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Old 03-08-2010
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Keg Keg is offline
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Bike wont run - Diagnosis 101

After reading about Anth1978 bike problems I thought I would post up a basic couple of steps to check a bike that won't run.

There are three things that make a bike work - fuel, spark & air.

1) Air
Most bikes will run with a fully clogged air filter so air is rarely the problem.

2) Fuel
Pull the spark plug out and see if it is wet. If it is dry it will be most likely be a carby related problem. (If wet, try step 3 now) Drain the fuel bowl and try again.

If it only runs on choke or when you rev it, it is a blocked pilot jet or water. If it does not rev out it could be a blocked main jet, float problem or the clip of the needle could have come off.

If the bike stops after a couple of minutes it could be your fuel tank cap or breather tube being blocked. Try running with the cap slightly undone (be carefull). This is also a sign of a dying coil or other electrical thing too.

3) Spark
Put the spark plug against the motor with the lead on and kick it over fast. If you don't have spark it is electrical.

Don't worry if the spark seems weak or hard to see, I hear this complaint alot and 99% of the time it is not a problem. Modern ignition color is hard to see. If you are confident it is a problem hold your hand on the plug when kicking it over...WARNING it will hurt if it fires!

- Change the spark plug and re-test
- Disconnect the kill switch. Try looping the wires together also as some run open circuit to turn off.
- Check the coil is earthed properly and the other wires are also attached. Most Jap 4T bikes have the coil built into the lead so you can't do this.
- If you get it running, turn the bars from side to side. If it cuts out check the headlight wires. Disconnect everything and plug it back in, you will be surprised how fury inside some plugs can get.
- Check battery terminals by wiggling the cables. Tighten them.

I hope some of that helps without getting too involved in further steps. Some times a little bit of info is easier to understand than alot all at once.


Addition 7/5/11

- If the spark plug is dry in point 2) Check the fuel tank has fuel. Disconnect the hose from the tank off the carby and make sure fuel is flowing. You would not believe how many times I see this.
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Last edited by Keg; 07-05-2011 at 09:26 AM.
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Old 03-08-2010
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Top info Keg
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Old 03-08-2010
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Make this sticky, and can you do a bar pad version for my husky
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Old 03-08-2010
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I have made it a sticky. I will expand on the electrical side of stuff when I can, we might have to call it B.W.R. 102.
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Old 03-08-2010
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During any diagnosis I carry out, I check for fuel , spark , compression and timing.
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Old 03-08-2010
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my sons ttr50 wouldnt run , i checked the spark plug and it seamed to have good spark but still wouldnt run ,i put a new spark plug in it and it fired first go,
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Old 03-08-2010
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Spark has a good colour and a bad colour, normally it is a purple or blue colour and it can look very weak, when it is white it is normally no good or the plug is very wet.
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Old 03-08-2010
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Turn fuel tap on

Sorry had to be said

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Old 30-07-2011
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how about the spray can you can buy called start ya bastard , spray it in the carby intake and crank the engine see if it starts .
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Old 31-07-2011
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Quote:
Originally Posted by benk7659 View Post
how about the spray can you can buy called start ya bastard , spray it in the carby intake and crank the engine see if it starts .
If it starts with "Aerostart" or "start ya bastard" which are both just ether in an aerosol can it can point to 2 problems, 1: fuel obviously, a blocked jet or none in the bowl and 2: low compression, if there is definitely fuel getting through but it will only start with ether then it is likely got very low compression (usually from being dusted), the ether will burn no matter what.
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