Yamaha dt125 was fine a few weeks ago but when i have since tried to start it . it does not start unless plug is taken out and fuel is cleaned off and then it starts but cuts out soon after

SOURCE: fuel for yamaha dt 125

This bike uses unleaded gasoline. At only 6.7 to 1 compression you can use the lowest octane fuel you can find. 87 in the US is what that would be around here, but across the pond the octane numbers are different. But don't forget the two stroke oil. That may be more expensive than your fuel cost.

SOURCE: 1986 yamaha big wheel 80

I believe the spark is too week, high tension sparks should be crisp fat and blue with a hint of orange, a weak spark could be the result of a faulty ignition generator or coil, sometimes the spark is controlled by a Capacitor, when these break down the spark will be out of 'Kilter' the Yeti... also check main and starting jets as well as any fuel diagrahms, good luck the YETI

SOURCE: Strange thigs about YAMAHA TW 125

Hi
I have been working on my carb today,the pipe from the bottom of the carb should just run down by the bottom of the swinging arm,there should be another pipe from the pipe on the left side of the carb just above the fuel intake which also runs down to the swinging arm and connect to nothing.
Cheers

SOURCE: 1989 tw200 yamaha won't start

G'day egdbcs . Ok.now lets see.You say good spark,so i'm presuming you are doing the old sight test.Try bending the arm on a know good sparkplug about 5-6mm,earth the plug and kick'er in the guts(crank it over)Be very carefull , high voltage danger.If there's still a good spark it's safe to say that there will also be a good spark under pressure in the combustion chamber,speaking of which you should also do a compression test,anything over 100psi should be ok. as i'm not to sure of the extent of the re-build,hopefully the valves were lapped and checked for straight and true and valve seals replaced,if you notice oil on the tip of the spark plug you could have a leaking valve seal or oil seal .Try putting a small amount of fuel directly into the combustion chamber ,tighten up the spark plug ,install the plug cap and.......Yeah ..You guessed it ..."kicker in the guts".If all the abouve are correct and true it should fire up.If it runs for 5-10 seconds then stops you've got some sort of fuel starvation problem , could be dirt in the carb,blocked idle jet ,or air passage or even the needle could have come off it's clip,believe me with an old bike like yours anything could be worn and loose inside that carby.The only other thing to consider is the timing.There may be a good spark but is it happening at the right time inside the engine???. I'll leave it all in your capable hands EGDBCS.Hope this helps to solving your worries. Chow for now......Tilleydog..

SOURCE: yamaha big bear 400 will

Sounds like a problem with the starter, could be a starter fuse, relay or solenoid. The start cicuit wiring could also be damaged. If you can pull-start the motor, and it runs fine, you have pretty much eliminated any problems with the motor. Check the wires running from the start button make sure they are intact, also trace them and look for around a 1" cubed black box. This is the relay, when you push the button, if its working, you will feel the box click. Also locate the starter and do the same thing. If you feel or hear the starter click, the solenoid is working. The battery voltage could also be too low to energize the starter motor. Could also be a battery or alternator issue. Check the battery voltage and for any sounds coming from the bike when you push the start button.