Yamaha 40 dying revs/coughing

[dazza_red]

I have a yamaha 40VETO 2 stroke (approx 2000 model) 200 hrs, full service history. This week, motor seemed to be missing occasionally with cough. Full throttle only managed 4500 revs, usually 5500. Maintaining FULL THROTTLE, revs slowly reduced to 3000 and losing power. At 3000 it coughed a few times, fluctuated up & down between 3000-4000 revs. Then after 10 minutes of this, it kicked in back up to 5500 normal full revs! Any ideas why? This is the 2nd trip this has happened. Could this be the CDI unit (electrical).
Previous day, motor would stop when in neutral position, and when restart would run 2-3 seconds then snuff out numerous times. Fuel and spark checked and no issues.

Any thoughts/suggestions?? Thanks in advance

[pstephens46]

Fuel issues are by far the most common problem on this forum. A cdi actually crapping out is pretty rare. Low hours on a 2000 model. Lots of sitting makes it a prime candidate for carb issues. Play the odds and start there. Most likely will need to be cleaned throughly.

[dazza_red]

yeah has done little work and does sit for long periods of time. Thanks for the advice i'll start playing.

[TownsendsFJR1300]

Your motor doesn't show on the US parts website, I gather you not in the US?

Is this a carbed engine or Fuel injected?

If carbed, plus 1 ^^ on your carbs being clogged/ varnished up. Especially if stored with un-stabilized fuel.

I see the carbs coming off and getting cleaned... Removing the main and idle jets and LOOKING thru them is mandatory.

If the fuel is old in the tank, dump it...


.

[99yam40]

this cough you speak about sounds like a lean sneeze.
this can damage the fuel pump if it happens on #3, so check it also when cleaning the carbs.

and make sure to flush the lines, you do not want any bad stuff from them to hit the cleaned carbs when fired back up.