Sneezing Yama 40Hp. on startup

[Weasel6]

My 94' Yamaha 40Hp manual start can be a booger to start. Got new plugs so thats not it. I'll pump up the bulb with the choke open, pull it a few times and it'll crank, run a second or two, "sneeze" and cut off. Repeat, except fuel prime, same. Repeat a time or two and then I'll give it some throttle to rev it up to warm up quicker. Once ot gets warm after a few minutes it'll purr like a kitten annd jump out the hole w/out hesitation. Let it sit for 30 min. and it'll sneeze and cut off just not as many times as initial start up. It's aggravating putting in at a busy landing and it won't stay running long enough to get out of the way until I "rev to warm". Are these motors as cold natured as a Merc.? Does something need to be adjusted? When its warm a half pull on the rope will crank her without even an "itchy nose". What her problem?

 

[jim dozier]

Re: Sneezing Yama 40Hp. on startup

I'm guessing that when you say you have the choke "open" you really mean the choke is "on" which in fact means its butterfly is closed. The description you give is an engine with the idle mixture set a tad too lean. Its OK when warm but a cold engine needs more fuel which is why we choke the air from them by closing the choke butterfly. Either the last person who set the idle mixture set it a tad too lean or gum has accumulated in the idle circuit a little and restricted the orifice and fuel flow so on a cold start it requires more choking and a longer warmup than it should. Try opening the idle mixture screws 1/8 turn. If that doesn't help it might require a carb rebuild. Also remove an airbox if there is one and inspect the choke butterflys to make sure they are completely "closed" tight when you actuate the choke. If they aren't tightly closed it makes cold starting hard.

 

[crzy4wlvs]

Re: Sneezing Yama 40Hp. on startup

I have the same probs with my motor also so im waiting to see what people say, good question!!

 

[Weasel6]

Re: Sneezing Yama 40Hp. on startup

You are correct on the choke aspect. I pull the choke lever out and then pump the bulb up. Is that ok or should I leave the lever in,pump bulb then pull lever and crank? Its not so much getting it to crank as it is getting it to stay running once it catches. It usually takes 3-4 pulls before it turns over cold but then it'll sneeze and cut off,2-3 pulls,catch,sneeze and cut off. About the 3rd or 4th series it stays long enough for me to rev up to precipitate warming. The throttle is at the "red" zone for starting. I think that ideally that normal is 3-4 pulls (cold),catch then idle then when throttle appliede it takes off without sneezing or hesitation.

 

[Backlash]

Re: Sneezing Yama 40Hp. on startup

Weasel16,<br />Jimd is right on the money. Back out the air/fuel mixture screw 1/4 turn (counterclockwise)and give it a try.<br />Backlash

 

[Weasel6]

Re: Sneezing Yama 40Hp. on startup

Which screw is it? My Seloc doesn't say which it is,only the idle speed / throttle stop screw. Also is there one on each carb. and each needs to be adjusted 1/8 to 1/4? Do it while idling or off.

 

[Weasel6]

Re: Sneezing Yama 40Hp. on startup

Anybody else want to comment or answer?