random drop in power

[wombat10]

G'day all
I have a 1981 90hp johnson (j90tlcim) that drops rev's about 50% at random intervals for varying lengths of time, i can go all day without it happening or it can happen dozens of times a trip, it can last from 2 seconds to 30 or 40 seconds the run normal, it happens anywhere in the rev range from idle to wot.
as it seems to lose 50% regardless of the revs i am leaning towards a failing powerpack or maybe a bad wire to one of them, but the randomness of the problem is confusing me (not a hard thing to do)

spark is strong and loud on each lead when tested, compression on all cylinders is within 10%, new fuel pump, rectifier, plugs and leads.

any ideas appreciated.

 

[racerone]

Check the pins in the connecters for the powerpacks ( should be the same depth on all ) --------------Hook up a timing light when you are running to help pinpoint which cylinders are loosing spark.

 

[wombat10]

thanks racer, i'll check the pins tomorrow. i have had a timing light on each cylinder but haven't been able to "catch it in the act" yet.
i did however catch a cracked coil by seeing a small spark where there shouldnt be one while running at night with the cowl off and timing light laying on the floor.

 

[Boobie]

Have you looked into the timing lite to see if you have any black spots when the prob occurs??