Yamaha SR250 weak spark so won't start

[grahambell]

Can anyone suggest what I should try next. With a spark tester it shows a weak but regular spark when I turn the engine over using the start button. If I replace the spark tester with a plug earthed onto the engine, I get a visible spark when I first press the start button. But whilst he engine is turning over, I get no further visible spark until I release the start button.
I have replaced the spark plug, lead, coil, ignition unit and pick up.
Regards

 

[seven54]

Only thing you haven't mentioned is your battery. Is it charged and in good condition? Are the terminals tight and free of oxidation?

 

[jay_kent]

+1

if you battery is even a little down on the juice everything will light up but as soon as you hit the starter the headlight will dim and it will be a no go. Charge it up and start from there.