Little background...took the boat out the other day, max rpms was only about 3800...took 'er home and went thru it, found a coil that had burnt back the copper where the wire plugs into...replaced that, took it back out onto the water, 5000 rpm no problem, ended that day by decarbing the motor...previous owner said he had never done that...Well, took her out today, she was running like a champ, by the end of the day, the hole shot was suffering and I lost 500 rpms. you can always tell when its going to act up because it is hard to start after shutting it down to load a skier......and when you nail the throttle, you get about half way and it just dies, if you pull back on the throttle and kinda ease into it...it goes. One thing I did do was change from Shell Nautilus oil to Quicksilver plus.Any ideas, hints or suggestions?
some on this board have said that after a decarb "change the plugs" as for thr oil a lot of us use super tech tcw3 from wall mart. use the search and put in tcw3 for more info on oil.Richard
did a compression test after I changed the coil, the old girl had 120 psi straight across...yup, I changed the plugs after the decarb.......second trip out I pulled the plugs and there was a fair amount of carbon balled up on a few....but I hear thats normal after a decarb, may have to clean plugs a few times until all the carbon is thrown..I went to wallmart here in Calgary, But I couldnt find that oil, but how can you go wrong with Quicksilver?
There is nothing wrong with mercury oil. I would have to guess there is a fuel delivery problem, because you say the problem exists on startup and higher rpms. However, you can't rule out ignition at this point. I would try to rule out fuel delivery problems (you can definately rule out head gasket since there isn't one.) When the motor bogs get someone to pump the fuel bulb to see if that changes anything. Or after it bogs and dies, pull the plugs to see if all are wet with gas.When the motor is acting up, is the idle quality affected?
What200..The engine idles great since I changed the coil, before it used to stall when put in gear...Its definitely a wierd one 'cause its intermittant, sometimes you can put the throttle full open and the thing jumps and planes right away, next time, she'll sputter, and unless you back out of it, it will die....I'm an auto mechanic by trade, and I'm **** sure the thing is leaning out....I'm tending to think that maybe the fuel pump diaghram should be changed out....probably a good place to start.Another thing is, why is it hard to start when its hot?? These **** outboards are going to be the death of me!!lolJames
If you pump the bulb while it is bogging that helps I think that would point to either the diapham or a vacuum leak.Inlines are supposed to be hard to start cold not hot. I think that would point towards your fuel pump losing prime somewhere.The only thing about it, is that if the problem turns on and off like a switch that would be more like a stator or switchbox problem, but could be diagnosed with a timing light on each plug wire.
What200......If it was a stator or switchbox, I think it would lose more than 500 rpm.....when the coil was shot, the best it would do was about 3800 rpm...I think its a fuel problem.Thnx for the suggestionsJames
I have a 79 140hp Mariner L6 that has had very similar symptoms. I had a new fuel line/bulb I installed and did not change out the receiver in the motor that the fuel line connects to. There was enough difference to restrict the flow and caused similar problems as you had. Just a thought, good luck.
82 mariner 90 hp running weird
Well, took her out today, she was running like a champ, by the end of the day, the hole shot was suffering and I lost 500 rpms. 
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