trouble with my yamaha 40 hp engine 2003 model

i have been having some trouble with my yahmaha engine whenever i try to start it up it gives a hard start and when it does start it coughs and shuts down. Whenever am running it at high speed it runs fine certain times them all of a sudden it just slows down and picks up again i tried new plugs in it thinking the old ones were not firing but the problem still exists so i was wondering if it could be a fuel problem or somthing. Lastly whenever it does idle without coughing and shuting down for a few minutes whenever i put it in gear the engine starts jurkin up and makes a clogged up sound as tho its been clogged by oil or somthing.any help would be much apricated thx

[boats.net]

Probably needs carbs cleaned.

i have been having some trouble with my yahmaha engine whenever i try to start it up it gives a hard start and when it does start it coughs and shuts down. Whenever am running it at high speed it runs fine certain times them all of a sudden it just slows down and picks up again i tried new plugs in it thinking the old ones were not firing but the problem still exists so i was wondering if it could be a fuel problem or somthing. Lastly whenever it does idle without coughing and shuting down for a few minutes whenever i put it in gear the engine starts jurkin up and makes a clogged up sound as tho its been clogged by oil or somthing.any help would be much apricated thx

dude, I have a 50 hp 4 stroke (yr 2000) that is doing the SAME thing - new thermostat, new plugs, fresh gas, gas supply re-do, compression check - carbs re-synced - runs great sometimes - other times like a tractor - this a common thing with these Yamahas? My evinrudes never had a problem AND were easier to work on ..... my next motor prob won't be a Yamaha...

Did you resolve Issue?

i have been having some trouble with my yahmaha engine whenever i try to start it up it gives a hard start and when it does start it coughs and shuts down. Whenever am running it at high speed it runs fine certain times them all of a sudden it just slows down and picks up again i tried new plugs in it thinking the old ones were not firing but the problem still exists so i was wondering if it could be a fuel problem or somthing. Lastly whenever it does idle without coughing and shuting down for a few minutes whenever i put it in gear the engine starts jurkin up and makes a clogged up sound as tho its been clogged by oil or somthing.any help would be much apricated thx

Did you resolve this issue? I have a 40hp two stroke that runs fine at high speed, but runs rought at idle and then kills. Just trying to see what my issue is. Sounds similar to yours.

[bigfish1229]

carbs need cleaned on both engines

[tmcdade]

don't know if this is applicable to your motors, had similar problem with my 2000 F25, found problem in the mechanical fuel pump, the plunger was sticking, and sometimes would stay retracted (stuck up inside the pump, so it did not get stroke from cam) hope this helps.
Regards Tom