1997 70hp Yamaha 2-stroke throttle adjust question

[waitsfan]

We recently started having problems with our 70hp outboard engine. It started fine in the morning, ran great for 30 minutes (cruising time to our first site), and then wouldn't start up again after sitting for an hour or so. I checked all the plugs, the fuel filter, and the battery connections. After messing around with it for a while, it started ok, but didn't have much power. It would run okay for 5 minutes or so and then would lose power and die. It would start right up and run okay for another 5 minutes....and so on.
We paid a guy at the dock to clean the carbs. He also adjusted the idle speed. Yesterday it started up fine, idled a bit too high, but otherwise sounded fine. The problem was that there was a huge loss in power. WOT felt like about 1/4 throttle. It started fine and ran ok (albeit very underpowered) until the ride home, when it died and went back to the problems we had before the carbs were cleaned.
I am hoping that a simple adjustment to the throttle will solve the problem, but I am obviously not very experienced with this type of problem. Any advice would be welcome! Thanks.

 

[99yam40]

Re: 1997 70hp Yamaha 2-stroke throttle adjust question

You need to check the condition of your motor now that you have run it for a while with a problem and may have been running lean and hurt a piston.

Check compression on all cylinders, check spark on all cylinders with a spark tester, check what the timing is doing at idle and WOT. Make sure you fuel is fresh and not contaminated with water or other trash.
If all that is still good then look at the fuel system .http://forums.iboats.com/showthread.php?t=283363
Check fuel supply pressure and vacuum and check for air leaks. This will tell if there is a restriction and that the pump is functioning properly. If all is well then clean tha carbs real good and adjust properly like your manual states.
If you do not have a manual then get a Yamaha factory service manual for your motor, it will save you money and time if you plan on working on it yourself.

 

[waitsfan]

Re: 1997 70hp Yamaha 2-stroke throttle adjust question

Thanks for the advice! I just got back from checking on the throttle adjustment. I adjusted the idle while I was there and decided that I need to check the fuel pump. The link you included looks incredible! I will do exactly that.