Need help motor won’t start and keeps backfiring

Smutty

Cadet
Joined
May 15, 2020
Messages
13
I have a 2006 25 hp 2 stroke 2 cylinder manual start outboard Yamaha #25MSH I got the motor from my sisters house and have no idea how long it’s been sitting out I was only able to get it started about 3 time but really hard to start take bout probably 30 or 40 pulls repeatedly before it started than when I’d lower the idle down it would die out almost immediately. I’ve had the carbs cleaned replaced both the air mixture screws/pilot screws on the carbs the fuel filter was leaking so I replaced the o ring and stopped that problems replaced both spark plugs and set the proper gap for them also replaced one of the coil packs got brand new fuel tank and hose with 100-1 gas and oil mix I seem to be holding fuel all the way to the carbs I opened the drain plug on top carb fuel came out but I wasn’t able to get to the bottom carb to check it one of the carbs seem to be seaping fuel tho but not a lot at all like a tiny drop rarely but something seems to me leaking just a little bit so I got repair kit for the carbs so I can replace the seals both my cylinders are holding compression at about 105-110 the only thing is one of my spark plugs looks like it has oil or something on it while the other still looks brand new and another thing I checked was the kill switch someone must’ve lost the clip to it cause they got 2 little zip ties between it to keep it from closing over all it’s a really clean motor i opened the drain plug on the bottom of the motor and had clean oil come out now the problem is I can’t get it start anymore and it keeps backfiring like popping when I try to start it like maybe once every 6 pulls or so I tried swapping the wires around on the plugs and still did it not sure where to go from here I also tried resetting the mixture screws and the idle screw still pops the cdi has a few wires not hooked up but don’t reallt see anywhere they could go plus I figured if it started before than wiring shouldn’t be the issue but I don’t know what to do now.
 

Zook4184

Seaman Apprentice
Joined
Apr 29, 2020
Messages
43
I’m working on a 2 cylinder outboard that’s doing the same thing if you have good spark and fuel in both cylinders and one spark plug is black and the other looks normal And if it has 2 carbs check that cylinder that has the black spark plug and check to see if it is dead by pulling the spark plug wire while it is running if it keeps running that cylinder that carb that matches that cylinder is most likely flooding that cylinder and not allowing it to fire cleancarbs again once you get both cylinders fire the piping and running rough should get smother just my experience hope it helps
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,092
Smutty----Check the flywheel key.------A clean sparkplug may also indicate no spark.
 

Smutty

Cadet
Joined
May 15, 2020
Messages
13
I did some more inspecting on the motor and pulled some things apart the flywheel key is sheared and broken in half I got some new ones coming but I also realized the timing base is stiff or stuck when I screw it to the retainer I took it cleaned reall good inspected it I sprayed just a little bit of wd-40 in it to try and get it to slide but that’s not the problem it’ll move perfect and everything if I screw it in just enough to hold the retainer and base together it’ll move perfect but when ever I start snuggin them up its as f*** to move any suggestions on that??
 
Top