90 Hp strange problem

I have a 2004 - 90 hp Johnson. For three years it ran perfect. Last year, I started having this problem. I run the boat for a few hours at 3500 -4000 rpm's, it runs perfect. Suddenly the engine stops. It will restart, but only for a short few seconds. I was towed to port. The next day I came down to accept a tow to a repair marina, when the boat started and ran perfect for perhaps 45 minutes. I left the boat with the repair shop, but they found no problem. This was an authorized Johnson dealer. I had the boat pulled and took it to the dealer that sold me the engine. They too tested it and found no problem. May-2008 put the boat into it's slip, ran it 3 times, no problem.
Then it happened again, after a 1 hour run at 3500-4000 rpms the engine quite. Towed back to port. Next dat, I started it and it ran fine.
None of the service mechanics, can find the problem, short of starting every part in the engine, one at a time. Does anyone have an answere. Jim

Re: 90 Hp strange problem

It only happens when the engine is hot and has been hot for a while.

I would suspect a heat related ignition failure. These can be tracked down with a hair dryer.

Re: 90 Hp strange problem

If this is a 60 degree engine, check the pack output to the ignition coils, cold engine cranking rpms, then check same engine hot idle, or just replace the power pack and ignition coils. Do the techs own a peak reading meter?