Question about Pit Bike 125cc 4 Stroke Dirt Bike

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Got spark compression and gas but bike wont start!

I bought this bike off a friend for 100 bucks it ran good but he had broken the Ignition Magneto so i bought another one hooked it all up and it has spark and compression but still doesn't start i took the plug out and put WD 40 in the plug hole put the plug back in but still wont start .. help please very frustrating

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Ckeck timmkng and vaulve clearance and flouts in carb

Posted on Jul 19, 2014

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You need three things,spark fuel compression you have two check for fuel

Posted on May 05, 2014

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Check to see if the ruin burton is on, if so out could be the switch isn't altering the connection to go the plug.

Posted on Dec 18, 2012

  • nicksgonefis
    nicksgonefis Dec 20, 2012

    what is the ruin Burton? cant say ive heard of it ? and thanks for answering :)

  • bo c lane
    bo c lane May 17, 2014

    bring number 1 cylinder tp top dead center then reposition magneto number 1 cylinder needs to be at tdc b4 installing magneto

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1 Answer

2004 yamaha yz250f ran all weekend then the next day after riding it, it wouldn't start


Hi, Alex and the usual suspects are:
1. Severely discharged or a damaged battery, should have 12.5 volts or better and be able to pass a load test if necessary.
2. 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.
3. Faulty main circuit breaker and or connections.
4. Faulty ignition coil and or connections.
5. Faulty spark plug, oil or gas fouled, wrong heat range or service type, wrong gap, loose in the cylinder head, broken electrode or insulator.
6. Faulty spark plug cables, leaking or broken, internal damage.
7. Faulty ignition module, switch, CKP, MAP, CMP, sensor and or any connector in the ignition circuit could have corroded, loose, or broken pins/sockets
8. Burnt exhaust valve or air leak in the exhaust system.
For more information about your issue and valuable "FREE" downloads that you will need please click on the links below. Good luck and have a nice day.
Bike won start just backfires occasionally
Dirt Rider Magazine
YAMAHA YZ250F Owner Service Manual
OEM parts for Yamaha
http://mybikemanuals.com/yamaha/yamaha-yz-owners-manuals

Apr 24, 2013 | 2004 Yamaha YZ 250 F

1 Answer

Troy built tiler won't start!!


What is the method your machine uses to decide when to fire the spark plug? Does it have a magneto, and/or ignition points under the flywheel, or a crankshaft postion sensor?

Apr 18, 2017 | Computers & Internet

2 Answers

1986 Honda CR80 quit running


C A R B U R E T O R .. have a qualified professional take a look at it....

your bike only needs THREE things to run,,(assuming the insides are good),,
1. A timed spark
2. Adequate compression
3. Proper fuel/air ratio

Start with one... eliminate one at a time until you find out which one is NOT happening!! (This is how a professional would trouble shoot your bike)!

Sep 24, 2017 | Honda Motorcycles

1 Answer

Changed fuel pump on 2003 flht ultra classic. Ran fine. Went to start bike couple months later now it wont start again. drained all gas put some cleaner and new gas in it. still nothing?


Hi Rustedwrench, when checking for spark the CKP needs to measure the compression bump in order to send the correct signal to the ICM/ECM so always check for spark with either a third plug grounded or lift the end of the plug boot 1/2 " off one of spark plugs that are in the head. and the usual suspects are:
1. Fuel tank empty
2. Fuel supply valve turned off.
3. Fouled spark plugs.
4. Engine flooded with gasoline as a result of over use of enrichner.
5. Fuel valve or filter clogged.
6. Vacuum hose to automatic fuel supply valve disconnected, leaking, or pinched.
7. Discharged battery, loose or broken battery connections.
8. Loose wire connection at coil, battery or plug between ignition sensor and module.
9. Spark plug cables in bad condition and shorting, spark plug cable connections loose,
or cables connected to wrong cylinders.
10. Ignition timing incorrect due to faulty ignition coil, ignition module, or sensors " Manifold Absolute Pressure" "Camshaft Position Sensor" "Crank Position Sensor" "Brake Apply Sensor
11. Engine lubricant to heavy ( winter operation )
12. Sticking or damaged valves or push rod wrong length.
13. Primary cam sproket spline sheared or missing spacer.
14. Security alarm system not disarming.
For a primary suspect please visit the website below: Good luck
Big Twin Carb EFI DTC Intructions codes Harley Davidson Forums Harley...

Sep 19, 2010 | 2003 Harley Davidson FLHTCUI Electra Glide...

4 Answers

My 1974 Yamaha 250 Enduro wont start I have cleaned and redone the carb. I have changed the coil pack and spark plug. Any suggestions will help Im not a mechanic by any means so not sure where to start...


you need good compression ( at least 90 psi , kicking it with the throttle open) , good crankshaft seals for sucking the fuel/air into the botton end, proper point gap and timing set for spark ( spark should be big and fat,if not the source coil is weak,, this is a flywheel magnito ignition and it needs no battery to fire the plug) if you clean the carb, make sure you also clean the choke pickup tube or it wont choke. also make sure you have the slide installed in the right direction ( not backwards and the idle is not set too high at first...compression/****-good spark at the right time-proper fuel/air ratio and it will run

Jul 04, 2010 | 1974 Yamaha DT 360

2 Answers

My son's bike just wont start. All of the normal


I can say i know nought about the model or any problems it may have. All i can say is to : 1 . check the compression and compare to specs. 2. Did they measure the output of the ignition high tension spark and did they make sure the spark had the correct timing??. 3.Ok ...there might be fuel getting to the carby but is that fuel getting to the combustion chamber. the engine is one big pump and it may have taken in some dreggs from the bottom of the fuel tank effecting or blocking jets and airways critical for starting.I would look at stripping the carb and giving it a clean out with compressed air ,hold the jets up to the light and you should be able to see daylight out the otherside.Another quick fix to see if it's a fuel problem is to remove the plug and fill the spark plug with fuel or dump about half a teaspoon of fuel in the combustion chamber,insert the plug and kick it in the guts.If it runs a bit then stops you've got a fuel supply problem.Once you have all these things 1.compression 2. spark 3. fuel. in the correct amount your engine should fire up......Hope i could give you some pointers on what to look for Thurstak......Good luck

Dec 07, 2009 | 2004 Gas Gas EC 450 FSE

1 Answer

Bike wont start


hi buddy to check the magneto just find the wires from the magneto and test them out with a volt metre if you have nothing there must be the stator plate gone get back to me buddy

Sep 20, 2009 | 1997 kawasaki ZX-7R

1 Answer

Not starting


piston rings gone on piston or a gasket blown take spark plug off and put a compression tester in the hole and check the pressure goes over 100psi if not its good bye to rings buddy

Aug 07, 2009 | Cycling

2 Answers

Motorcycles wont start


Your bike needs 4 things to run-Fuel, Spark, Air and Compression. One or some of these are missing.

1) Crank engine over several times to start. Remove spark plug. If plug is wet and smells like gas then it is getting fuel.

2) Check for spark
Put spark plug back into spark plug cap and lay spark end along side bolt or part of unpainted head making contact and crank over engine as if to start. If no spark then is electrical problem. Try changing spark plug. Check grounds. If not plug or grounds then purchase a shop manual from your local dealer and ohms test all electeical componet resistances as shop manual instructs. Be sure components do not meet specks before purchasing.

3) If has spark and plug was wet upon removal then gas has water or just old gas. If you drained the carb via bottom of carb screw into a clean clear container and see stuff at the bottom then carb is dirty with water and or dirt.

If your bike has been sitting along time condensation will build explaining water and or gas will loose its kick after sitting too long. If you think it has been sitting a long time it is best to dispose of old gas and refill with new. Water can also get into tank from gas can when fully tipped upright so dont dump every last drop into the tank...most ofter the last couple of cups are water.

If bike has been sitting for a few days and was running fine before that, turn off gas, drain carb via bottom of carb screw, close off screw and turn gas back on. This will refresh the gas in carb.

If none of these are the case and you have good fuel, good spark...check air filter for air flow. If all this is good then you need to do a compression check. A simple way to do it is to stick your finger in the spark plug hole and hold it in there with some force and have a friend try to start the bike. If it blows your finger out then it has compression. If it doesnt want to force your finger out then you have no compression and is a piston and ring problem. The only way to test compression for sure it to purchase a compression tester from auto parts store that has an adapter for your size plug hole and do a proper test. I hope this helps.

Apr 08, 2009 | 2002 Honda CR 125 R

1 Answer

2003 883 sportster wont start


What u are describing is typical of a faulty ignition system, but could also be a fuel problem. I check by removing the aircleaner and rotating the throttle. If u see a nice spray of fuel, thats probably not the problem. Check for a spark at the plugs. I can explain how if you need me to. If you cant see a good spark, U have an electrical problem. I had a crank position sensor go bad on me. Dont do what I did (replaced the battery, ignition, and regulator as part of my diagnosis procedure)

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