cause of weak spark

[slopster]

My SRAD has been running slightly rougher then normal lately and lacking a bit of top end power and quite hard to start. Seems to run ok in the midrange. Checked the spark on all 4 cylinders yesterday and it is very weak. I can just barely see it. Sparkplugs looked ok but I replaced them anyway. I assume the coils are unlikely to be the problem because its highly unlikely that they would both go bad at the same time (they are fancy aftermarket ones and not very old by the way). I know the black box is ok because I had a spare and it doesn't make any differance. What should I be looking at as the cause of a weak spark?

[breakaway]

Battery? Earths?

[NinjaNanna]

leads gone high resistance???

[surfer]

Agree with Ninjananna and Breakaway - Check the battery voltage with a multimeter and charge if needed. Also replace the ht leads running to the spark plugs from the coils, and replace the end caps as these break down over time. If you say the coils are newish then it probably isn't worth replacing them.

Don't know what year your bike is. Do you have electronic ignition or is it points? If points then replce the condensors and check ignition timing. I suspect you have electronic ignition in which case you don't need to do this bit.

Once you have done this I would consider checking the exhaust manifold to see if there are any leaks.

Then check the carburetor set up. Check for leaks in seals that could possibly let more air into the carburetor. This is the end of the easy chaep stuff to do.

After this maybe check the jets in the carbs to see if they are blocked and the also the rest of the carb set up.

When did you last have a service? If it was sometime ago maybe consider more regular service intervals and that way you will keep on top of stuff like this.

Good luck, hope you manage to sort it.