I have a 1983 inboard- outboard 3.8 litre o.m.c. 6 cylender boat engine. the boat startsoff and runs well. After you push throttle above 2000 rpm's the motor revs, but the motor ceases to push or move the boat forward.
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Very sorry I don't know anything about a Viper Sport. Is this a gas motor ( 4 cylinder or more ) or is it a electric motor. Is it inboard or outboard. Is there a brand name on the motor ? ( technically a motor is electrical and an engine is powered by fuel ) Without this info the limited number of people that can help are dealers or other owners of this type of boat. Again sorry, EEL Canada
BOAT#1: I experienced the same thing when I had a mouse nest in my water box. When ever you turned left the nest would plug the exhaust and cause an RPM drop till the boat slowed down. BOAT#2: Another thing that can cause intermittent running is moisture in the electronics box. If the box has water in it, open it up overnight to let it dry out, then reseal it and it should run normally again. BOAT#3: The third thing that has caused the same issue you described, was dirty carburetors (SS XI) from bad gas and improper storage. This was made worse because there were also bad spark plug caps on the machine. Hope one of these solutions fixes your problem.
The carberator is gravity fed and there is propbably gunk in it, when you give it more throttle, it needs more gas but can't get it. Then a build up of gas in the float bowl occurs and nothing works right. It has happened to me and its aggravating, do a complete rebuild on the carb or just replace it and you will be happier quicker.
it sounds like your lower unit pump is going out
hook it to a fresh water hose and run the engine and see if more water comes out of the exaust if it is more then i would replace the lower unit pump check and see if the screens on the lower unit are plug up with seaweed and clean them that would restric the flow of water
Twin outboards should be mounted at the same level. One should be standard rotation and one should be counterrotation. The propellers should be the same pitch and size but opposite rotation.
Just check which hole on the motor mount that the top mounting bolt goes through. Should be the same one on both motors.
You may want to call the manufacture of the boat and see it there was something unique about that boat that required mounting them that way. You will need the serial number from the hull of your boat when you call.
Fuel system has to hold 3 to 7 psi for ten minutes. fix any leaks. Check to make sure that your water temp sender is working right and or that the water system is not clogged.
If it thinkd that it is over heating the rev limiter will drop to a lower rpm. hope that helps
Not familiar with that specific motor but had similar vintage smaller HP Johnsons. From my experience it sounds like it could be that the high speed carb adjustment is too lean. What I would try is running the backing off the high speed screw 1/4 turn to 3/4 turn, then test. If works better, screw back in in 1/8 turn increments until the problem recurs, then back out 1/4 turn and leave it there.
With the newer yamaha jet boats your route of easiest resistance is gonna be to take the boat to a Yam dealer so they can put a diagnostic machine on it. Alot of sensor problems can be solved much easier and cheaper after running the diagnostic and pinpointing exactly what the issue is. The lights on the dash are for high temp and low oil. If you checked the water temp and it seemed ok, check your oil levels.
the inside of the prop has a rubber between the prop itself and the inside splines to act as a shock absorber,say if you were to hit a rock. that rubber had spun out and the splines are turning inside the prop. the prop is screwed. seen it 100 times before.