I reciently rebuilt a 1985 yamaha 70hp outboard
idles and starts great,when using muffs in yard
motor starts and idles great in water under load,as soon as you put it into gear it kills,also with motor running you pull the spark plug wire off of the #1 or top plug it kills, but does not kill when you do the same to the other 2 pulgs motor contue to run
(all carbs have been rebuilt)
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Hi, your problem is simple you either have a head gasket gone or a exhaust plate/gasket gone. Either will let water into a cylinder which is why it ran ok without water. You should also check the water pump in the leg as you have now run it without water. Regards Phil.
Hi. If you just want to run the motor then you can do it in you driveway. Go to a sports store with boating equipment and ask for "Muffs" to run your boat motor out of water. You can see a pictures of outboard motor muffs on google images:
Take the muffs and place them over the water intakes located above the propeller (look like vents on each side). Hook a garden hose up the muffs and start water flow. Make sure nothing is near the propeller. Make sure to pump the bulb in the fuel line to the motor until it stiffens. Crank the motor. When the motor starts, you should see water start to flow out of the back of the motor near the cover and out of the center of the propeller with the exhaust. You must keep water flow to the motor using the muffs while it is running or it will burn up.
not enough information on the motor. what year and model? but all yamaha outboards are shut down by the C.D.I. being grounded by the key switch or the emergency kill switch. the cheapest thing to test or replace is the key switch and the emergency kill. with more info on engine I can help you further.
I have found that 99 percent of the time when this happens it is carb related. It is very possible that you picked a a small piece of grit or trash in the high speed jet of one, or both, of your carbs. I would be willing to bet that pulling the carbs and cleaning them will resolve your problem. I am almost positive that will fix your problem, mainly because it sounds like you've already tried everything else. I had this same problem last season, and what had happened was I left the vent open on my fuel tank, we got a shower, and I pulled just a small bit of water into the carb and that was it, she would not do anything over idle until I pulled the carbs and cleaned them. i even put the water muffs on it and let it run in the yard for about an hour thinking that it would burn the water out, but i was wrong. Anyway, clean the carbs and i think you'll be in good shape, Good Luck.
First, always have the motor in water or with a hose and muffs when you run it. It is simple to fix if all the parts are there. Let me put it this way. If you know where the air mixture adjustment is on the carburetor you turn this screw until the engine speeds up at idle to a maximum rpm, then back in 1/4 turn. Adjust throttle stop screws to achieve a minimum base idle. If this seems complicated, take it to an outboard place or lawnmower shop(if you have a hose and muffs). Its a 15 minute job and will last until its changed.
I had the exact same problem. The problem was that there was a piece of dirt in main jet of the bottom carb. The engine would rev up aton fast idle but would not produce enough power to plane the boat due to the lack of fuel flowing through the carb. Cleaned all three carbs. Motor ran like a champ.