need help on cbr600

I am helping ny nephew with his first bike. He bought one that has set for years in a barn. I tore the carbs down and freed the linkage and degunked the bowls and jets. This thing fired right up and ran great a couple days, now it acts like no spark on 3 plugs. The pulse generator is working and the coils both test good. The plugs are new at time of purchase, we installed them at my house. I feel the plugs may be the problem, but wondered if anyone had a similar instance that Iam overlooking. I am open to all suggestions.

pull the plugs back out and check them. they may be fouled from rust or old fuel. thats where i would start. sounds like a cool project.. Good luck.. Griz
ps also check the plug wires they may be old and cracked. and shorting out.

I put old plugs from my bike on the end of the wires and grounded the bases with jumpercables, the plugs all sparked. this confirms in my mind the plugs are his problem now.