1989 DT 55 stalls after an hour

[suzukidave]

Hi, I have a 2 cylinder commercial model manual start 1989 DT55. I believe it is similar to the Cabrea 50 and to the DT40 manual start.<br /><br />Anyway, the problem is that it will abruptly lose revs and die after a run of about an hour. This tends to happen as I back off the throttle while still on plane for a wake or to start in towards a dock. I normally run about 5200 rpm. 5500 rpm is manual rated WOT.<br /><br />Once it stalls like this it will not start unless I wait for a couple of hours. If I wait overnight it will run fine the next day and the problem may not repeat for a while. If I run it after a couple of hours wait it will only last about 45 minutes and then stall again (i.e., it will only get me most of the way home ;-( )<br /><br />I get strong blue spark on both cylinders when this happens but it won't fire for more than a second or two. Ether or pre-mix in the carbs makes no difference. It does not do this on short runs.<br /><br />I had this problem last year. Took it into the shop and had the fuel and electrical system checked. The mechanic said electrical was fine and fuel pump was fine and cleaned all the fuel lines. Nothing askew except a missing o-ring in the fuel filter. I had the carbs rebuilt because they were dirty although we both doubted this was the problem. It pees real good and I put in a new impellor last year. <br /><br />Now it is doing it again. My favourtie lunch spot is one hour away by boat. This is bugging me. Except for the spark I would suspect powerpack overheating. Does anyone have a suggestion?