Backfire

[Escambia]

2001 Yamaha 115 2 stroke, backfires once right before motor cranks. Happens most time if not been run for a week or so. Motor is not stored trimmed up or down but in the middle when it barley touches the trim sticks(not sure what the official term is). Is this normal? Do I need to adjust the motor while it's not in use? Confused!!!

 

[Sea Rider]

Is the timing advance well synched with carbs ? For that will need to figure it out or check the Service Manual tech specs on how to check it or synch it right if happen to be bit off from what needs to be.

Happy Boating

 

[99yam40]

back fire means different things to different people.
use to it was when the motor would fire back up thru the carb.
some call a loud pop out the exhaust a backfire

what exactly is your definition of Backfire?

 

[Escambia]

Well I guess I'd call it a pop out of the exhaust. Nuthin loud or crazy just a pop.

 

[99yam40]

is the lower unit and exhaust down in the water?
maybe that is why it is a small pop, muffled by the water.

if on the exhaust that means that an explosive mixture of fuel and air is being lit off in the exhaust.
maybe extra fuel is going thru the cylinders at 1st where the spark plugs cannot light it off inside the cylinders and finally gets enough air in the exhaust to become ignitable.

if it is inside the crankcase itself, it could be what is called a lean sneeze and that could damage seals and diaphrams

 

[Escambia]

Running on muffs with water hose, should have mentioned that. Doesn't do it all the time just when sits up for a little while

 

[robert graham]

The next time you let the motor down to start it, try pumping the primer bulb a few times to be sure carb float chambers are full....then start the motor...

 

[99yam40]

Running on muffs with water hose, should have mentioned that. Doesn't do it all the time just when sits up for a little while

I kind of doubt that it is popping out the exhaust if it is not loud.
probably a lean sneeze from being too lean

 

[Escambia]

I preciate it fellers, maybe it's just me worrin about things I shouldnt be worried about. We gonna take her out this Saturday and try it.

 

[Sea Rider]

Had same issue with a Yam 140 HP while being flushed with muffs, one of the 4 carbs was found way out of idle adjustment, adjusting carb correctly solved the noisy issue. Check that engine is using correct plug number and well gapped to specs.

Happy Boating

 

[99yam40]

I preciate it fellers, maybe it's just me worrin about things I shouldnt be worried about. We gonna take her out this Saturday and try it.

lean sneeze is something to worry about.
it can damage crankcase seals and fuel pump diaphragms

 

[Escambia]

Well dam I rekon that is something to be worry about. Carburators may need a little twerkin?