Skyhawk Instructions


Rev. Aug 4 2015

2015 SkyHawk GT5A EPA Certified Gas Engine

  • 2 stroke gasoline / oil mix, friction clutch. air cooled engine

  • 66cc 47mm bore x 38mm stroke 1.7Kw @ 6000 rpm

  • Catalytic muffler; CDI ign. module, EPA certified fuel line

  • Special PE14 NT non-adjustable air fuel mixture carburetor

    • Gt5A has up to 32mm dia. tube attachment at rear and up to 43mm dia. at front.

    • To fit on smaller tubes use shims to downsize:

    Step #1. Record the following information and save for warranty purposes and for future repair service.
    1. Record; Engine serial number found on the right side front of the engine crankcase,
    2. Record: Engine model and Date of manufacture found on the left side metal ID plate next to the EPA sticker;
    Note: This engine has no OEM application nor is it intended to be used for any OEM engine replacement. It is intended for “DIY” ( Do it Yourself ) individual hobbyist applications with certain restrictions applicable to EPA regulations: The “End User” or the “Installer” becomes the vehicle manufacture and assumes all laws of the land including any product liability in constructing any vehicle suitable for carrying a human being.. Do not use or buy this product if you expect otherwise. Mechanical aptitude and small engine knowledge are both required to perform a working and safe installation.

    Any repair shop or person of the owner's choosing may maintain, or repair this engine, however to maintain emissions warranty and engine efficiency use only a Skyhawk E`2A-EPA Catalytic muffler replacement after 50hrs. usage and use only Z4JC spark plugs. For carburetor repair use only genuine SkyHawk PE14 service parts. Use only EPA certified fuel lines such as the E-23A fuel line included with this engine.

    This engine meets the 2015 EPA Small Engine Spark Ignition emission regulation 40CFR1054 and is designed for 50 hrs. exhaust emission compliance. If used on a bicycle for power assist the combined weight of engine and the donor bicycle cannot exceed 20kg. Failure to do so violates the 1970 Clean Air Act. If used on hand held or stationary power equipment said weight limits do not apply. Your state, country or city may have additional rules for application and usage of this engine.

    Remember, a quality installation, correct oil fuel mix and daily maintenance is paramount to safe usage and long term satisfaction. You may find many uses for this engine besides just on a bicycle such as power for a stationary machine or for other off road machine application. Have fun and good luck on your motorized project. Happy trails to you;

    Mounting the Engine:

    1. The engine mounts best in a “Vee” type frame with a 70 degree included angle. It is a good idea to make sure all 4 engine mounting studs are securely bottomed out in the engine before mounting. Use a double nut “Jam Nut” procedure to tighten. The front mounting studs are M8 and have Allen heads for easy of tightening and removal. If mounting your engine on a flat V surface you will want to use Rubber Isolation Blocks that are available from your dealer. P/n RB43 for front and P/n RB32 for rear. See Fig #2. Gt5A engines have a front mount that can fit tubes 40mm to 50mm in dia. and up to 34mm dia at the rear mount. Too much engine tilt can cause the drive chain to hit the drive cover as well as carburetor float malfunction. It is best to have the drive chain going to the driven sprocket 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 so the carburetor is in a true vertical upright position. Appling LocTite thread lock is recommended to avoid loosening due to vibration. Note: All threads are metric.
    2. Remove left rear cover plate from engine. This is the plate next to and under the clutch swing arm.
    3 The engine 10T drive sprocket accepts 410 chain ( std. 3/8-1/2 Bike chain: or 415 chain.
    (a) A special wide 10T sprocket made specifically for a 415 HD chain is available from your dealer.
    4. Use the supplied spark-plug wrench to turn engine sprocket to feed chain around it.
    5. 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.
    6. Mount CDI ignition module, close enough to attach coil wire to spark plug. Mount as far away from exhaust pipe as possible to avoid heat damage to semiconductors.
    7. Attach CDI wires to same identical color coded wires coming from engine magneto.
    8. Install the 2 Engine Kill Switch Wires to the empty terminals on the CDI / magneto wire connections.. Honoring color code not important. This will stop the engine when the kill button is pushed.
    9. Route all wires away from engine exhaust heat. Secure wires with a plastic tie straps.
    *!WARNING! Operation of this 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 engine at slowest idle speed while applying a driven wheel brake.
    In order to maintain engine warranty and to stay within engine emission standards set forth by EPA do not change the catalytic muffler or carburetor to a non- compliant replacement. Replace with original OEM SkyHawk parts only. If available using Eco-Tech 2 cycle oil is also recommended.
    Clutch cable installation and adjustment:
    A) Install a stainless steel clutch cable lead barrel end into lever slot hole.
    B) Squirt light oil down the cable sleeve: Route clutch cable through the ball-mount on engine 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 with clutch lever in the released position. Activate hand lever a few times, and check clutch arm for slight free play: About 1/16” engine clutch arm free play is required with the clutch 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.
    D) Basics of clutch operation: The hand lever pulls the cable that moves the engine clutch arm. In turn the clutch arm pushes a rod that pushes the clutch plate out. ( similar to a car clutch.) Releasing the hand lever engages the clutch and provides engine torque to the drive chain or to start the engine. The clutch friction allows engine to start when the driven wheel is rotated and also transmits engine torque to the drive chain.
    Figure #4 If Clutch cable is not adjusted correctly the engine will not start. Check for slight clutch cable arm free play with handle bar lever released which would be the clutch engaged position.
    Be sure to check all nuts and bolts on Engine and end of muffler for proper tightness.
    Mount the CDI ignition module P/n B-54 as far away from engine heat as possible.
    1. Honor color code when installing Blue & Black wires from engine magneto to same color CDI wires. Warning: Do not hook up wires backwards or you will possibly damage the CDI module.
    2. Install 2 kill switch wires into the 2 remaining open holes of the CDI wire terminals.
    3. Push the clear rubber protectors over the twin connections and tape with black electrical tape or apply heat shrink tubes. 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” P/n B-45 is the heart of the ignition system and is activated by rotation of a permanent magnet rotor. When a N/S magnetic flux field rotates past the magneto coil an induced voltage is sent to the CDI via blue / black wires so the spark plug can fire
    Engine spark timing is not adjustable; The magnetic rotor position is keyed to the shaft to ensure correct 25 degree BTDC timing. If engine does not fire at startup check all connections. Check the kill switch for an unwanted ground. Check magneto frame’s path to ground.

    If installing this engine on a bicycle, EPA requires that the total combined vehicle weight with engine and accoutrements cannot exceed 20kg. Failure to meet this weight requirement means you are in violation of the 1970 Clean Air Act so stated at
    Here is an example of an Aluminum 700c bike that allows total weight to be less than 20Kg.
    Use this procedure for attaching throttle cable to carburetor slide valve:
    Insert the cable end with stop plug in the long grove slot on the slide valve with plug seated on the down or inboard side. Beware: there are 2 different NT Carbs. The best one to use for off road racing is the NT carb with a 14.95mm in dia. slide valve identified by a fuel shut off valve and the word SPEED on the carb body. However, to meet our engine’s EPA exhaust emission standards we must use a special modified P/n PE14 NT carburetor with a smaller 14.4mm slide valve and special jetting. Be sure to check air cleaner attach screws and choke lever nut for tightness before installing on the engine. Air cleaner screws and or nuts coming loose and entering the engine causing failure is not covered by warranty.
    The pac-man clip on the needle of a PE14 NT carb is factory set and is not adjustable: A spring is placed inside the slide valve tube and seats on top the bright silver plated pac-man clip that is on top of the needle pac-man clip so when the throttle is twisted spring compression allows the slide valve with needle to return when the throttle is released. For this to work properly the throttle handle must twist freely in both directions prior to the cable being installed. It never hurts to add a few drops of light wt. oil to let trickle down the cable inside the full length of sheathing. After installing cable inside the carburetor you are ready to mount it on the engine intake tube and tighten clamp screw. Mount engine so carburetor sets as level as possible in a vertical position.

    Throttle installation;

    Twist grip throttle with kill switch

    Twist Throttle with lever that can control 2 brake cables.

    Thumb operated lever throttle.


    Fuel Tank installation

    A) If engine is to be installed on a bicycle a steel tank must be used with a EPA approved fuel line. Many metal fuel tanks are available including mid frame tanks and over the rear wheel tanks are available.

    If the engine is to be used as stationary power other tank choices may be available.


    If installed on a bicycle EPA requires that the combined total weight of the vehicle with engine and accoutrements cannot exceed 20kg. This means you are limited to using only light wt. aluminum frame bikes that weight under 10kg to ensure you do not violate the Clean Air Act of 1970. Contact EPA’s Office of Transportation and Air Quality for equipment certification requirements under 40CFR-part 1060 rules.


    IMPORTANT: PLEASE READ THIS: Gas and Oil Mixture Fuel Ratio:

    Engine break in or wear–in is most important; The engine is an oil/mix 2 cycle design, therefore, a gasoline / oil mixture is necessary. A synthetic oil can be used at a 50 to 1 ratio if rated Iso-L-EGD / JASO-FD but only after engine break in has been accomplished. During the 1st gas tank break-in period, the mix should be 25 parts gasoline to 1 part oil. After the break-in period, the ratio can increased to 50 parts gasoline to 1 part oil. *NOTE: The recommended oil to ensure your engine warranty is ECOTECH Synthetic 2 Stroke Engine Oil but if not available you can use other brand names as long as it is of the same rating. Usage of non approved oil can void your engine warranty. Do not use E-85 fuel. Remember safety first: Wipe up any spilled fuel. NEVER fuel a hot engine or smoke while fueling.


    # 1. How to Adjust Engine Clutch if signs of slipping or squealing are encountered:
    A)  Engage clutch by releasing handle bar clutch lever from the pin lock position.
    B)  Remove right side engine clutch cover and remove small locking screw on center *Clutch Adjust Nut.
    C)  Pull clutch arm on left rear of engine inward. Back off *Clutch Adjust Nut ¼ turn counter-clockwise.
    D)  Release said engine clutch arm and check arm for 1/16” free-play.
    E)  Readjust *Clutch Adjust Nut as required to get the required 1/16” clutch arm free play.
    F)  Tighten *Clutch Adjust Nut on clutch plate clockwise until just snug.
    G)  Then re-install small locking screw in outer edge of *Clutch Adjust Nut .
    H)  Good idea to place a small gob of grease at gear mesh area. Use grease sparingly! Then replace cover.
    I)   Squirt light grade oil down clutch cable sheathing to reduce friction and make for easy lever pull.
    #2. PE14 Carburetor Critical Emission related maintenance
    Idle speed adjustment is the only screw on the carburetor. Setting idle speed is up to the end user to determine that best suits his engine operation. Normally 1800 to 2200 rpm is the idle range used. Depending on dusty riding conditions, clean the 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 muffler. If engine is to be left setting for long periods of time, like over the winter months, be sure to drain the carb so gumming does not occur while in storage.
    #3. Z4JC 3 pt. Spark Plug Critical Emission related maintenance
    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. When replacing the spark plug use an original 3 point electrode spark plug P/n Z4JC to ensure total combustion and efficiency.
    #4. E-12A-EPA Exhaust system: Critical Emission related maintenance
    After 50 hours of operation replace the catalytic muffler with a genuine Skyhawk EPA muffler P/n E-12AEPA. Make sure attaching nuts are tight and no exhaust leaks have occurred. Be sure to use a support strap to secure exhaust muffler to a solid anchor point. Note: Muffler catalytic insert is welded in place and cannot be removed. If you need a replacement muffler contact your dealer. The Cat Muffler has an air shield welded on the outside as per EPA test rulings. Scrape old muffler in accordance with environmental regulations.
    A) Always use a new exhaust gasket and it’s 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 and affect engine performance.
    #5. Drive Chain: The 10T drive sprocket will accept both 415 and standard bicycle chain.
    Push downward on chain at center span. Tighten chain if deflection is more than ½ inch.
    #6. Head Bolts: Critical Emission related maintenance
    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 as head bolts can be damaged. Stripped 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 excess may adversely affect clutch operation.
    #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.

    Instructions for Drive Sprocket & Crankshaft Gear Puller.

    To remove 10T drive sprocket secure sprocket from moving and remove nut.
    Screw puller tool
    into the sprocket ID threads.
    Tighten puller tool securely;
    Hold tool with end wrench while using ratchet on tool bolt to push on the output shaft which causes the sprocket to lift off the shaft.
    To remove engine B5 gear;    Secure clutch gear and remove slot head screw;      Remove star washer;
    Reverse bolt in puller tool;     Secure tool in output gear;    Hold tool with end wrench and ratchet bolt CW.



    IMPORTANT: PLEASE READ THIS: Gas and Oil Mixture for Fuel ratio

    The engine manufacture recommends 100% pure gasoline, No more than 10% ethanol is OK but never use E-85 fuel. The engine is a 2 cycle design, therefore, a gasoline / oil mixture is necessary. It is recommended that EcoTech brand synthetic oil if available in your area 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 increased to 50 parts gasoline to 1 part 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 Lever Up > the choke is on. Lever 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 clutch lever inward, to disengage the engine from drive line..
    2. If on a bicycle pedal fast and release clutch lever. This will crank the engine for starting.
    3. An optional rope pull system can be installed on the left side of the engine if not on a bicycle.
    4. Twist throttle to increase speed, reverse twist throttle to decrease speed.
    5. Choke lever up is on: Keep adjusting choke to the smoothest engine running position until full off.
    6. After warm up push choke lever all the way down. If engine races too fast, or too slow, pull clutch lever to locked disengage position and adjust engine rpm screw to no more than 2300 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 1800 rpm to 2200rpm +/- 100 rpm
    • Run at no more than ½ to ¾ open throttle for first 2 to 4 hours to break the engine in slowly..
    • Engine will have 15 to 20% more power after break in.
    9. To stop the engine, push Kill switch and turn gas valve off 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 when the bike is in storage.
    10. 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. DO NOT E-85 fuel or use fuel with more than 5 to 10% ethanol.
    It is recommended that a temperature gauge sensing off an engine head bolt be applied to your project. Should the engine approach 250C let idle for one minute and then kill engine to it let cool. Suddenly shutting off an air cooled aluminum cylinder engine that has ran too hot past the 270C red line can seize or weld an alum. piston to the aluminum cylinder wall and destroy the engine which is not warranty:

    YuanDong SkyHawk mfg. > ENGINE WARRANTY POLICY:

    Proper use and maintenance is required for the continued enjoyment of your Skyhawk Engine. It has been manufactured to strict quality control standards. Basic engine warranty is 90 days however, the emission system carries an additional warranty. For the Emission System warranty policy contact your selling dealer. Warranty approval is subject to warranty station 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 engine serial # mfg. date and description of failure along with a picture and as many details as possible. Note: Seized pistons due to improper gas / oil mix or shipping damage due to carrier neglect is not warranty. Modifying the engine with a high compression head or by using other than the E-12A muffler and PE14 carb that was included with your engine will void your factory warranty. Using E-85 gas with gas with more than 10% ethanol causing your engine to run hot and seize up is not warranty. Attaching CDI wires backwards causing a failure is not warranty! Observe color code when installing these wires.

    Use EcoTech oil or equivalent rated Iso-L-EGD / JASO-FD to ensure engine warranty.


    When replacing the spark plug use a 3 point electrode spark plug P/n Z4JC to ensure total combustion.

    GOOD IDEA: Before starting engine the first time remove spark plug and use a squirt can to apply a few squirts of 10W engine oil on the sides of the cylinder wall, then spin the engine over a dozen times to pre-lub the piston / cyl. wall surface.. No need to remove the threaded brass nut on the spark plug as the 2015 design CDI wire terminal with soft cap will fit right over it OK. Not like earlier made engines.
    Part Number Service Parts Description -
    Contact your dealer for min order requirements:
    Z4JC Spark plug Z4JC M4X1.25 3 pt. Critical Emission related maintenance
    A-2-66 -Sq. AF Angle Fire Head
    B-Keys Complete assortment of all Keys for GT5A & Gt5
    A-#30-80cc Gasket kit includes all gaskets for GT5A & Gt5
    A-#32H-66cc Piston kit 47mm dia. piston, rings, pin & 2 clips
    A-#36-66Gt5ACFB Total Cylinder kit with piston and head
    B-2 Clutch Gear Cover
    B-3 Slot head Bolt- Crank Shaft output gear attach CCW threads
    B-5 Crankshaft output small bevel gear right side of engine.
    B-6-202 Oil Seal - wide for 6202 brg. Right side of engine only
    B-10 Rear Mt. block 35mm opening
    B-11A REAR Mt. hasp clamp steel for Gt5A 35mm opening
    B-11B FRONT Mt. hasp clamp steel for Gt5A 40mm opening
    B-16-202 6202-P Bearing Crankshaft sealed one side.
    B18,19,26,30-c Crankshaft assy. for 66cc Gt5 & Gt5A
    B-26-80cc kit Connecting rod with 2 needle brgs. for Gt5 & Gt5A
    B-27NB Needle bearing for piston pin 12.3mm long Fits all Skyhawk engines.
    B-28 Crank shaft pin > all SkyHawk engines
    B-29 Needle Bearing for crankshaft > all SkyHawk engines
    B-32-rd Grommet for coil wire Black
    B-40 Magneto cover
    B-45 Magneto Coil on horse shoe lamination stack Critical Emission related maintenance
    B-46-202 Oil seal Left side engine next to Magneto
    B-46 PL-66cc Tin Retainer plate for B-46 oil seal. Fits under magneto
    B-46-202 Oil seal on right side of engine
    B-48 Nut M8 x 1 - rotor
    B-49 Magneto Rotor magnetized Critical Emission related maintenance
    B-53 Drive Sprocket Cover
    B-54 CDI - ignition Module with spark plug wire Critical Emission related maintenance
    B56B Spark plug wire terminal cap; All engines Critical Emission related maintenance
    Gt5 - HW kit All engine fasteners for Gt5 & Gt5A engines. Allen head grade 8.8 high quality.
    PE14 PE14 EPA Compliant NT Carburetor, Non-adjustable ( small slide barrel 14.4 mm Ø )
    CK-19A Service repair kit for PE14 carb.
    C-#19B NT Carburetor, black AC ( large slide barrel 14.95 mm Ø ) for high performance.
    C-32A Boss Air intake pipe Alum. Fits 40mm stud spacing;
    E-12A EPA Catalytic Exhaust Muffler Critical Emission related maintenance
    E-23A EPA certified fuel line with 2 clips Critical Emission related maintenance
    D-#1A TOTAL Clutch repair kit. Includes all parts to completely rebuild clutch assembly.
    EcoTech oil 3.2FL OZ of high grade 2 cycle Synthetic oil mix. Meets warranty requirements