40 HP (40TRLU) 2 stroke power/RPM Loss

[Boating Newbee]

Anyone have and idea why a 1996 40TRLU 2 stoke would lose power after 1-3 min running high RPM on the water. Seems to take off great, but after 1-3 min of running high speed, the RPM/speed slows to @ 3000 rpm and doesn't go any faster 5-7mph. Took off air cleaner and watched fuel entering carbs and it doesn't fluctate. It's almost as if a cyclinder is down, but if I pull a plug wire you can tell difference. It almost feels like cavitation, but the boat planes out great when it starts off and runs great for a minute, then begins to just slows down. Changed plugs, no help.

 

[99yam40]

Re: 40 HP (40TRLU) 2 stroke power/RPM Loss

inductive timing light hooked to the individual plug wires should show if it is loosing spark to one of the plugs.

While hooked to #1 see that timing is in spec while problem is there

Check to see if fuel pump is leaking fuel into crankcase through pulse port

 

[Boating Newbee]

Re: 40 HP (40TRLU) 2 stroke power/RPM Loss

ok thank. I'll have to see if I can borrow timer. Doesn' happen on land, only on the water, and once it's slowed to 3,000 + - , If I shift to reverse then forward again, takes off like a champ for 1-3 min again. Friend thought fuel issue too as if bowl empties, and doesn't fill fast enough and then boggs out, but flow out of jets lookked fine. I don't see any fuel stains on the water though, but I'll keep tryig. Thanks