ch312 Posted April 22, 2011 Report Share Posted April 22, 2011 my yamaha 15hp 2 stroke outboard idles very rough and will "cough" at idle and sometimes die because of this. it runs totally fine from idle to full throttle when the choke is at half. the fuel filter is spotless and i'm using new gas. i don't know squat about these thing's. where should i start? does anyone know the factory settings (# of turns out) for the mixture and idle screws so i can check those first? Link to comment Share on other sites More sharing options...
irishfield Posted April 22, 2011 Report Share Posted April 22, 2011 Running better with 1/2 choke says it needs to be a tad richer (choke = less air) to run than the jets are letting it with no choke. So try the idle screw ccw a 1/4 turn. Generally on most any carb they are set 1.25 to 1.5 turns out from closed... ie turn cw to lightly seat closed.. then ccw 1.5 turns to start and tinker each way leaner/richer from there in small increments. Start off by seeing where yours is to start. Count the turns cw until it seats and you at least have a "return" point if that doesn't clean up the problem. The next crowd is gonna be.. pour the seafoam to it... Link to comment Share on other sites More sharing options...
Old Man Posted April 22, 2011 Report Share Posted April 22, 2011 If adjusting the idle screwdoes't make a difference , it may be a plugged pilot jet. You may need to remove the carb, take it apart, and give it a good cleaning by soaking in carb cleaner. Before reassembling, run some fine wire or heavy mono fishing line through the pilot jet to make sure it's clear. Link to comment Share on other sites More sharing options...
Fisherman Posted April 22, 2011 Report Share Posted April 22, 2011 A healthy dose of SEAFOAM in the gas tank, not through the carb intake, it will slowly clean out all the tiny passages and jets in the carb. That's why I drain my carbs on summer equipment to store over the winter, no funky gas to dry and gum things up. If it's that bad you may have to take the carb apart and clean it with a product like Revive, should be able to get it at Car Quest/NAPA. I did an old 4 stroke carb with it and the gum deposits washed out after 20 minutes, ran like new after that. Link to comment Share on other sites More sharing options...
ch312 Posted April 23, 2011 Author Report Share Posted April 23, 2011 so i set the mixture at 1.5 turns out and it still only runs properly at half choke. i went each way about 3/4 of a turn and it made no difference. there's some oil on the plugs that i installed last year so i cleaned those up, but it made no difference. looks like i get to clean the carb today Link to comment Share on other sites More sharing options...
brifishrgy Posted April 23, 2011 Report Share Posted April 23, 2011 do you have to prime the ball on the gas line after it stalls? , if you have to prime it check the vent on the tank Link to comment Share on other sites More sharing options...
pikehunter Posted April 23, 2011 Report Share Posted April 23, 2011 How old is the gas? If it's leftover from last season then there's the problem. Even with conditioner/stabilizer in it I don't use it in the outboard if it's that old. Check your sparkplugs too. I had a rough running incident once, had to turn up the idle and keep the throttle turned up a bit. Went and got a fresh tank of gas and it ran great! Link to comment Share on other sites More sharing options...
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