Engine runs fine at high speed slow down it stops .can start it again at open throttle but dies again as soon as you back the throttle off to engage the gear
Start off by cleaning carbs,sounds like idle jets are blocked
SOURCE: motor died when I slowed down, and wouldn't crank again
Some motors have limit switches built in to kill the ignition if the motor is started at odd angles. The trim is different for speed and passenger load. The limit switches may be adjustable to eliminate that problem. Usually when you go to dock the boat will fish tail if the trim is too extreme for slow speeds.
SOURCE: Chrysler 70 HP outboard motor dies when pushing throttle
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.
SOURCE: 2003 115 mercury efi losing power
I am a Mercury certified technician. What you need to do is take it to a Mercury dealer and have them hook it up to the computer. It sounds like the engine could be in Guardian mode or possibly a high RPM misfire. It is not something that is common and the computer program that Mercury has for those is able to test misfires and all sorts of cool stuff. It can also tell you if the engine was broke in properly, how many actual running hours are on it and even at what RPM each hour was ran. It will be able to bring up all faults that it has had in the past and any faults that are current. I know that you are probably looking for a quick, easy fix but for this problem I dont think that there is any way around taking the engine in. For what it is worth, if they charge you for more than 2 hours to run it on the computer then take it somewhere else. I can fully test the engine with the computer in about an hour. The only reason that it would take any longer is if they had to put it in the water to duplicate the problem but most shops will have a test tank that is capable of running your engine under a load at full throttle. Sorry for the bad news but I cant think of any other way and throwing new parts at it is just going to get expensive quick.
SOURCE: When I start my 10hp mercury outboard after
Be sure to run the recommended fuel mix. most modern 2 stroke outboard engines run on 100 to 1, some times the mix is on a decal inside the cowl.
Cheers, Timo.
Here are the most common causes of idle surge, stalls at stops, slow idle speed, erratic idle speed, rough idle and engine hesitation (and other problems), it is in most cases the idle speed control air-bypass valve and or throttle valve and upper intake, these area's get full of gunk and combustion residue over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake
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