1999 Merc 135, 2 stoke, carburetors, stalling under load

[skime219]

Engine cranks fine, idle good, can run the RPMs up no problem in neutral.
In gear will idle and run at low speed of 1,000 to 1,200 RPMs.
When attempting to accelerating engine sputters and dies, cranks right back up.
All suggestions appreciated.
dw

[skime219]

Update after a full day of effort.
The motor has 360 hours on it, located in central Alabama--no harsh winters--, seasonal maintenance, stored under shed and covered year round.
Replaced all fuel lines and no ethanol in fuel for over 3 years since that work, premium gas and Merc oil since new.
Today:
Changed the spark plugs, new fuel filter and added a water separator filter. Pulled the prop and checked all parts, cleaned, grease and reassembled.
Same behavior, no power under load, cranks fine, easy to rev up to 3,000 or so RPM with no problem.

Seems I had an issue several years back with a power pack....any knowledge on that would be helpful.
How do you test and is it an easy DIY replace?
Any other items to check??


Thanks to all for any help.
dw

[boats.net]

Could be misfiring on one or more cylinders, have you checked to see if getting a good spark on all cylinders? With a peak reading voltmeter you can check the peak voltage output of trigger coils, stator and switch box output. If spark is good then may need to remove and clean carbs.

[skime219]

Had to call in reinforcements, left bank of engine not firing at all, bad power pack, also replacing stator per recommendation from Mercury.
All part in and work to be done Friday 8/7/20.
Thanks much for the help!
JDW

[boats.net]

Glad you found problem, that is a common problem with Mercury ignition systems.