Boss MGR350B in boat with a outboard motor. stereo works fine without motor running but you start it cuts in and out. with boat battery and even if you use another battery not connected to boat.

SOURCE: OUtboard motor tilt not working

There should be a hydraulic bypass valve screw on the tilt assembly. Usually a large slotted screw driver is needed to loosen the valve. The motor can now be lifted manually, but not with ease.

SOURCE: 40hp 1987 yamaha outboard motor will run for 30-60

Sound like the fuel pump is not keeping up with the engine's demand. Check it out. Good luck. Hope this helps.

SOURCE: Boat engine 1995 Johnson Outboard 70 HP

Ihave a 1991 70 hp Johnson outboard thats hard to start the first time but starts good after that. Seems to be flooded. Starting rpm seems to be low.

SOURCE: Free wiring diagram for 1978 Mercury Outboard 115 HP boat motor

I have a maintainance manual for this engine (I have the same one) with pages of wiring diagrams. What specific system/area are you interested in, I could scan in the page(s) and email them to you.

Mark

SOURCE: Yamaha 115hp 2 stroke Outboard Boat Motor. Went

is it carbureted or fuel injected? are your warning horns working? if it iscarbureted then a few easy test can be done to find out. if its fuel injected then its a little harder but not impossible.(1) check compression. without the year model I'm giving you a average numbers. all cylinders need to be over 100 lbs and equal each other within 5 lbs.(2) check spark. use a spark gap tester all cylinders should jump a half inch gap. if you have good compression and good spark fuel is the problem nine times out of ten. clean fuel lines replace primer bulb and replace all fuel filters. Yamaha has a gravity filter under the engine coul. take it to the lake if no improvement. clean carbs. same test to be and fuel system service used of fuel injected engines. if no improvement in engine preformance then you will have to take it to a dealer to test with computer.