spark plug test - how much zap?

Hi, I'm going through a series of tests in the process of getting my vf500 running. I bought it as a non-runner and i've just swapped the spare engine that came with it, only problem is, it's not running either. I've only tested one of the spark plugs so far - pulled it out, earthed on the frame, turned the engine. It sparked, probably 2 - 3 times per second or so it seamed, and the spark looked a bit weak visually. Might this mean I have a weak spark and another problem that needs remedy. Any thoughts welcome, cheers

 

a really healthy spark looks bluish, not orange, but a low battery has some effect too.

test all 4.

generally, if u get any spark, you're good to go......

 

ok, that's good - the spark was blue and i charged the battery before the test. I'll do the others and get to work on the rest of the list.