Skyhawk Instructions


GT5A > 66cc / 47 x 38mm bore and stroke: 43mm Wide mt. / angle fire, / pedal start:
GT5A-ES > same specs as GT5A except has combo electric drill start and pedal start.


Installation Kit Box Contents:

One 2 cycle gas engine, Special Black Catalytic exhaust muffler; Steel 2.5L Fuel Tank zinc plated inside; Drive chain; Chain guard; 44T Wheel Sprocket with mounting hardware for 36 spoke wheel; Ball Bearing Chain idler: Push button clutch lever, Special modified NT Carburetor. High quality Rubber fuel line, CDI Ignition module, Throttle with kill switch: Optional: Tool kit with extra spark plug & gaskets;

Step #1. For warranty purposes and future parts service record the following information and save.
1. Engine serial number found on the right side of the crankcase if made before 2017.
2. Engine model found on ID plate
3. Date of manufacture found on the left side ID plate.


Note: This is a “DIY” Do it Yourself Kit: The End User or the Installer becomes the vehicle manufacture and assumes all laws of the land including any product liability. Do not use or buy this product if you expect otherwise. Mechanical aptitude and working ability is required to perform this installation. Many “do it yourself” backyard mechanics will find this project rewarding. A love of small engines is the only required catalyst for this project. However, installation is sometimes best done by a professional auto or motorcycle mechanic. WARNING: Do not use a donor bike with front and rear fenders as side struts can come loose and lodge in wheel spokes causing danger to rider. Frame size should have a 70 degree included V angle with down-tube of 28 to 42mm dia. and seat tube of 28 to 34mm dia. For sufficient engine clearance select a bike with a seat tube length of at least 12 ½ inches measured between bottom of top tube and top of pedal sprocket tube. Using a bike coaster brake only is not recommended as chain can break leaving no brake at all. Use a bike with front and rear brakes to ensure best stopping ability; Remember, a quality installation and daily maintenance is paramount to safe usage and long term satisfaction. You may find many uses for this engine such as power for a stationary machine or for other off road machines. Have fun and good luck on your motorized project. Happy trails to you from GruBee / China GAS and YD:

STEP #1 Mounting the Engine:

1. The engine mounts in a “Vee” frame. It is best to make sure all 4 engine studs are securely bottomed out in the engine before mounting. Use a double nut “Jam Nut” procedure to tighten. Later model engines have the 2 front M6 x 50 studs with Allen heads for tightening purpose.
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 frame tubes exceeds the engine mounting span then additional spacers or welded brackets may be required. Mount the engine to the seat tube first and then fit to the front tube. If frame tube fit is smaller than engine clamp dia. use hard rubber shims to make fit securely.
Step #1. Install engine on seat tube first: Your engine will fit front down tubes from 28 to 40mm dia. See figure 1. below for an example an installation on a bike with bigger tube than 40mm....
4. If the seat post tube is too small to fit the rear engine mount, a use shims from GruBee shim kit found at
Your Engine needs to have the carburetor set in a level position. Too much engine tilt can cause chain to hit the drive cover and engine to not run correctly. It is best to have the drive chain to rear wheel sprocket be as horizontal as possible with no more than 15 degrees max engine tilt. After the desired engine location is determined mount the engine to frame. Appling LocTite thread lock is recommended to avoid loosening due to vibration. Note: All threads are metric.
Rubber wrap should also be used to isolate the rear mount on the seat tube if an alum. frame is used.
Mount your engine as low as possible in the frame with the chain top side horizontal as possible:

Chain Wheel Sprocket Installation:

   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
1. For kit sprocket installation, locate sprocket on axel hub with curved side next to spokes, shinny side in.
If not pre sliced, cut the rubber isolator ring between holes in order to fit INSIDE the spokes and around the axle. Install the split steel retainer plates next to the rubber isolator and insert 9 bolts.
2. 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.
3. The Chain Sprocket on the Wheel must align within 1/2 cm to the Chain Sprocket on the Engine.
4. The wheel chain sprocket is mounted with teeth-out and dish-in next to spokes. SEE FIG. #2
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.
A. Remove left rear cover plate from engine. This is the plate next to and under the clutch swing arm.
B Your engine may come with a standard bike chain or with a Heavy Duty 415 chain depending on how it was ordered by your dealer. Engine drive sprockets are different depending on chain size. The 415 chain uses a wide drive sprocket and the std. bike chain uses a narrow one. A 415 chain will work with a narrow sprocket but a std. bike chain will not go over a wide drive sprocket. Note: Install chain with master link clip on outboard side of the primary drive sprocket teeth. ( Note: wide tires larger than 2.125 may rub on a wide 415HD chain: )

C. 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.

D. Fit chain, measure and remove excess links to assure proper length. Be sure master link connection rides on the inboard side of the primary drive sprocket or interference of link and sprocket can occur. Proper chain length is when top chain has ¼ inch to ½” deflection with the bottom side of the chain loop tight.

E. Chain tension adjustments can be made by pulling rear wheel back if frame has straight slot wheel drop out. If both chains can be adjusted equally then installing chain idler on the wheel strut may not be necessary. At installer’s discretion the chain idler can be installed on either the pedal chain or engine drive chain.

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

Ignition Coil and Engine Kill Switch installation

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

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

C) Install Engine Kill Switch Wire on throttle to white wire coming from engine. Install the other wire with eyelet to a good frame ground not on paint. This will ground ignition and stop the engine when the kill button switch is activated.

D) Route all wires away from engine exhaust heat. Secure wires with a plastic tie straps.
*!WARNING! Operation of engine without a stop or kill switch 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.
Warning: In order to maintain engine warranty and to stay within engine emission standards set forth by EPA do not exchange muffler or carburetor to a non- compliant replacement. Replace with original OEM SkyHawk parts only.


Clutch cable installation and adjustment:

A) Install clutch lever to left side of handlebar and attach cable end barrel into lever slot hole.

B) 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.

C) 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 arm. Handlebar clutch lever must be in the released or outward position to complete this operation.

D) Activate lever a few times, and check clutch arm for slight free play: About 1/16” engine clutch arm free play is required with the handle bar lever in the released in what is called clutch engaged position or the engine will fail to start if cable is too loose or if too tight. Re-adjust as required.

E) Basics of clutch operation: The handlebar lever pulls the cable that moves the engine clutch arm. In turn the clutch arm pushes a rod through the motor that pushes the clutch plate out. ( similar to a car clutch.) Releasing the handle bar lever engages the clutch and provides engine torque to the drive chain or to start the engine. The clutch friction allows engine to start, and also transmits 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 #4.

Carburetor and Throttle Installation

Install TCI module on down tube as far away from engine heat as possible.

Note: A TCI ignition module is not the same thing as a CDI ignition module…

1. First install Blue & Black wires from engine magneto to same color TCI wires. TCI is transistor controlled and CDI is capacitor discharged and must use a 12V battery. Warning: Do not hook up wires backwards or damage will occur to the TCI.

2. Next install the throttle handle kill switch wires into the 2 remaining open holes of the 2 TCI wire terminals.

3. Push the clear rubber protectors over the twin connections and tape with black electrical tape.

4. The remaining white wire from the engine is not needed unless you want to run a small wattage 6V headlight but it’s not recommended as it will rob engine ignition power so is really best to tape this wire up securely or just snip it off at the engine exit plug.

5. To keep water out of the magneto box use a heat shrink tube over the wire sheathing and seal exit plug with RTV.
The “Magneto” is the heart of the ignition system and is controlled by the rotation of a permanent magnet rotor on the left side of the engine. When a N./ S. magnetic flux field rotates past the magneto coil an induced trigger voltage signal is sent to the TCI via blue / black wires so as to allow the TCI to fire the spark plug at the right time of 25° BTDC.
Engine firing timing is not adjustable; Position of p/m rotor is fixed to ensure correct timing.
If engine does not fire at start up check all connections. Check if kill switch has an unwanted ground. Make sure the magneto has a good ground and not insulated by varnish.
These engines conform to 2015 EPA Small Engine Spark Ignition emission regulation 40CFR1054 and if used on a bicycle the combined weight of this engine kit and bicycle cannot exceed 20kg. Failure to do so violates the 1970 Clean Air Act. To ensure your engine warranty always use our recommended oil. ECOTECH
Check out for an optional super high strength rotor magnet.
Use this procedure for attaching throttle cable to carburetor slide valve:
The small stop on the cable wire end slides through the long groove on the slide valve. Early slide valves were made of brass and later ones are made of black plastic.
( Note component positions in pictures; Needle clip is factory set in second slot and is not adjustable:)
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.
A) Install twist grip throttle on right side of handlebar end. On some handle bars it may be necessary to ream out the handle ID to fit the bar so that the throttle will twist freely. It never hurts to add a few drops of light wt. oil to let trickle down the cable inside the full length of sheathing.
B) After installing cable inside the carburetor you are ready to mount it on engine intake tube and tighten clamp screw. Mount engine so carburetor sets as level as possible.
1. Note: Factory Sealed Air /Fuel ratio screw. Factory set by turning adjustment screw to closed position and then opened ¾ turns outward or less than 1 full turn before it was sealed with epoxy.
2. Jet Needle: Carb. comes with clip set in position #2 from the top. Different positions may be required to make your engine run correctly depending on altitude above sea level and fuel economy desired. If a more rich gas mixture is required you can move the jet pin “pac man” clip to the next lower position notch.
Fuel Tank installation
A) Attach fuel petcock to tank. Use Teflon tape to seal threads. Careful not to strip threads.
B) Mount tank on bike top crossover frame with two supplied brackets and nuts.
C) Attach EPA Black rubber 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 screen as residue from the tank may have clogged the screen.. It is highly recommend that a tank liner coating be applied inside the tank before installation. This product is called Kreme and is available from motorcycle dealers;
IMPORTANT: PLEASE READ THIS: Gas and Oil Mixture Fuel ratio:
Your engine is a 2 cycle design, therefore, a gasoline/oil mixture is necessary. It is recommended that EcoTech brand synthetic oil be used which was used to pass EPA emission. During break-in period, (1st tank of fuel or 6 hrs ), the mix should be 25 parts gasoline to 1 part oil. After the break-in period, the ratio can be increased to 50 parts gasoline to 1 part oil if our recommended oil is used.
*NOTE: To ensure your engine warranty use ECOTECH Synthetic 2 Stroke Engine Oil. It can be purchased from your Skyhawk engine dealer if not found locally..
!WARNING! 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.
# 1. How to Adjust Clutch if signs of slipping or squealing are encountered :
A) Disengage clutch by pulling handle bar clutch lever inward and lock into catch lock.
B) Remove right side engine clutch cover and remove small locking screw on center *Clutch Adjust Nut.
C) Pull clutch arm on left rear engine inward. Back off *Clutch Adjust Nut ¼ turn counterclockwise.
D) 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 1/6” clutch arm free play.
E) Tighten *Clutch Adjust Nut on clutch plate clockwise until just snug.
F) Then re-install small locking screw in outer edge of *Clutch Adjust Nut .
G) Good idea to place a small gob of grease at gear mesh area. Use grease sparingly! Then replace cover.
H) Squirt light grade oil down clutch cable sheathing to reduce friction and make for easy lever pull.
2. Carburetor
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 and if that is not the problem check for a clogged up muffler.
#3. 3 pt. Spark Plug
Remove spark plug and inspect for excess carbon build up. Clean, re-gap to .0.036” of an inch if necessary. Check plug after every 20 hours of operation. New 3pt. spark plugs are available from your selling dealer. Be careful using aftermarket spark plugs as heat range and threads differ greatly. An extra plug is included in your kit: When replacing the spark plug it’s best to use a 3 point electrode spark plug P/N Z4JC to ensure total combustion. Can use the optional higher cost NKG B6HS spark plug. )
#4. Exhaust system
After 50 hours of operation check exhaust pipe for excessive oil and carbon build-up. If muffler is clogged your dealer has a replacement. Make sure attaching nuts are tight and no exhaust leaks are occurring. Be sure to use supplied support strap to secure exhaust muffler to a solid anchor point on bike frame or engine.
A) To remove inside catalytic exhaust insert loosen the retaining screw on end cap and remove.
B) Pull cap and baffle out of pipe. Note: Some catalytic inserts are welded in and cannot be removed. If you need a replacement muffler contact your dealer. Muffler has an air shield welded on the outside of muffler again per EPA test rulings. This insures a hot run so catalysis can better clean the exhaust.
C) Clean with degreaser, rinse and dry. Re-assemble: File muffler attach flange to have smooth flat surface.
D) Always use a new exhasut gasket and good idea to use double nuts on muffler attach studs;
*NOTE: Excessive periods of low speed operation, idling or leaving fuel petcock in the “on” position during shut down periods may cause the muffler to become clogged with unburned fuel.
#5. Drive Chain: size: 415
Every time bike is ridden check the tension of the drive chain by:
A) Rolling to bicycle forward to remove slack from the bottom of the chain.
B) Find the center and push downward on the top of chain while measuring the deflection.
C) 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 10 ft/lb 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 sprocket and also in cover hole. This will also help reduce 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 & wear a helmet.
IMPORTANT: PLEASE READ THIS: Gas and Oil Mixture for Fuel ratio
The engine is a 2 cycle design, therefore, a gasoline/oil mixture is necessary. It is recommended that EcoTech brand synthetic oil be used at a 50 to 1 ratio but only after engine break in has been accomplished. During the break-in period, (1st tank of fuel or 6 hrs ), the mix should be 25 parts gasoline to 1 part oil. After the break-in period, the ratio can be increased to 50 parts gasoline to 1 part 2 cycle synthetic oil.
!WARNING! Remember safety first: Wipe up any spilled fuel. NEVER fuel a hot engine or light a cigarette 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.
Step #1. After filling tank with the correct oil/gas mix open the tank fuel valve. Fuel line is in the open position when the small lever is pointed down. Move choke lever to the on position. This is the small lever at the end of the choke cable All the way Up the choke is on. All the way Down the choke is off. Move progressively downward to off position during engine warm up period.
Engine Starting procedure for Lever Clutch Models:
1. Pull the handlebar clutch lever inward, to disengage the engine from the rear wheel.
2. Pedal; (down hill if possible for first start)
3. A mid frame or rear wheel bike stand is helpful to start the engine in place.
4. Let out the clutch lever all the way out and continuing to pedal. The result is a direct engine hook up via the friction clutch with the rear wheel via chain and sprocket. The engine will now start spinning, Pedal until motor starts. Accelerate slowly at first..
5. Twist throttle to increase speed, reverse twist throttle to decrease speed. To stop,
disengage clutch and apply brakes. To accelerate, pedal and release clutch while opening throttle.
6. Adjust choke to the smoothest engine running position.
7. After warm up push choke lever all the way down. If engine races too fast, or too slow, pull clutch lever and lock in the notched catch, stop and adjust engine rpm.
8. If the rpm needs adjusting, turn the idle adjust screw (left side of carburetor) in or out slowly to obtain the proper idle speed of about 1400 rpm +/- 100 rpm. To correctly break the engine in, Do not exceed 15 mph or 30 min. continual running for the first 50 miles during engine brake in. Engine will have 15 to 20% more power after break in.
9. To stop the engine, push Kill switch and turn off gas valve at tank. Turning off the gas will prevent fuel from being siphoned from tank. Warning Note: Never leave the tank gas valve in “open” position” when engine is not running or the bike is in storage.
10. After or before each ride check all mounting fasteners, including hd. Bolts, axle and brakes.
11. Warning Note: Engine lock up or piston seizure due to improper gas / oil mixture will not be covered by factory warranty. This the responsibility of the owner / operator to make sure the gas and oil is mixed correctly. It is recommended that a temp gauge be installed on the handlebar sensing off an engine head bolt. Should the engine temp. approach 250C let idle for 1 minute and shut off to cool. Shutting off an engine that was running too hot can seize the piston to the cylinder wall.
Proper use and maintenance is required for the continued enjoyment of your Bike Engine. This product has been manufactured to strict quality control standards. For product warranty policy contact your selling dealer. Warranty approval is subject to dealer inspection and only the defective part or parts will be replaced, not the complete kit or engine. Only the defective part or parts should be returned to the selling dealer for warranty replacement consideration. Your dealer may require you to obtain his authorization first before returning defective parts. Include description and picture of failure with as many details as possible. Note: Seized pistons due to improper gas / oil mix or shipping damage due to carrier neglect is not warranty. Using gas with more than 10% ethanol causing engine to run hot and seize up is not warranty. Using inferior oil can cause engine failure and is not covered by warranty. Using EcoTech oil will ensure your warranty. Hooking up TCI wires backwards causing a failure is not warranty! Observe color code when installing these wires from engine to the ignition module. Work sober and ride safe.
When replacing the spark plug in an Angle Fire head it’s best to use a 3 point electrode spark plug P/N Z4JC to ensure total combustion. ( Can use the optional higher cost NKG B6HS spark plug. )