates next to the rubber isolator and insert 9 bolts.

3. Secure with 9 bolts compressing the chain sprocket to the spokes. Note: Rubber isolators may be needed on both sides of sprocket for chain alignment on some non-coaster brake bikes.

4. The Chain Sprocket on the Wheel must align within 1/2 cm to the Chain Sprocket on the Engine.

5. The wheel chain sprocket is mounted with teeth-out and dish-in next to spokes. See Figure 2 above.

Note: Mount Sprocket bright chrome dished side next to spokes.

9 slot Chain Wheel Sprocket Installation mounted dish side inward:

The drive chain can be easily shortened to the correct length. Special tools are required to remove and replace the master link when shortening the chain by removing links. Ideally, both your pedal drive chain and your engine drive chain should have the same tension.

1. Remove left rear cover plate from engine. This is the plate next to and under the clutch swing arm.

2. Use supplied spark-plug wrench to turn engine crankshaft sprocket to feed chain around it. Do not pry sprocket with a screwdriver or similar object as it is made of harden material and may fracture.

3. Fit chain, measure and remove excess links to assure proper length. Proper length is when top side of drive chain has ¼ inch to ½ inch deflection with the bottom side of the chain loop tight.

4. Reconnect the master link, and replace cover plate on engine.

5. Chain tension adjustments can be made by moving rear wheel. If both chains can be made to have equal tension then installing the idler assembly will not be necessary. Mount the chain idler on the wheel strut if the engine drive chain cannot be made as tight as the pedal chain.

6. Install supplied chain safety guard by attaching to engine and wheel axle struts.

STEP #3 Ignition Coil and Engine Kill Switch Installation

CDI Ignition Coil

Kill Switch

1. Mount CD ignition coil on bike frame, close enough to attach coil wire to spark plug. Mount as far away from exhaust pipe as possible to avoid heat damage to semiconductors in CDI module.

2. Attach CD ignition coil wires to same identical color coded wires coming from engine.

3. Install Engine Kill Switch on the handlebar or use kill switch on left hand grip.Attach kill switch wire to white wire coming from engine. This will ground ignition and stop the engine when the red button on the kill switch is activated.

4. Route all wires away from engine exhaust heat. You may secure wires with a plastic zip ties (not provided).


Operation of engine without stop or kill switch installed could result in personal injury if an emergency stop is required! The only alternate non recommended way of killing the engine is by releasing the clutch lever with bike brakes on and engine at slowest idle.

STEP #4 Clutch Cable Installation and Adjustment

1. Install clutch lever to left side of handlebar and attach cable end to lever.

2. Squirt oil down the cable sleeve: Route clutch cable through the ball-mount on motor with the big spring around the cable jacket and ahead of the ball mount. The big spring serves as a cable heat shield.

3. Insert cable wire through small spring and route through clutch arm and attach brass cable-end and screw. Adjust cable tension to allow very slight play in lever. Handlebar clutch lever or twist clutch must be in the released or outward position to complete this operation.

4. Activate lever a few times, and check clutch arm for slight free play again. About 1/16” free play is OK. Re-adjust if needed. Basics of clutch operation: The clutch lever pulls the cable that moves the clutch arm. In turn the clutch arm pushes a rod through the motor that pushes the clutch plate. ( similar to a car clutch.) Releasing the clutch lever engages the engine torque to the drive chain. The clutch allows engine to start, and engage or disengage engine torque to the drive chain. When the bike is in the pedal mode the handle bar clutch lever is locked inward in the catch notch. The bike then operates in default as it would without any engine. Periodic clutch adjustment is necessary to maintain efficient operation *NOTE: Cut off excess cable from clutch arm, before operation, to avoid possible interference with pedals, chain, your legs, etc. See Figure 3.

Figure 3

STEP #5 Carburetor and Throttle Installation

Be sure to check carb. air cleaner attach screws for tightness before installing engine.

Air cleaner screws coming loose and entering engine is not covered by warranty.

Procedure for attaching throttle cable to carburetor throttle slide: The small stop on the cable wire slides through the long groove of the carburetor brass cylinder slide. It held in a slot at the end of the cylinder.

The spring is placed inside the cylinder slide and is compressed when the throttle is twisted. Be sure it is seated all the way inside the cylinder. The spring then forces the throttle to return. For this to work properly the throttle must twist freely on the handle bar in both directions prior to the cable being installed.

1. Install twist grip throttle on right side of handlebar end. On some bike handle bars it may be necessary to ream out the handle ID to fit the bar so that the throttle will twist freely.

2. After installing cable inside the carburetor mount it on engine intake tube and tighten clamp screw. Mount carburetor as level as possible. Note: The air/fuel mixture screw should be preset at 4.5 turns counter clockwise from the totally closed position.

*NOTE: Do not back-off screw more than 4.5 turns or vibration may loosen the screw and cause it to fall out. If this situation occurs, stop engine immediately and replace mixture screw.

STEP #6 Fuel Tank Installation

1. Attach fuel petcock to tank. Use Teflon tape to seal threads. Careful not to strip threads.

2. Mount tank on bike top crossover frame with two supplied brackets and nuts.

3. Attach fuel line from tank to carburetor.

*NOTE: Filters are contained in the petcock and in the carburetor inlet. If engine runs poorly clean the valve filter as residue from the tank may have clogged it. It is highly recommend that a tank liner coating be applied inside the tank before installation. This product is available from motorcycle dealers.


Gas and Oil Mixture for Fuel ratio

Engine break-in/wear-in is a crutial step.

The engine is a 2 cycle design, therefore, a gasoline/oil mixture is necessary.

An ISO-L-EGD/JASO-FD rated synthetic oil is required for engine use. We highly recommend Stenz Synthetic Blend 2-Stroke Engine Oil.

Failure to use non-approved oil will void all warranties and may violate EPA regulations.

Break In Steps:

1st tank...................20 parts gasoline to 1 part oil (Do not run engine past 1/2 throttle)

2nd tank........................20 parts gasoline to 1 part oil (Do not run engine past 3/4 throttle)

Additional tanks...............50 parts gasoline to 1 part oil (Full throttle OK)

*NOTE: do NOT use E-85 gasoline.


Remember safety first: Wipe up any spilled fuel. NEVER fuel a hot engine or smoke while fueling. This could result in sudden fire, personal injury. Always move your motorized bike at least 10 feet from any fueling area before attempting to start it. Never leave the tank fuel cap off after fueling as rain water will contaminate the fuel and cause engine failure.

Maintenance Section

#1. How to Adjust Clutch if signs of slipping or squealing occur:

1. Disengage clutch by pulling handle bar clutch lever inward and lock into catch lock.

2. Remove right side engine clutch cover and remove small locking screw on center *Clutch Adjust Nut.

3. Pull clutch arm on left rear engine inward. Back off *Clutch Adjust Nut ¼ turn counterclockwise.

4. Release clutch lever and check for slight clutch arm 1/16” free-play on opposite side of engine. Readjust *Clutch Adjust Nut as required to get required 1/16” clutch arm free play.

5. Tighten *Clutch Adjust Nut on clutch plate clockwise until just snug.

6. Then re-install small locking screw in outer edge of *Clutch Adjust Nut.

7. It's good idea to place a small gob of grease at gear mesh area. Use grease sparingly! Then replace cover.

8. Squirt light grade oil down clutch cable sheathing to reduce friction and make for easy lever pull.

*Clutch Adjust Nut

#2. Carburetor:

After every 5 hours of operation check the adjustment of the mixture screw by rotating screw clockwise until seated and then rotate screw 4½ turns back counterclockwise. Depending on dusty riding conditions, clean air filter every 5 to 20 hours of operation by removing the filter cover to access the screen and element. Wash element with a degreasing agent such as Simple Green™ or Purple Stuff™. Be sure element is completely dry before re-assembly.
IMPORTANT: If engine runs poorly clean tank shut off value filter.

#3. Spark Plug:

Remove spark plug and inspect for excess carbon build up. Clean, re-gap to .028- .034 of an inch if necessary. Check plug after every 20 hours of operation. New spark plugs are available from your selling dealer. Be careful using aftermarket spark plugs as heat range and threads differ greatly. Extra plug is included with kit.

#4. Exhaust System:

After 20 hours of operation check exhaust pipe for excessive oil and carbon build-up. Be sure to use supplied support strap to secure exhaust muffler to a solid anchor point on bike frame or engine.

1. Remove exhaust pipe cap by loosening the retaining screw.

2. Pull cap and baffle out of pipe.

3. Clean with degreaser, rinse and dry.

4. Re-assemble

*NOTE: Excessive periods of low speed operation, idling or leaving fuel petcock in the “on” position during shut down periods may cause the pipe to become clogged with unburned fuel.

#5. Chain:

Every time bike is ridden check the tension of the drive chain by:

1. Rolling to bicycle forward to remove slack from the bottom of the chain.

2. Find the center and push downward on the top of chain while measuring the deflection.

3. Tighten chain if deflection is more than ½ inch.

#6. Head Bolts

Tighten all fasteners after each five hours of operation. Most important to check Cylinder head bolts : Tighten in a X pattern to 8 to 9 ft/lb. for 48cc 55cc; 12 ft/lb for 70cc 80cc engines using a torque wrench. A two piece cylinder and head design engine requires head bolts be kept tight. Important: Check head bolts before each and every long ride, vibration can cause them to loosen and blow a head gasket. Caution: Do not over torque or head bolts may break off. ( Twisted or broken head bolts due to over tightening is not covered by warranty. )

#7. Right Side Gears:

Remove cover plate and keep small amount of heavy grease on gear train. Do not over grease as leaks will occur and also may adversely affect clutch operation. Regular greasing if required will help reduce gear wear and keep gear train quiet.

#8. Left Side Drive:

Routinely pack grease in the shaft hole behind 10T drive sprocket and also in cover bushing hole. This will also help deduce noise.

General Information

Obey all traffic regulations. Always wear a helmet while riding. Remember that you are riding a motorized bicycle and other traffic may not be able to see you. Never operate your motorized bicycle on a pedestrian through way or sidewalk while the engine is operating. Never operate your motorized bicycle in an unsafe manner. Check local and state laws before riding on streets. Using larger than 49cc for street use in not legal: WARNING! ALWAYS wear a helmet while riding.

If you have any questions or suggestions, please contact us.