Question about 2002 Yamaha TW 125

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How to start engine out of frame

I have eliminated the stock wiring harness from a 50cc pocket bike and need to wire coil directly to ignition. .

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Get some gas in the carb and opening the idle to the maximum. make sure the intake is clear. remove the battery is removed and kick it.

Posted on Jun 19, 2009


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Pocket Bike 50 will not start

Hi, Orlando and the usual suspects are:
1. Fuel tank empty.
2. The fuel tank has old dead gas.
3. Fuel tank bottom contaminated with ethanol sludge, dirt, water, rust, etc.
4. Fuel supply valve/petcock turned off.
5. Fouled spark plugs.
6. Engine flooded as a result of overuse of the choke.
7. Vacuum hose to the fuel supply valve/petcock disconnected, broken, cracked, or pinched.
8. Fuel valve/petcock or filter clogged.
9. Fuel line to carburetor or throttle body pinched, kinked or blocked.
10. Carburetor float stuck.
11. Fuel injectors clogged.
12. Fuel injectors stuck open.
13. Quick disconnect check ball stuck.
14. Compression below 75 PSI.
15. A stuck-bent-burnt valve.
16. Severely discharged or a damaged battery should have 12.5 volts or more and be able to pass a proper "LOAD" test if necessary, you may have a cursory reading of 12.5 volts or more but little or zero amperage the battery is faulty and must be replaced, AGM batteries fail in this scenario more so than lead-acid batteries.
17. Check battery terminals for damage or corrosion, check the battery cables at "BOTH" ends for loose, corroded, or broken connectors, "INSIDE" and outside the cable harness, perform connector wiggle test and check cables with an ohmmeter if necessary.
18. Loose or corroded wire connection at the coil or plug between ignition sensor and ECM module.
19. Spark plug cables in bad condition and shorting check for spark leakage in the dark, cable connections are loose or connected to the wrong cylinders.
20. Ignition timing incorrect due to a faulty ignition coil, ignition module or MAP, CMP, CKP, O2, TPS, ETP, IAC sensors.
21. Faulty neutral, clutch, kickstand safety switch.
22. Faulty fuel pump or fuse or relay.
23. Faulty or corroded run/stop switch.
24. Tilt sensor needs a reset.
25. Security system not disarming alarm needs a reset.
26. Check for engine trouble codes.
For more information about your issue and valuable "FREE" downloads that you will need for viewing or printing please click on the blue links below. Good luck and have a wonderful day.
Common Reasons Why My Pocket Bike Wont Start
Pocket Bike Won Start Help Quick Fix
GB Evolution F1 Pocket Bike Service Manual For Use And Maintenance
Coolster POCKET BIKE QG 40 User Manual
ACU Pocket Bikes Manuals

Btw, I’m available to help over the phone in case u need at

Dec 28, 2017 | RTO 47cc / 49cc Pocket Dirt Bike Atv...

1 Answer

Bike does not start

Hi Anonymous, and the usual suspects are:
1. Fuel tank empty.
2. Fuel supply valve/petcock turned off.
3. Fouled spark plugs.
4. Engine flooded as a result of over use of enrichner.
5. Vacuum hose to fuel supply valve/petcock disconnected, broken, cracked, or pinched.
6. Fuel valve/petcock or filter clogged.
7. Discharged battery, loose, corroded or broken battery terminal connections especially the "NEGATIVE" cable inside the harness at both ends.
8. Loose or corroded wire connection at the coil, battery or plug between ignition sensor and module.
9. Spark plug cables in bad condition and shorting, cable connections loose, or connected to the wrong cylinders.
10. Ignition timing incorrect due to faulty ignition coil, ignition module or sensors (MAP, CMP CKP and/or BAS).
11. Sticky or damaged valve or pushrod wrong length.
12. Primary cam sprocket spline sheared or missing spacer.
13. Security alarm needs a reset.
For more information about your issue, please visit the websites below. Good luck and have a nice day.
50cc Mopeds 125cc Scooters Motorcycles Motorbikes for Sale at AJS

Btw, I’m available to help over the phone in case u need at

Mar 02, 2014 | AJS Motorcycles

1 Answer


    • 1 Make sure the engine is completely cool. Disconnect the vehicle's negative battery cable.
    • 2 Remove any components that block access to the ignition coils in your vehicle. This can vary depending on the model, and there might not be any parts you need to remove. These parts can include the air duct intake, connections to the power steering pump fuel injector, harness connector, camshaft sensor, and engine wiring harness.
    • 3 Unplug the electrical connector to the ignition coil. Disconnect the spark plug wires from the coil, grasping the wire at the boot to disconnect it. Use a plug wire removal tool, if possible, and mark down each wire to remember which coil it connects to.
    • 4 Remove the mounting bolts to the ignition coil; a flare-nut wrench will help prevent stripping the bolts' edges. Remove the coil from its valve cover.
    • 5 Inspect the condition of the spark plug wire boot. Replace the wire if the boot is torn, cracked or deteriorated in any way. Coat the boot's interior with a silicone dielectric compound before reconnecting it.
    • 6 Insert the replacement ignition coil into the valve cover. Tighten the mounting bolts to the correct torque for your vehicle. It is usually small enough to be measured in inch pounds.
    • 7 Reconnect the spark plug wire and the electrical connector to the coil. Replace all parts that were removed or unplugged to reach the coils and connect the negative battery cable.

Jan 20, 2013 | Motorcycles

1 Answer

I have a 1984 harley sportster with a 3 wire sensor(white,black,and blue wires) that i need to hook up to my new dual fire ignition coil, and new barrel type key ignition. not sure where the wires for...

I can send you a complete wiring diagram for your Sportster. The wires you are talking about go to the stock igniton unit, the "brain box" or "black box" that is behind the triangular plate on the right side of the bike as best as I can remember (1984 was a long time ago). There should be two white wires on the coil and one is the "hot" wire and the other goes to the ignition unit. The pink wire goes to the tachometer. The blue wire goes to the opposite side of the coil from the white wire, same side as the pink wire. The black wire is a ground wire for the igntion unit most likely. But, I'm confused by you saying the wires go to a "sensor". The only sensor on the bike is in the timer cavity on the right side of the engine and the wires coming from it are different color from what you mention. Are you sure it's not simply a plug? Contact me directly at and I'll send you the diagram. Remind me of what you need.


Jul 25, 2011 | Harley Davidson XLS 1000 Motorcycles

1 Answer

Does the coil have to grounded to the engine block or just the engine bolted to frame ok for 47 cc pocket bike

coil needs to be grounded and make sure theres no paint at mounting points of motor to frame

Feb 22, 2011 | RTO 47cc / 49cc Pocket Dirt Bike Atv...

1 Answer

I have have a 2 stroke atv with no power to the coil , i cant work out why.

make sure the engine is grounded to the frame, check all wiring.could be your magneto has died

Dec 17, 2010 | RTO 47cc / 49cc Pocket Dirt Bike Atv...

1 Answer

I"m looking for a wirimg diagram for a custom aplication for a 1997 softail motor w/ electronic points placed into a ridgid frame useing a dyna coil.

The wiring for the ignition system is determined by the ignition unit that was used in the build of the bike. Remove the timer cover plate on the "nosecone" cover on the right side of the engine. The ignition unit is sometimes in that compartment. Let me know what is in there, i.e. Crane HI-4, and I'll either send you a wiring diagram or refer you to a website where you can get the wiring for it.

As for anything else to do with the wiring, all I have are a few "stock" wiring diagrams. If you bike is a custom build, the wiring is probably "custom" as well. I've seen custom build bikes with simple 8 wire wiring harnesses and then others have a full wiring harness for all sorts of gadgets on them. So, as far as a diagram is concerned, I'm pretty sure you're on you own on that. The builder should have made a diagram when he built the bike.

Find out what brand and model ignition unit your bike has and repost to me. We'll see if we can't get you going.

Good Luck

Oct 12, 2010 | Harley Davidson FLSTF - FLSTFI Fat Boy...

1 Answer

I have a black wire from a ignition coil not plugged in where does it go?

on the spark plug.if that is not it then it might be a earth cable that just gets bolted to the frame of your bike

Oct 12, 2010 | RTO 47cc / 49cc Pocket Dirt Bike Atv...

1 Answer

I have a John Deere 317 tractor that does not start. The engine turns but does not fire. The plugs and points are good. I do not get a spark at the points or plug. What should I check next next.

We will be testing for voltage to the points, coil, engine to tractor wiring harness, ignition switch

Tools needed:
volt meter to read 12 volts, or test light

1) with the points open: is there voltage at the connection wire at the points
If yes; adjust points to .020" and try to crank engine and check for spark
*** you may want to determine if condensor is connected to this wire also
if no
2) check point side (neg or - ) of coil for voltage
if yes, engine should start
if no
3) check for voltage at the + side of coil
If yes, coil is bad
if no
4) check wire connector from engine to frame wiring harness
if yes; engine should start

if no
5) check wiring on the back of ignition switch
if yes; engine should start

if no
6) check that ignition switch RED or BATTERY supply wire has voltage
if yes; switch is bad

if no
7) check supply wire and circuit breaker connected to the battery side of the solenoid
if yes; engine should start

if no; circuit breaker could be at fault or wire connector at battery supply

I’m happy to assist further over the phone at

Nov 08, 2009 | John Deere 420,1020,2010,2020,2510,2520...

1 Answer

I have a 2005 Harley Davidson engine in a custom built bike with stock wiring harness. New Crane cams fireball hi4tc ignition module and coil to match. New sensors bought directly from Harley dealer. I...

I would check the coil first and see if it needs replaced .If it's new and you still have reciept ,take and get a replacement coil for the one you bought and make sure your wires coming out of everything have power be tracing the system to see if there might be something shorting.

Apr 27, 2009 | 2005 Harley Davidson FLSTSC - FLSTSCI...

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