late 80'S yamaha 70 hp help needed plz

[stageboy007]

will start and idle fine, but upon throddle up, it misses.... di duh,duh,duh,duh. the motor jerks slightly every time it misses. I just bought the boat and am new to the big motors. where should I start? plugs? also the power trim works i was told, but leaks the oil. is that just a seal replacement? the motor still whirrs when i push the button so it is still getting power. thx guys

 

[BruceAML]

Re: late 80'S yamaha 70 hp help needed plz

It would be best if you posted the exact model of your 70 hp. Did you clean the fuel filter? Are the correct spark plugs installed and gapped correctly? Are the 3 carburetors clean? Is the engine getting fuel? Is there oil in the oil tank and is it pumping to all 3 cylinders? Are the coils working properly?

 

[drewmitch44]

Re: late 80'S yamaha 70 hp help needed plz

Mine does that every once in a whyle at idle. Its smooth and then its like i just hit a log or somethig. it will do that when running on the muffs too so i know its not a log unless there is a log that pops up out of the ground. I never posted cause im not as creative as you are with typing the sounds.lol Thats cool. how did you say that "di duh duh duh". mine goes more like di di di di di di duh di di di di di di duh. And my tilt and trim whirrs too. Man thats good stuff. But seriously though i always thought it was a timing thing with mine. It only happens every now and then so ill let it be. I hope its not something else like not getting enough oil and its scoring the cylinder wall every time.

 

[warrend]

Re: late 80'S yamaha 70 hp help needed plz

I have the exact same problem with my 85. Did you find what the problem was ?

 

[sc_shane]

Re: late 80'S yamaha 70 hp help needed plz

Has the boat been sitting for months before you bought it? I had a similar problem with mine after it sat for 9 months, but it wouldn't idle without the high idle throttle pulled up either. I've got an '89 90HP which should be about the same engine you have (I'm no professional mechanic by any means). I had the carbs rebuilt by a top knotch mechanic and she ran great ever since. It should also be noted, I changed the plugs (properly gapped, of course) to the called for NGKs and also replaced the fuel filter before taking it to a mechanic. (ran me $350 for the whole bill). If I were you, I'd douse the carbs in Sea Foam, clean them up real good a couple of times, replace the spark plugs and see what happens. That's about $12 and an hour or two of your time - well worth the effort regardless if it fixes your problem or not.